Valve Types: A Guide To Choosing The Right Valve
Table of Contents
- What is a valve?
- Characteristics of valves
- Classification of valves
- Size of the valve
- What is the pressure rating of the valve?
- What is the classification of valve standards?
- What are the types of valve sealing surfaces?
- The preparation method of the valve model
- Selection of valve materials
- Valve pressure test method
- The basic content of valve design
- How are valves made?
- Uses of valves
- How to choose the right valve?
- Select the valve according to the flow characteristics
- Select the valve according to the connection form
- Select the valve according to the medium performance
- Select valves according to temperature and pressure
- Determine the diameter of the valve according to the flow rate and flow rate
- Comprehensively determine the structure type of the valve according to the working conditions and process operation
- Selection of driving valve
- Automatic valve selection
- How to purchase valves?
- The characteristics of the valve are use characteristics and structural characteristics.
- The steps to purchase valves.
- Valve standards and specifications that should be understood
- The basis for purchasing valves
- Marking and identification of valves
- Identification of valve painting
- Identification of valves materials
- Identification of valves
- Ordering of valves
In fluid piping system, valve is the control element, and its investment accounts for about 30%-50% of the piping project cost. The main functions of valves are opening and closing, throttling, regulating flow, isolating equipment and pipeline systems, preventing backflow of media, regulating and draining pressure, etc. Valve is also the most complex components in the pipeline, it is generally assembled from multiple parts, high technical content. With the rapid development of the petrochemical industry, petrochemical production equipment in the media mostly toxic, flammable, explosive and corrosive characteristics, operating conditions are more complex and harsh, operating temperature and pressure is high, the start-up cycle is long, once the valve failure, the light leads to media leakage, both pollution of the environment and economic losses, the heavy lead to device shutdown, and even cause malignant accidents. Therefore, in the design of the piping system, the scientific and reasonable selection of valves can reduce the construction costs of the device, but also to ensure the safe operation of production. The article mainly introduces a variety of commonly used valves such as gate valves, globe valves, throttle valves, plug valves, ball valves, diaphragm adjustment valves and other selection methods.
Valves are mechanical devices that control the flow and pressure of fluids in a hydraulic or air system. They are essential components of piping systems that convey liquids, gases, steam, sludge, etc.
There are many different types of valves to choose from, each with different characteristics, capacities and uses. There are different methods of operation available: manual, pneumatic, electric, etc.
Characteristics of valves
There are two general characteristics of valves, use characteristics and structural characteristics.
Use characteristics: it determines the main performance and use of the valve, belonging to the valve use characteristics are: the type of valve (closed-circuit valves, regulating valves, safety valves, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.); valve main parts (valve body, bonnet, stem, valve flap, sealing surface) materials; valve transmission mode, etc..
Structural characteristics: it determines the valve installation, repair, maintenance and other methods of some structural characteristics, belonging to the structural characteristics are: the structure of the valve length and overall height, the form of connection with the pipeline (flange connection, threaded connection, clamp connection, external thread connection, welded end connection, etc.); the form of sealing surface (inlay ring, threaded ring, weld, spray welding, valve body); stem structure form (rotary rod, lift (lever), etc.
Classification of valves
What types of valves are there? There are many types of valves, complex varieties, mainly gate valves, globe valves, throttle valves, butterfly valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, steam traps and emergency shut-off valves, etc., which are commonly used gate valves, globe valves, throttle valves, plug valves, butterfly valves, ball valves, check valves, diaphragm valves.
First, the valve can be divided into two main categories.
The first type of automatic valve: rely on the medium (liquid, gas) itself and the ability to act on its own valve.
Such as check valves, safety valves, control valves, traps, pressure reducing valves, etc.
The second type of drive valve: with the help of manual, electric, hydraulic, pneumatic to manipulate the action of the valve.
Such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc.
Second, according to the structural characteristics, according to the direction of movement of the closing member relative to the valve seat can be divided into.
- 1. Gate: the closing member moves along the center of the valve seat.
- 2. Gate shape: the closing member moves along the center of the vertical valve seat.
- 3. Plug and ball: the closing member is a plunger or ball, rotating around its own centerline.
- 4. Spin-on shape: the closing member rotates around an axis outside the valve seat.
- 5. disc-shaped: the closing member is a disc, rotating around a shaft inside the valve seat.
- 6. Sliding valve shape: the closing member slides in the direction perpendicular to the passage.
Third, according to the use, according to the different uses of the valve can be divided into.
- 1. Open and shut off: used to connect or cut off the pipeline medium, such as globe valves, gate valves, ball valves, butterfly valves, etc.
- 2. Check: used to prevent the backflow of media, such as check valves.
- 3. Adjustment: used to adjust the pressure and flow of the medium, such as regulating valves, pressure reducing valves.
- 4. Distribution: used to change the direction of media flow, distribution of media, such as three-way plug, distribution valve, slide valve, etc.
- 5. Safety valve: in the media pressure exceeds the specified value, used to discharge excess media to ensure the safety of piping systems and equipment, such as safety valves, accident valves.
- 6. Other special purposes: such as traps, air release valves, drain valves, etc.
Fourth, according to the drive mode, according to the different drive modes can be divided into.
- 1. Manual: with the help of handwheels, handles, levers or sprockets, etc., with human drive, transmission of larger torque is equipped with worm gears, gears and other reduction devices.
- 2. Electric: With the help of electric motors or other electrical devices to drive.
- 3. Hydraulic: with the help of (water, oil) to drive.
- 4. Pneumatic: driven by compressed air.
Fifth, by pressure, according to the nominal pressure of the valve can be divided into.
- 1. Vacuum valve: absolute pressure.
- 2. low pressure valve: nominal pressure PN ≤ 1.6Mpa valve (including PN ≤ 1.6MPa steel valve).
- 3. Medium pressure valve: nominal pressure PN2.5-6.4MPa valve.
- 4. High pressure valve: nominal pressure PN10.0-80.0MPa valve.
- 5. Ultra-high pressure valve: nominal pressure PN ≥ 100.0MPa valve.
Six, according to the temperature of the medium, according to the temperature of the medium when the valve works can be divided into.
- 1. Ordinary valves: valves for medium temperature -40 ℃ -425 ℃.
- 2. High temperature valves: applicable to the medium temperature 425 ℃ -600 ℃ valve.
- 3. Heat-resistant valves: applicable to the medium temperature of 600 ℃ or more valves.
- 4. Low temperature valves: applicable to the medium temperature -150 ℃ -40 ℃ valve.
- 5. Ultra-low temperature valves: applicable to the medium temperature -150 ℃ below the valve.
Seven, according to the nominal diameter points, according to the nominal diameter of the valve can be divided into.
- 1. Small diameter valves: nominal diameter < DN50 valves.
- 2. Medium diameter valves: nominal diameter DN50-300mm valves.
- 3. Large diameter valves: nominal diameter DN350-1200mm valves.
- 4. Extra large diameter valves: nominal diameter DN ≥ 1400mm valves.
Eight, according to the way of connection with the pipeline, according to the valve and the pipeline connection can be divided into.
- 1. Flange connection valve: valve body with a flange, and the pipeline flange connection valve.
- 2. Threaded connection valve: valve body with internal or external threads, and the pipeline using a threaded connection of the valve.
- 3. Welded connection valve: the valve body with a welded mouth, and the pipeline using a welded connection valve.
- 4. Clamp connection valve: the valve body with a clamp port, and the pipeline using a clamp connection valve.
- 5. Ferrule connection valve: the valve connected to the pipeline using a ferrule.
Gate valves are one of the most widely used of all types of valves in modern industry. In this type of valve, a gate-like plate in the valve body moves perpendicular to the fluid between the two seats with which it is mated, thus opening or cutting off the flow path. It is used as a shut-off and the entire flow path is straight through when fully open, when the medium operates with minimal pressure loss.
The general type of gate valve is usually suitable for work where it is not necessary to open and close frequently, and keep the gate fully open or fully closed. It is not suitable for use as regulation or throttling. For high-speed flow of media, the gate in the partially open state can cause vibration of the valve, and vibration may damage the gate and seat sealing surface, and throttling will cause the gate to suffer from media erosion.
The advantage is that the size between the two faces in the gate valve (the distance between the sealing surface and sealing surface of the valve) is smaller than that of the globe valve, etc. Therefore, when fully open, the flow becomes a linear relationship, and the pressure of the fluid is reduced.
The disadvantage is that it takes a certain amount of time to open and close, and the flat plate is at right angles to the direction of fluid flow, so when the ridge diameter increases, the pressure on the plate also increases, which will cause deformation of the plate and the valve body.
When using, it should be noted that from the installation point of view of the valve plate, it is not suitable for half-open state, but should be used for fully open or fully closed state.
Precautions for the use of the gate valve.
- 1. When the valve stem is opened and closed in place, no further force can be applied, otherwise the internal threads or latch screws will be pulled off and the valve will be damaged.
- 2. Open and close the valve when the hand can not be straight when open when the F wrench is available to open and close.
- 3. When opening and closing the valve, pay attention to the sealing surface of the valve, especially at the packing gland to prevent leakage.
Stop valve body shape although “jade”, so also known as jade valve. The structure is suitable for adjusting the flow, in most cases for the fully closed state.
The relatively short opening or closing stroke of the globe valve stem and its very reliable shut-off action make the globe valve ideal for cut-off or regulation and throttling.
Once the valve flap is removed from the closed position, there is no more contact between the valve seat and the sealing surface of the valve flap, thus its sealing surface mechanical wear is very small, as most of the globe valve seat and flap is relatively easy to repair or replace, and in the repair or replacement of sealing elements without disassembling the entire valve from the pipeline, which is very suitable for the valve and pipeline welded together. Thus, any wear that may occur during operation is not a major problem for this valve.
The minimum flow resistance of the globe valve is also higher than most other types of valves due to the change in the direction of flow of the medium through this type of valve. Then, depending on the valve body structure and the layout of the stem relative to the inlet and outlet channels, this condition can still be improved.
Precautions for the use of globe valves.
- 1. Check the valve for defects before opening, specifically the packing culvert for leakage;,.
- 2. When the valve stem cannot be rotated by hand, a special F wrench can be used to open and close it, and when it still cannot be opened and closed, please do not extend the wrench force arm to force it open and close, thus causing damage to the valve or causing safety accidents.
- 3. In the medium pressure steam line valve, open the condensate in the pipe should be drained, and then slowly open the valve with 0.2 to 0.3Mpa of steam to warm up the pipeline, to avoid a sudden increase in pressure caused by damage to the sealing surface, when the inspection is normal to adjust the pressure to the required state.
Check valves are also known as backflow valves, backpressure valves and flap valves. The use of the term “backflow” refers, within certain limits, to the swing valve type valve; the term “check” refers mainly to the lift valve type valve. The current use of the term “check valve”, which includes swing and lift type two types.
The role of the check valve is to allow the medium to flow in one direction only, and to prevent the flow in the opposite direction. Usually this valve is automatic work, in one direction of flow of fluid pressure, the valve flap open; fluid flow in the opposite direction, the fluid pressure and the weight of the valve flap so that the valve flap act on the valve seat, thereby cutting off the flow.
Notes on the use of check valves.
Pay attention to the direction of the valve, the arrow and the media flow direction, such as media easy to crystallize may cause the valve piece can not be pressed down to play a commanding, non-return role.
Plug valve is developed from the simple “Cork”. It has a conical or cylindrical plug body, the plug body can rotate, so that its channel relative to the valve body channel position change, so as to control the flow. The valve consists of only a few parts and is simple and compact. And it operates quickly, with only one right angle turn from fully open to fully closed plug. Since the medium can pass directly through the valve cavity with no abrupt changes in shape or cross-section, the valve’s therefore the valve’s losses are minimal.
An important feature of the plug valve is that it is easily adaptable to multi-channel configurations, so that one valve can obtain two, three, or even four different flow channels. This simplifies the set-up of piping systems and reduces the number of connections needed in some valves and equipment.
It is composed of a spigot and a valve body and is characterized by:
- ① The handle rotates 90″, and can be fully closed or fully opened.
- ② The flow path is a straight line, very almost slippery.
Its disadvantages are:
- ① Since the sealing surface is large, the sealing performance is poor.
- ② Handle operation is heavy, so in order to eliminate this shortcoming, the sealing surface is often coated with lubricating oil, forced lubrication.
Plug operation is convenient, for water, air, gas, etc., room temperature, atmospheric pressure pipeline.
The use of plug valve precautions.
- 1. The outer end of the valve stem is square, the diagonal marked straight line perpendicular to the direction of the valve body for the closed state, the same direction as the valve body for the open state.
- 2. Normal opening and closing of the valve with a special wrench from Coker to avoid safety accidents caused by slipping with the valve stem; try not to use an active wrench thus causing slippage.
- 3. Open the valve according to the previous inspection items, check and slowly open the valve after the inspection, try not to stand in the direction of the sealing surface when opening, and wear an acid mask when encountering acid and alkali fluids.
- 4. If the pipeline has a sight glass, see the fluid through the sight glass before the inspection is correct and leave.
The valve spool is a sphere, so it is called ball valve.
The ball valve is evolved from the plug valve. It has the same rotation 90° action and has the same rotating parts that are often in contact with the seal seat. The plunger is spherical and has a circular through-hole or passage through its axis. The ratio of the spherical surface to the passage opening should be such that when the ball is rotated 90°, it should show all spherical surface at the inlet and outlet, thus cutting off the flow.
The ball valve needs to be closed tightly with only 90° of rotation for operation and a very small turning torque. The completely parallel valve body cavity provides a flow path with little resistance and straight through for the medium. Even with a reduced bore, the pressure drop through the valve remains small. Therefore, from an economic point of view, most ball valves today already use indentations. The most common exception is valves required on lines cleared by “cleaners”.
Ball valves are generally considered to be best suited for direct opening and closing, but recent developments have designed them to throttle and control flow.
Notes on the use of ball valves.
a) The same as the plug valve.
b) with a handle valve, the handle is perpendicular to the direction of media flow for the closed state, and the same direction for the open state.
c) If you encounter a ball valve with jacket insulation should pay attention to the following matters.
- i. should be jacketed insulation steam to open the valve will be easy to crystallize the medium melting before opening and closing the valve, do not open and close the valve forcibly before the medium is completely melted.
- ii. When it comes to the valve can not open, you can not use the method of lengthening the force arm, forcibly open the valve, because this will cause damage to the valve or cause damage to the wrench due to the greater resistance to the stem and spool off, thus causing unsafe factors.
The name of butterfly valve comes from the wing-like structure of the butterfly plate, which is installed in the direction of the diameter of the pipe. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis by only 90° to open and close the valve.
The butterfly valve is simple in structure, small in size and light in weight. It consists of only a few parts. And it can be opened and closed quickly by rotating only 90°, which is easy to operate. The valve has good fluid control characteristics.
When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body. Therefore, the pressure drop through the valve is very small. In the valve closing motion, the butterfly plate rotates toward the closing position and the media flow velocity gradually decreases. The valve has good flow control characteristics.
Notes on the use of butterfly valve.
- 1. The spool can only rotate 90 degrees, the same as the valve body will indicate the direction of CLOSE and OPEN arrows, handwheel clockwise rotation for closing, and vice versa for opening.
- 2. If sometimes there is a certain resistance to open and close, you can use a special F wrench to open the valve, but can not be forced to open and close, otherwise the valve stem gear will be stirred bad.
- 3. Prohibit the handwheel to remove the active wrench to trigger the valve stem; (the same for the following valves)
- 4. Open and close gradually to see if there is a special situation, to prevent leakage.
Diaphragm valve is composed of the valve housing and the diaphragm equivalent to the spool, its operating mechanism is to rely on the movement of the diaphragm. There is a seal seat in the middle of the valve housing, and the diaphragm is operated by a handwheel to open and close the flow path by rising or falling.
The internal structure of the valve body is very simple, the inner surface of the valve body is often lined with glass, enamel, synthetic resin, rubber, etc., and the diaphragm is lined with rubber and synthetic resin. This type of valve is suitable for corrosive fluids because of the smooth flow path.
Safety valves are automatic protection valves in combustion or non-combustion pressure vessels and pipeline systems that exceed the safety pressure.
Safety valves or relief valves should be used on closed vessels or installations where the pressure is not at atmospheric pressure and where the pressure of the system may exceed the design pressure under certain circumstances. In some processes, such as media flow rate imbalance or energy input or output processes can cause the pressure of the device to exceed the operating pressure. If, for these or other reasons, the pressure exceeds the specified limit, then it must be depressurized by means of a safety valve or relief valve.
Precautions for the use of safety valves.
- 1. The use of safety valves must be within the validity period.
- 2. Pipeline, equipment installed on the safety valve manipulation valve is usually a shut-off valve must be open to ensure that the safety valve can work effectively.
- 3. Periodically lift the valve disc slightly, with the medium to blow clean valve impurities.
- 4. If the safety valve can not work within the set pressure, must be re-validated or replaced.
The working principle of safety valve
Safety valve is a safety device to prevent pressure equipment and containers or easy to cause pressure rise or pressure inside the container exceeds the limit and burst. Safety valve is a widely used safety device for pressure vessels, boilers, pressure piping and other pressure systems to ensure the safe operation of the pressure system.
When the pressure of the vessel exceeds the design, the safety valve automatically opens to discharge gas to reduce the excessive high pressure inside the vessel to prevent damage to the vessel or pipeline. And when the pressure in the container down to the normal operating pressure, that is automatically closed to avoid the container overpressure discharge of all the gas, thus causing waste and production interruption. The safety valve is composed of three parts: the valve seat, the valve spool and the loading mechanism. Valve seat and the valve body is a whole, some are assembled with the valve body, it is connected to the equipment. The valve flap is often attached with a valve stem, which is fastened to the valve seat. Above the valve flap is the loading mechanism, the size of the load can be adjusted. When the pressure in the device within a certain working pressure range, the internal medium acting on the valve flap above the force is less than the loading mechanism on the valve above the force, the difference between the two constitutes the sealing force between the valve flap and the valve seat, so that the valve flap is tightly pressed against the valve seat, the device can not discharge the medium. When the pressure inside the equipment exceeds the specified working pressure and reaches the opening pressure of the safety valve, the internal medium acting on the top of the flap is greater than the force exerted on it by the loading mechanism, so the flap leaves the valve seat, the safety valve opens, the medium inside the equipment is discharged through the valve seat, if the discharge volume of the safety valve is greater than the safety discharge volume of the equipment, the pressure inside the equipment that gradually decreases, and through a short period of time after the exhaust, the pressure is reduced back to normal working pressure. Now the internal pressure acting on the valve flap above the force is less than the force exerted on it by the loading mechanism, the valve flap and pressed against the valve seat, the media stopped discharging, the equipment to maintain the normal working pressure continuous operation. Therefore, the safety valve is through the media force on the valve flap and the loading mechanism of the force of the wax and wane, self-closing or opening to prevent the purpose of overpressure equipment.
Pressure reducing valve
Pressure reducing valves are installed in situations where the pressure needs to be reduced from one level to another, and they allow the outlet side to maintain a reduced pressure value within a specified range, independent of pressure fluctuations and flow changes at the inlet side. Pressure reducing valves are valves that work automatically.
Throttle valve, also known as needle valve, is similar in appearance to the globe valve, its spool shape is different, conical or parabolic, commonly used in the chemical appearance, often threaded connection.
The use of throttle valve precautions.
- 1. Because of the threaded connection, so when opening and closing the first check whether the threaded connection is loose leakage.
- 2. Open and close the valve slowly, because its flow area is small, the flow rate is large, may cause corrosion of the sealing surface, should keep an eye on the watch, pay attention to the change in pressure.
Size of the valve
It is well known that the size of the valve bore and the size of the pipe have an inevitable link, usually said how big the pipe diameter (internal diameter) with how big the valve. The valve caliber needs to be calculated according to the actual parameters, generally speaking, the pipeline will be larger, the actual valve to be smaller, depending mainly on the valve position needs to control the flow size is how much, and the pipe size only needs to flow capacity enough on the line.
Table.1-1 Valve diameter (DN) and pipe diameter size comparison table
|Comparison between pipe fitting size and valve diameter and inch:||Valve diameter DN (nominal diameter) corresponds to pipe outer diameter Ф (mm):|
|Diameter Inches||DN drift diameter (mm)||Outer diameter of pipe (mm)||Nominal diameter (DN)||Pipe OD Ф (Small outer diameter)||Pipe OD Ф (Large outer diameter)|
What is the pressure rating of the valve?
Usually, the kilogram pressure valve is equivalent to the Mpa, which is the conversion of the corresponding Mpa and kilogram, for example, 1.0MPa=10kg, 2.5MPa=25kg pressure.
Valve pressure conversion:
PN and CLass are both a way to express the pressure in the valve. The difference is that the pressure they represent corresponds to different reference temperatures. PN European system refers to the corresponding pressure at 120 ℃, while CLass American standard refers to the corresponding pressure at 425.5 ℃. Therefore, in engineering interchange, it is not allowed to simply convert the pressure. For example, the pressure conversion of CLass300 # should be 2.1MPa, but if the use temperature is considered, the corresponding pressure will increase. According to the temperature withstand test of the material, it is equivalent to 5.0MPa.
Valve pressure division:
National standard, American standard, Japanese standard valve nominal pressure, pound (Lb), megapascal (Mpa), bar, Japanese standard (K) conversion table.
|Comparison Table for Conversion of Pressure Grade pounds (Lb) and megapascals (Mpa)|
|Conversion Comparison Table of Pressure Grade Mpa and Bar|
|Comparison Table of Scale (Lb), Japanese Standard (K) and Nominal Pressure Conversion|
|Nominal pressure (MPa)||2||5||6.8||10||15||25||42|
What is the classification of valve standards?
The valve products are widely used in petroleum, chemical industry, nuclear power, metallurgy, electric power, water power, large coal chemical industry and other industries. With the continuous increase of the total amount of valve products, the continuous development of valve technology, and the continuous expansion of valve application fields, the corresponding valve standards are increasingly showing their importance. National standardization organizations have formulated relevant standards in the production and manufacturing process of valves. At present, the most widely used standards are BS (UK), DIN (Germany), JIS (Japan) and ISO (International Organization for Standardization). Although American standards organizations have been working hard to publish American standards in cooperation with other national standards to meet the requirements of internationalization, almost no standard can well cross national borders. When selecting standards, there are more or less conflicts between traditional American standards and ISO valve standards. This paper introduces the main valve standard organizations in the United States, and analyzes the causes of their conflicts.
The serial number of the standard generally consists of three parts: the standard code, the digital number (registration serial number) and the year of approval. The standard code indicates the level and scope of application of the standard.
1. Chinese standard code
|Standard code||Name||Standard code||Name|
|GB||National standard||HB||Ministry of Aviation Industry Standards|
|GB/T||National Recommended Standard||QJ||Ministry of Aerospace Industry Standards|
|GBn||National Standards (Internal Issue)||QB, SG||Ministry of Light Industry Standards|
|JB||National Military Standard||JZ, JG||Standard of the Ministry of Urban and Rural Environmental Protection|
|ZB||Industry Standard (Professional Standard 0||CB||Standard of China Shipbuilding Corporation|
|ZB||Industry Standard (Internal Release)||LD||Ministry of Labor and Personnel Standards|
|BYZGR||Professional Military Standard||JC||National Building Materials Bureau Standard|
|JB||Machinery industry standard||JJC||National Bureau of Metrology Standards|
|JB/Z||(Formerly) Guiding Document of the Ministry of Machinery Industry||CAS||Standards of China Standardization Association|
|EJ||(Formerly) Ministry of Nuclear Industry Standards||CVA||China valve industry standard|
|YB||Ministry of Metallurgical Standards||Q/TH||(Original) Professional Standards for Chemical General Machinery of the Ministry of Machinery Industry|
|HG||Ministry of Chemical Industry Standard||JB/TQ||The internal standard of the general machinery industry of the Ministry of Machinery and Electronics Industry|
|Sy||(Original) Ministry of Petroleum Standards||h||General design standard for high-pressure pipes, pipe fittings and fasteners|
|SD||Department of Hydropower Standards||ZB||Valve industry (professional) standard|
|MT||Ministry of Coal Industry Standard|
2. Foreign standard codes
|Standard code||Name||Standard code||Name|
|ISO||international standard||NBN||Belgian National Standard|
|ANSI||American National Standard||SIS||Swedish national standard|
|BS||British National Standards||SNU||Swiss National Standard|
|DIN||German national standard||ASTM||ASTM standard|
|NF||French national standard||AISI||American Iron and Steel Institute Standard|
|JIS||JIS||APIs||American Petroleum Institute Standard|
|FOCT||National Standards of the Former Soviet Union||MSS||American Valve and Fitting Manufacturers Standardization Association Standards|
|ASME||American Society of Mechanical Engineers Standard||AWS||American Welding Society Standard|
|CSA||Canadian National Standard||ASI||American Specification Association Standard|
|DS||Danish national standard||MIL||Cabinet Military Standards|
|NEN||Dutch national standard||JPI||Japan Petroleum Institute Standard|
What are the types of valve sealing surfaces?
One of the most widespread uses of valves in pipelines and equipment is to cut off the flow of media. And because the valve in the process of use, its sealing surface is subject to long-term media erosion and corrosion, but also the existence of sealing than the role of friction and wear between the sealing vice, so the working conditions are quite harsh. Therefore, the sealing of the valve is the main factor to decide whether to produce internal leakage or not.
The sealing surface of the valve is generally composed of a pair of seals, one on the valve body and the other on the valve flap, and the sealing form of the internal seal according to the surface geometry of the sealing surface, the sealing type of the valve seal can be distinguished as follows:
Valve sealing form
One or two of the contact surfaces are spherical, with good sealing effect, even if the valve flap is slightly offset, it will not affect the performance of the sealing surface of the valve seat. However, the sealing surface is more difficult to process than the flat seat and tapered seat. (a) The figure shows the ball sealing surface, which is used on the sealing surface of valves such as ball valves and safety valves. (b) Figure shows the spherical sealing surface, used on the sealing surface of valves with small bore.
Circular arc face seal
One of the pair of sealing surfaces of its seal is circular arc face, which has good sealing effect, but is difficult to process and maintain. (a) The diagram shows the circular arc face sealing surface, which is mainly used in ammonia valves. (b) Figure is the “O’, shaped ring sealing surface, mainly used in parallel single gate gate valve, butterfly valve and other valve sealing surface.
Knife-shaped sealing surface
There is a knife-like sealing surface in a pair of sealing surfaces. Because the sealing surface cannot withstand too much closing force, it is mainly used in vacuum valves and cases where the closing force is not large.
The sealing surface is a pair or two pairs of flat surfaces in contact. Pure plane seal form, the valve seat surface is easy to contact, the surface pressure is also very stable, but requires the stem to apply a large closing force on the sealing surface, not suitable for high-pressure use, this form of sealing surface is commonly used in the globe valve
The sealing surface is a pair of contact cone surface. Its contact area is small, easy to seal and effective. Because the valve seat has a taper, the pressure on it is greater than the flat seal, which is conducive to preventing media leakage. However, because of the high pressure on the sealing surface of the seat, so the hard seat such as stainless steel must be properly heat-treated to make the sealing surface of the seat with high hardness; or overlay welding of Stearic heat-resistant and wear-resistant hard alloy; or quenching treatment of the sealing surface. (a) The diagram shows the tapered seal, mostly used on general-purpose valves. (b) The diagram shows the needle-shaped sealing surface, which is only used for needle-shaped globe valves. (c) The diagram shows the cone sealing surface, such as the sealing surface of the plug valve is this structure.
The preparation method of the valve model
Valve model should usually indicate the valve type, drive mode, connection form, structural features, nominal pressure, sealing surface material, valve body material and other elements. The standardization of the valve model provides convenience to the design, selection and distribution of valves.
Today, the types of valves and materials are more and more diverse, and the preparation of valve models is becoming more and more complex. Although China has a unified standard for the preparation of the valve model, but more and more can not adapt to the needs of the valve industry development. At present, valve manufacturers generally use a unified numbering method; where more and more can not adapt to the needs of the development of the valve industry. At present, valve manufacturing plants generally use a unified numbering method; where a unified numbering method can not be used, the production plants are developed according to their own situation numbering method.
JB308-75 “Valve Modeling Method” applies to industrial pipeline gate valves, globe valves, throttle valves, ball valves, butterfly valves, diaphragm valves, plug valves, check valves, safety valves, pressure reducing valves, steam traps. It includes the type preparation of the valve and the naming of the valve.
The model number of the valve consists of 7 units, whose meanings are shown below.
There are many materials for manufacturing valve parts, including a variety of different grades of ferrous and non-ferrous metals and their alloys, various non-metallic materials, etc.. The material for manufacturing valve parts should be selected according to the following factors.
- The pressure, temperature and characteristics of the working medium.
- The part of the force and the role played in the valve structure.
- There is a good process.
- In the case of meeting the above conditions, to have a low cost.
Valve body, valve cover and valve plate (valve flap) materials
Gray cast iron: gray cast iron for nominal pressure PN ≤ 1.0MPa, the temperature of -10 ℃ -200 ℃ of water, steam, air, gas and oil and other media. Gray cast iron commonly used grades: HT200, HT250, HT300, HT350.
Malleable cast iron: suitable for nominal pressure PN ≤ 2.5MPa, the temperature of -30-300 ℃ water, steam, air and oil media, commonly used grades: KTH300-06, KTH330-08, KTH350-10.
Ductile iron: suitable for PN≤4.0MPa, the temperature is -30-350 ℃ water, steam, air and oil and other media. Commonly used grades are: QT400-15, QT450-10, QT500-7.
Carbon steel (WCA, WCB, WCC): for nominal pressure PN ≤ 32.0MPa, for the working temperature between -29 ~ +425 ℃, medium and high pressure valves, including 16Mn, 30Mn working temperature of -29-595 ℃, commonly used to replace ASTM A105. commonly used grades are WC1, WCB, ZG25 and high quality steel 20, 25, 30 and low alloy structural steel 16Mn. 30 and low alloy structural steel 16Mn.
Low-temperature carbon steel (LCB): for nominal pressure PN ≤ 6.4Mpa, temperature ≥ -196 ℃ ethylene, propylene, liquid natural gas, liquid nitrogen and other media, commonly used grades ZG1Cr18Ni9, 0Cr18Ni9, 1Cr18Ni9Ti, ZG0Cr18Ni9.
Alloy steel (WC6, WC9), applicable to the working temperature between -29-595 ℃ non-corrosive media of high temperature and high pressure valves; WC5, WC9 applicable to the working temperature between -29-650 ℃ corrosive media of high temperature and high pressure valves.
Austenitic stainless steel, suitable for the working temperature between -196-+600 ℃ corrosive media valves.
Monel alloy: mainly applicable to hydrogen and fluorine media valves.
Cast copper alloy: mainly applicable to the working temperature between -29-595 ℃ oxygen pipeline with the valve.
Common materials of valve shell
|Shell material||Standard||Applicable temperature/℃||Applicable pressure/MPa||Applicable media|
|Grey cast iron||-15–200||≤1.6||Water and gas|
|Black core malleable iron||-15–300||≤2.5||Water, sea water, gas, ammonia|
|Ductile iron||-30–350||≤4.0||Water, sea water, gas, Air, steam|
|Carbon steel (WCA, WCB, WCC)||ASTM A216||-29–425||≤32.0||Non corrosive applications, including water, oil and gas|
|Low temperature carbon steel (LCB, LCC)||ASTM A352||-46–345||≤32.0||Low temperature application|
|Alloy steel (WC6, WC9)||ASTM A217||-29–595||High pressure||Non corrosive medium|
|（C5, C12）||-29–650||Corrosive medium|
|Austenitic stainless steel||ASTM A351||-196–600||Corrosive medium|
|Monel||ASTM A494||400||Fluorine s medium containing hydrogen|
|Hastelloy||ASTM A494||649||Strong corrosive medium such as dilute sulfuric acid|
|Titanium alloy||Various strong corrosive media|
|Cast copper alloy||-273–200||Oxygen, seawater|
|Plastics, ceramics||–60||≤1.6||Corrosive medium|
|Code||Material||Standard||Applicable conditions||Temperature range|
|WCB||Carbon steel||ASTM A216||Non corrosive applications, including water, oil and gas||-29℃-+425℃|
|LCB||Low temperature carbon steel||ASTM A352||Low temperature application||-46℃-+345℃|
|LC3||3.5% nickel steel||ASTM A352||Low temperature application||-101℃-+340℃|
|WC6||1.25% Cr 0.5% Mo steel||ASTM A217||Non corrosive applications, including water, oil and gas||-30℃-+593℃|
|C5||5% Cr 0.5% Mo||ASTM A217||Mild corrosive or aggressive applications and non corrosive applications||-30℃-+649℃|
|C12||9% Cr 1% Mo|
|CA15||12% chromium steel||ASTM A217||Corrosive Applications||+704℃|
|CA6NM||12% chromium steel||ASTM A487||Corrosive Applications||-30℃-+482℃|
|CF8M||316 stainless steel||ASTM A351||Corrosive or ultra low or high temperature non corrosive applications||-268 ℃ to+649 ℃, and 0.04% or more carbon content shall be specified above 425 ℃|
|CF8C||347 stainless steel||ASTM A351||Mainly used for high temperature and corrosive applications||-268 ℃ to+649 ℃, and 0.04% or more carbon content shall be specified above 540 ℃|
|CF8||304 stainless steel||ASTM A351||Corrosive or ultra low or high temperature non corrosive applications||-268 ℃ to+649 ℃, and 0.04% or more carbon content shall be specified above 425 ℃|
|CF3||304L stainless steel||ASTM A351||Corrosive or non corrosive applications||+425℃|
|CF3M||316L stainless steel||ASTM A351||Corrosive or non corrosive applications||+454℃|
|CN7M||Alloy steel||ASTM A351||It has good resistance to hot sulfuric acid corrosion||+425℃|
|M35-1||Monel||ASTM A494||Weldable grade. It has good corrosion resistance to all common organic acids and salt water. It also has high corrosion resistance to most alkaline solutions||+400℃|
|N7M||Hastelloy B||ASTM A494||It is especially suitable for hydrogen fluoride s of various concentrations and temperatures of the processor. It has good corrosion resistance to sulfuric acid and phosphoric acid||+649℃|
|CW6M||Hastelloy C||ASTM A494||It has good corrosion resistance to strong oxidation environment. It has good properties under high temperature, and has high corrosion resistance to formic acid (formic acid), phosphoric acid, sulfite and sulfuric acid||+649℃|
|CY40||Inconel||ASTM A494||It performs well in high temperature applications. It has good corrosion resistance for strong corrosive fluid medium|
Material of sealing surface
The sealing surface is the most critical working surface of the valve, and the quality of the sealing surface is related to the service life of the valve. Generally, the sealing surface materials should consider corrosion resistance, abrasion resistance, erosion resistance, oxidation resistance and other factors. There are usually two categories:
(1) Soft material
- 1. Rubber (including butadiene rubber, fluororubber, etc.)
- 2. Plastic (PTFE, nylon, etc.)
(2) Hard sealing material
- 1. Copper alloy (for low pressure valve)
- 2. Chrome stainless steel (used for ordinary high and intermediate pressure valves)
- 3. Stellite alloy (used for high-temperature and high-pressure valves and strongly corrosive valves)
- 4. Nickel base alloy (for corrosive medium)
Material of valve stem
During the opening and closing process of the valve, the valve stem bears the tensile, compressive and torsional forces, and is in direct contact with the medium. At the same time, there is a relative friction movement between the valve stem and the packing. Therefore, the valve stem material must have sufficient strength and impact toughness at the specified temperature, a certain degree of corrosion resistance and scratch resistance, and good processability. The commonly used valve stem materials are as follows.
When it is used for water and steam medium with low pressure and medium temperature not exceeding 300 ℃, A5 ordinary carbon steel (Q275, Q235 for A3) is generally selected.
For medium pressure and water and steam medium with medium temperature not exceeding 450 ℃, 35 high-quality carbon steel is generally selected.
40Cr is generally used for medium pressure and high pressure water, steam, oil and other media with medium temperature not exceeding 450 ℃ (Chrome steel).
38CrMoALA nitriding steel can be selected when it is used for water, steam and other media with high pressure and medium temperature not exceeding 540 ℃.
25Cr2MoVA chrome molybdenum vanadium steel is generally used for steam medium with high pressure and medium temperature not exceeding 570 ℃.
Stainless acid resistant steel
1Cr13, 2Cr13, 3Cr13 chromium stainless steel can be used for medium pressure and high pressure non corrosive medium and weak corrosive medium with medium temperature not exceeding 450 ℃.
When used in corrosive medium, stainless acid resistant steel such as Cr17Ni2, 1Cr18Ni9Ti, Cr18Ni12Mo2Ti, Cr18Ni12Mo3Ti and PH15-7Mo precipitation hardening steel can be selected.
Heat resistant steel
When used for high temperature valves with medium temperature not exceeding 600 ℃, 4Cr10Si2Mo martensitic heat-resistant steel and 4Cr14Ni14W2Mo austenitic heat-resistant steel can be selected.
Material of stem nut
Stem nut in the valve opening and closing process, directly bear the stem axial force, so must have a certain strength. At the same time it is threaded transmission with the valve stem, requiring a small coefficient of friction, no rust and avoid bite phenomenon.
Copper alloy has a small coefficient of friction and does not rust, so it is one of the commonly used materials. For Pg<1.6Mpa low pressure valves can be ZHMn58-2-2 cast brass. For Pg16-6.4Mpa medium-pressure valves, ZQAL9-4 Wuxi bronze can be used. For high pressure valves, ZHAL66-6-3-2 cast brass can be used.
When the working conditions do not allow the use of copper alloy, can use 35, 40 and other high-quality carbon steel, 2Cr13, 1Cr18Ni9, Cr17Ni2 and other stainless acid-resistant steel. The working conditions do not allow the following conditions.
- Used on electric valves, with melon clutch stem nut, need to heat treatment to obtain high hardness or surface hardness.
- When the working medium or the surrounding environment is not suitable for the selection of copper alloy, such as the ammonia medium which is corrosive to copper.
Valve pressure test method
In general, industrial valves in use without strength test, but after repairing the valve body and cover or corrosion damage to the valve body and cover should do strength test. For the safety valve, its rectification pressure and back to the seat pressure and other tests should be in accordance with its instructions and the provisions of the relevant regulations. Valve installation should be strength and sealability test. Low-voltage valve spot check 20%, such as failure should be 100% of the inspection; medium and high pressure valves should be 100% of the inspection. Valve test pressure commonly used media are water, Oil, Air, steam, nitrogen, etc., various types of industrial valves including pneumatic valves test pressure methods are as follows.
Ball valve test pressure method
Pneumatic ball valve strength test should be carried out in the ball half-open state.
① Floating ball valve sealing test: the valve in a half-open state, one end of the introduction of the test medium, the other end closed; the ball will be rotated several times, the valve is closed when the closed end of the open check, while checking the packing and gasket at the sealing performance, there shall be no leakage. Then introduce the test medium from the other end and repeat the above test.
② Fixed ball valve sealing test: before the test will be idle ball rotation several times, fixed ball valve in a closed state, from one end of the introduction of the test medium to the specified value; using a pressure gauge to check the sealing performance of the introduction end, the use of pressure gauge accuracy 0.5-1 level, the range of the test pressure 1.5 times. In the specified time, no pressure drop phenomenon for qualified; and then introduce the test medium from the other end, repeat the above test. Then, the valve in a half-open state, both ends closed, the cavity is filled with media, check the packing and gasket at the test pressure, there shall be no leakage.
③ Three-way ball valve should be tested in each position for tightness.
Check valve test pressure method
Check valve test state: lift type check valve valve flap axis is in a vertical position with the horizontal; swing type check valve channel axis and flap axis is in a position approximately parallel to the horizontal line.
Strength test, the introduction of test media from the inlet end to the specified value, the other end closed, see the valve body and valve cover no leakage for qualified.
The sealing test is qualified by introducing the test medium from the outlet end, checking the sealing surface at the inlet end, and no leakage at the packing and gasket.
Pressure reducing valve test method
① Strength test of pressure reducing valve is generally assembled after single piece test, or assembled after test. Duration of strength test: DN<50mm for lmin; DN65-150mm for more than 2min; DN>150mm for more than 3min. After welding of bellows and components, 1.5 times of the highest pressure after applying pressure reducing valve and strength test with air.
② Sealability test according to the actual working medium. With air or water test, 1.1 times the nominal pressure for the test; with steam test, the highest working pressure allowed under the working temperature. The difference between the inlet pressure and the outlet pressure is not less than 0.2 MPa. The test method is: after the inlet pressure is set, gradually adjust the adjusting screw of the valve so that the outlet pressure can change sensitively and continuously within the maximum and minimum values, without stagnation and blocking. For steam pressure reducing valve, when the inlet pressure is adjusted away, close the valve after the cut-off valve, the outlet pressure is the highest and lowest value, and within 2min, the rise of its outlet pressure should be in accordance with the provisions of Table 4.176-22, and at the same time, the volume of the pipeline after the valve is in accordance with the provisions of Table 4.18 as qualified; for water and air pressure reducing valve, when the inlet pressure is adjusted and the outlet pressure is zero, close the Pressure reducing valve for sealing test, no leakage in 2min for qualified.
Butterfly valve pressure test method
The strength test of the pneumatic butterfly valve is the same as that of the globe valve. Butterfly valve sealing performance test should be introduced from the media flow end of the test medium, the butterfly plate should be opened, the other end closed, inject pressure to the specified value; check the packing and other sealing place no leakage, close the butterfly plate, open the other end, check the butterfly plate sealing place no leakage for qualified. The butterfly valve used for regulating the flow may not do the sealing performance test.
Test pressure method of plug valve
① When the strength test of the plug valve, the medium is introduced from one end, close the rest of the pathway, rotate the plug in turn to the full open working position for the test, the valve body is not found to be leaking as qualified.
② Sealing test, straight-through plug should keep the cavity and access pressure equal, the plug will be rotated to the closed position, from the other end to check, and then rotate the plug 180 ° to repeat the above test; three-way or four-way plug valve should keep the cavity and access pressure equal at one end, the plug will be rotated to the closed position in turn, the pressure is introduced from the right-angle end, from the other end to check at the same time.
Plug valve test before allowing a layer of non-acidic thin lubricant on the sealing surface, no leakage and expanding water droplets found in the specified time for qualified. Plug valve test time can be shorter, generally according to the nominal diameter of the provisions of l-3min.
Plug valve for gas should be 1.25 times the working pressure for air tightness test.
Diaphragm valve pressure test method
Diaphragm valve strength test from either end of the introduction of the medium, open the valve flap, the other end closed, test pressure up to the specified value, see the valve body and valve cover no leakage for qualified. Then lower the pressure to the sealing test pressure, close the valve flap, open the other end for inspection, no leakage for qualified.
Test pressure method of stop valve and throttle valve
Strength test of stop valve and throttle valve, usually put the assembled valve in the pressure test frame, open the valve flap, inject medium to the specified value, check whether the valve body and valve cover sweat and leakage. Strength test can also be done for a single piece. Sealing test is done only for shut-off valves. Test the stem of the globe valve into a vertical state, the valve flap open, the media from the bottom end of the valve flap introduced to the specified value, check the packing and gasket; to be qualified to close the valve flap, open the other end to check whether there is leakage. If the valve strength and sealing test are to be done, the strength test can be done first, then lower the pressure to the specified value of the sealing test, check the packing and gasket; then close the valve flap, open the export end to check whether the sealing surface leakage.
Gate valve pressure test method
Gate valve strength test is the same as the globe valve. There are two ways to test the sealing of the gate valve.
① Gate open, so that the pressure in the valve to the specified value; then close the gate, immediately remove the gate valve, check whether there is leakage on both sides of the gate seal or directly to the plug on the valve cover to inject test media to the specified value, check the seal on both sides of the gate. The above method is called the intermediate test pressure. This method is not suitable for sealing test in the gate valve with nominal diameter below DN32mm.
② Another method is to open the gate, so that the valve test pressure up to the specified value; then close the gate, open one end of the blind, check whether the sealing surface leakage. Then reverse the head, repeat the above test until qualified. Pneumatic gate valve packing and gasket at the sealing test should be carried out before the gate sealing test.
Pressure test method of safety valve
① The strength test of the safety valve is the same as other valves, it is tested with water. When testing the lower part of the valve body, the pressure is introduced from the I = I end, the sealing surface is closed; when testing the upper part of the valve body and valve cover, the pressure is introduced from the El end, the other end is closed. In the specified time valve body and valve cover no leakage phenomenon for qualified.
② Sealing test and pressure test, the general use of media are: steam safety valve with saturated steam as the test medium; ammonia or other gases with the valve with air as the test medium; water and other non-corrosive liquids with the valve with water as the test medium. For some important positions of the safety valve commonly used nitrogen as the test medium.
Seal test to the nominal pressure value for the test pressure, the number of times not less than two, no leakage in the specified time for qualified. There are two methods of leak detection: one is to seal the connections of the safety valve, using butter to seal the thin paper paste in the out El flange, thin paper bulging for leakage, not bulging for qualified; second, using butter to seal the thin plastic plate or other plates in the lower part of the export flange, water seal valve flap, test water does not bubble for qualified. Safety valve pressure setting and back to the seat pressure test not less than 3 times, in accordance with the provisions of the qualified. Safety valve performance test see GB / T12242-1989 safety valve performance test methods.
The basic content of valve design
Valve as an important part of the piping system, should ensure the safe and reliable implementation of the piping system requirements for the use of valves. Therefore, the valve design must meet the pressure of the working medium, temperature, corrosion, fluid properties and operation, manufacturing, installation, maintenance and other aspects of the valve to put forward all the requirements.
Valve design must be clear given the technical data, that is, the “design input”, on the basis of which the design can be completed correctly.
Valve “design input” must have the following basic data:
- The purpose or type of valve;
- The working pressure of the medium;
- The medium’s working drawing;
- The physical and chemical properties of the medium (corrosiveness, flammability and explosivity, toxicity, physical state, etc.);
- Nominal through-put;
- Structure length;
- The connection form with the pipeline;
- Valve operation mode (manual, gear drive, worm gear drive, electric, pneumatic, hydraulic, etc.).
In the valve technical design and working drawing design, the data and technical requirements should be mastered.
- The flow capacity and fluid resistance coefficient of the valve;
- Valve opening and closing speed and opening and closing times;
- Drive device energy characteristics (AC or DC, voltage, air pressure, etc.);
- Valve working environment and its maintenance conditions (whether explosion-proof, whether tropical climate conditions, etc.);
- Limitations on dimensions;
- Weight limit;
- Earthquake resistance requirements.
Valve design procedures:
- Design and development planning;
- Design and Development Phases;
- Review, verification and validation activities appropriate for each design and development phase;
- Design and development responsibilities and authorities.
Design and Development Inputs:
- Functional and performance requirements;
- Legal and regulatory requirements for use;
- Information provided by previous similar designs;
- Other requirements necessary for design and development.
Design and Development Outputs:
- Meet the requirements of the design and development inputs;
- Gives appropriate information for procurement, production and service provision;
- Contains or references product acceptance criteria;
- Specify the product characteristics necessary for the safety and proper use of the product;
- Design and development confirmation confirms design and development changes by means of product qualification.
How are valves made?
At first glance, the valve parts are not many, simple structure, general precision, in the mechanical industry is a simple part, but the core sealing parts of the valve is particularly demanding. Valve manufacturing process is complex and technically difficult, which process characteristics we need to pay attention to?
The processing of cast valves
Casting valve manufacturing process
The first step: valve body manufacturing.
Valve body (casting, sealing surface overlay welding).
Casting procurement (according to the standard) → into the factory inspection (according to the standard) → surfacing groove → ultrasonic flaw detection (according to the drawings) → surfacing and post-welding heat treatment → finishing → grinding sealing surface? Seal surface hardness inspection, coloring flaw detection.
Step 2: Valve internal parts manufacturing process.
A. The need to weld the seal surface of the internal parts such as valve flap, valve seat, etc.
Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of billet (round steel or forgings, according to the drawing process requirements) → rough machining ultrasonic flaw detection surface (when the drawing requirements) → rough machining surfacing groove → surfacing and post-welding heat treatment? Finishing processing of each department? Grinding sealing surface? Seal surface hardness test, coloring flaw detection.
B. Valve stem
Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of rough (round steel or forgings, according to the drawing process requirements)? Rough machining surfacing groove → surfacing and post-welding heat treatment? Finishing ministries → Grinding outer circle → Stem surface treatment (nitriding, quenching, chemical plating) → Final treatment (polishing, grinding, etc.) → Grinding sealing surface → Seal surface hardness inspection, coloring flaw detection.
C. Internal parts that do not require overlay welding of sealing surface, etc.
Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of billet (round steel or forgings, according to the drawing process requirements) → rough machining ultrasonic flaw detection surface (when the drawing requirements) → finishing processing ministries.
Step 3: Fastener manufacturing.
Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → production of rough (round steel or forgings, according to the drawing process requirements) and sampling for the necessary inspection → rough machining → finishing → spectral inspection.
Step 4: General assembly.
Pick up parts → cleaning, cleaning → rough assembly (according to the drawings) → hydraulic test (according to the drawings, process) → after passing, disassembly, wipe clean → final assembly → with electric assembly or actuator commissioning (for electric valves) → paint packaging → shipping.
Step 5: Product production and inspection process.
- The raw materials of various specifications purchased by the company.
- Material testing of raw materials with spectral analyzer, and print out the material testing report of raw materials for backup.
- Cutting of raw materials with the lowering machine.
- Inspection personnel check the cutting diameter and length of raw materials.
- Forging workshop to forge the raw materials for forming treatment.
- Inspection personnel carry out various dimensional inspections on the forming of blanks.
- Workers are removing the waste edge of the blank.
- Sand blasting workers conduct surface sand blasting treatment on the blank.
- Inspection personnel carry out surface treatment inspection after sandblasting.
- Workers are machining the blank.
- Valve body sealing thread processing-employees in the processing of self-inspection inspectors to the product after the product for processing after inspection.
- Valve body connection thread processing.
- Middle hole processing.
- Inspection personnel for total inspection.
- The qualified semi-finished products are sent to the semi-finished products warehouse.
- Semi-finished products are plated.
- Semi-finished product plating surface treatment inspection.
- The inspection of various accessories (ball, stem, seal seat).
- Assembly workshop for product assembly – assembly line inspectors to inspect the product.
- The assembled products go to the next process after pressure test and drying.
- The final assembly workshop carries out product packaging – the packaging line inspector inspects the sealing, appearance and torque of the product. Unqualified products are never allowed to be packaged.
- Qualified products are bagged and packed and sent to the finished product warehouse.
- All the inspection records will be sorted and stored in the computer for reference at any time.
- The qualified products are sent to home and abroad by container.
Casting valve manufacturing process features
1. Manufacturing materials
Due to the wide variety of valve specifications, applied in various areas of the national economy, its use occasions vary widely, such as high temperature and high pressure, low temperature, deep cold, flammable and explosive, highly toxic, strong corrosive media and other working conditions, the valve material put forward harsh requirements.
In addition to cast iron, carbon steel, alloy structural steel, but also a large number of CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy and G0CrW carbide, etc.. The casting, welding and processing properties of these high-alloy materials are very poor, which makes the manufacturing process very difficult. Coupled with the fact that most of these materials are high alloy, high strength, high hardness precious materials, there are many difficulties in the selection, preparation and procurement from the materials. Some materials are difficult to procure and supply because of the small amount used.
2. Structure of casting blanks
Most of the valve blanks are thin shell castings with complex structure, which require not only good appearance quality, but also dense internal quality and good metallographic structure, without defects such as porosity, shrinkage, sand trapping and cracks. Therefore, the casting process is complex and the heat treatment technology is difficult. In the machinery industry, the valve pressure thin shell casting blank casting difficulty is far more complex than other mechanical components of the casting, more difficult.
3. Machining process
As most of the high strength, high hardness, high corrosion-resistant materials are not good cutting performance, such as high alloy stainless steel, acid-resistant steel have toughness, high strength, poor heat dissipation, chip viscosity and machining hardening tendency and other shortcomings, it is difficult to achieve the required dimensional accuracy and finish, to the machining of tools, processes and equipment to bring certain difficulties. In addition, the valve sealing surface in the machining accuracy, with the angle, finish and pairing the requirements of the seal is also very high, bringing great difficulty to machining.
4. Valve parts of the process arrangements
The main parts of the valve are few in number, the structure is relatively simple, most of the size of the machining accuracy is not high, the exterior is relatively rough, which gives the impression of a simple machine. In fact, the heart of the valve sealing parts but extremely precise, the sealing surface of the “three degrees” (flatness, finish, hardness) requirements are very high, as well as the two sealing surfaces composed of the sealing pair of coincidence should reach zero to zero, in order to meet the gas-tight test of zero leakage. This rough benchmark to ensure the heart of the precision of the zero-to-zero requirements, is the valve processing of the larger process difficulties.
5. Valve testing and inspection
Valve is an important pressure pipeline opening and closing, regulating components, and the use of pressure piping conditions are very different, high temperature and high pressure, low temperature, deep cold, flammable and explosive, highly toxic and strong corrosion. But the valve manufacturing test and inspection conditions are unlikely to meet the same requirements of the working conditions, international and domestic valve test standards are close to room temperature conditions, using gas or water as the medium for the test. This is a more fundamental pitfalls, is the normal factory test qualified valve products, in the harsh actual conditions may arise due to material selection, casting quality and sealing damage and other issues to meet the requirements of use, but also major quality accidents. No wonder some of the old pneumatic valve experts who have done a lifetime, the older the more restrained, the more dry the more worried.
The processing of forged valves
Forging, forging, forged steel valves are simply steel valves used for forging, forged steel refers to the use of forging methods and the production of a variety of forged materials and forgings. Forged steel parts valve quality is higher than cast steel parts, can withstand large impact force effect, plasticity, toughness and other aspects of mechanical properties are also higher than cast steel parts, so all some important machine parts should be used forged steel parts, forged steel is generally used for high-pressure pipelines. With a fine organization, suitable for high-pressure working conditions.
Forging is one of the two major components of forging, machinery, high load, severe working conditions of the important parts, more forgings, the shape of the simpler available rolled welded parts, except for the profile plate. Through forging can eliminate the metal material weld holes and cast looseness.
The correct choice of forging than to improve product quality, reduce costs have a great relationship. Forging materials are mainly carbon steel, stainless steel and alloy steel. Forging ratio is the ratio of the cross-sectional area of the metal before deformation and the die cross-sectional area after deformation. The original state of the material is ingot, bar, liquid metal and metal powder.
The mechanical properties of forgings are generally better than castings of the same material, forging is through forging machinery to apply pressure to the metal blank, so that the metal billet plastic deformation to obtain a certain shape and size and better mechanical properties of the processing method.
Forging, forging, forged steel valve structure process.
The quality and performance of the valve body directly affects the life of the valve operation and its safety. Therefore, in the case of valves working in harsh environments or with high requirements for their safety, forged valve bodies should be used. For DN50 below the gate valve, globe valve, check valve, etc., most of the domestic use of the overall forging and forming after welding the flange at both ends of the process, there are manufacturers even through the flange together forging molding. For more than 2 inch large-diameter valve body, due to the lack of forging forming the required heavy multi-directional forging equipment, to achieve localization of large overall forging parts and a certain degree of difficulty. Therefore, many manufacturers import large valve body forgings from abroad, or cooperate with some foreign companies to develop the use of forging and welding valve body parts.
Shear – squeeze forming new technology
A new technology using shear-extrusion forming, using the advantages of its energy-saving labor-saving, through the valve body forming process of experimental research, resulting in large forged steel valve body shear-extrusion forming process parameters.
The shear-extrusion forming process is a metal plasticity processing process mainly based on shear deformation. The basic mechanical characteristics of the forming process is to make the squeezing pressure of the large cap degree is reduced. This also greatly reduces the tonnage of the equipment required for the forming process. Valve body for shear-extrusion forming of the production process before the test study, the first t / 3 feet of the scaled parts for physical simulation studies, shear-extrusion forming reference process parameters, to develop the production process test parameters. Take the DN100 globe valve body process as an example, through the production process test research. The process parameters for shear-extrusion forming of DNlOOmm globe valve body made of 20 steel are as follows: heating temperature of rough specimen 1200℃, preheating of die 100-300℃. Graphite water agent is used as lubricant. The punch is conical and the diameter of the punch is about 108mm. 1000t press can meet the forming needs.
The forging and forming of large-diameter globe valve body is realized on small and medium-sized equipment, which verifies the energy-saving and labor-saving characteristics of the shear-extrusion forming process. The shear-extrusion forming process is energy-saving and labor-saving, and can be used to form large forged globe valve bodies on existing domestic equipment. In addition. The use of shear-extrusion forming technology, you can study the forging of tee tubes and other large branch and fork type parts.
Forging by forming method can be divided into:
- (1) Closed mode forging (die forging). Can be divided into die forging, rotary forging, cold heading, extrusion, etc., the metal billet in a certain shape of the forging die pressure deformation and obtain forgings. According to the deformation temperature is divided into cold forging (forging temperature is room temperature), warm forging (forging temperature is lower than the recrystallization temperature of the billet metal), hot forging (forging temperature is higher than the recrystallization temperature).
- (2) Open forging (free forging). There are manual forging and mechanical forging two ways, the metal billet placed on the upper and lower two anvil (against the iron) between the use of impact or pressure to deform the metal billet to obtain the required forgings.
Forging, forging, forging steel valve process improvement methods.
Need to use a special expansion head to assemble the valve in and out of the channel (channel diameter tolerance to be properly controlled) as a positioning reference, both ends of the expansion at the same time. Forged steel valve body rebound to make up for the amount greater than the amount of seat rebound, the valve body hole tightly wrapped around the seat, no gap, good sealing. Therefore, the axial load must be strictly controlled. When the valve seat pressure paste to the valve body, shall make the valve body wall in the elastic limit of deformation, to ensure that the expansion force disappears, the valve body wall springback, to make up for the seat springback, so that they are tight to each other, so to limit the maximum axial load.
To prevent excessive assembly stress exists, the forged steel valve seat tail material strength is not easy to high, good plasticity and low hardness, and control the assembly load. At the same time, in order to ensure that the seat pressure with a small amount of rebound, there should be enough displacement, and make the seat tail length is not less than twice its wall thickness. The use of “installed after the pressure” process, can ensure product quality, forged steel valve seat processing convenience, improve the efficiency of the assembly machine with.
The main parts of the valve metal processing process
A. The valve bo.dy, valve cover, valve flap (valve plate)
For DN ≥ 50 valves, valve body, valve cover using castings, DN < 50 using forgings. Valve before casting, the steel for pre-furnace sampling and analysis, when the chemical composition of the raw materials of the furnace are up to the appropriate standard, casting. And the valve body for magnetic particle flaw detection, for high temperature and high pressure valves are X-ray flaw detection.
After the casting is completed, the casting is subjected to the corresponding heat treatment, which mainly plays the role of refining the lattice and eliminating the internal stress. Gold processing before the casting shot blasting treatment (surface treatment) to improve the surface hardness and remove surface impurities. For stainless steel valves are pickled to remove the surface oxide layer.
Forging blanks are selected from the mechanical properties and chemical composition of qualified bars for forging. After forging, normalizing treatment; after gold processing according to the need for table machine processing, improve the corrosion resistance of forgings.
B. The sealing surface
Common sealing surface materials are divided into two categories: soft materials and hard materials. Among them, hard sealing surface materials are mainly copper alloy (T), stainless steel (H), cemented carbide (Y), etc.
H-type sealing surface selected 507Mo and 577 two kinds of welding electrodes overlay welding. After the seal surface overlay welding is completed for post-weld heat treatment to eliminate internal stress and improve the surface hardness. Among them, 507Mo overlay metal hardness is higher (HRC35-40), for the valve valve (valve plate) sealing surface; 577 overlay metal hardness is slightly lower (HRC28-33), for the valve body seat sealing surface. The choice of two different hardness of the material overlay welding, the seal between the hardness difference, so that the two sealing surface to obtain a good fit and anti-sassafras performance.
Y-type sealing surface is selected D802 and D812 welding electrode overlay welding. Seal surface after the completion of the weld heat treatment to eliminate internal stress, improve the surface hardness. Among them, D812 weld metal hardness is higher (HRC46-50), for the valve (valve plate) sealing surface; D802 weld metal hardness is slightly lower (HRC40-45), for the valve body valve seat sealing surface. The choice of two different hardness of the material overlay welding, sealing the difference in hardness between the vice, so that the two sealing surface to obtain a good fit and anti-sassafras performance.
After the completion of gold processing, the next metal surface processing process is very important, that is, surface grinding, surface roughness of Ra0.4 or less, flatness to 0.03 or less, so that the valve to obtain a good sealing performance. Using Will’s metal surface processing equipment, the sealing surface can be perfectly solved to obtain a surface roughness of 0.02 or so and greatly provide the hardness, wear and corrosion resistant valve workpiece.
For stainless steel valve sealing surface is often the body processing, that is, the sealing surface directly on the valve body or valve flap processing. According to user needs can also be overlay welding STL alloy.
Seal surface gold processing is completed after the penetration flaw detection to ensure reliable sealing.
C. The valve stem
The valve body material is carbon steel, the stem material is Cr13 or 18-8Cr series stainless steel. For the Cr13 material stem in the gold processing before the tempering treatment (quenching + high-temperature tempering), after heat treatment, its hardness reaches HB240-280. valve stem by tempering treatment, can obtain good overall mechanical properties. Thus improving the performance of the valve.
For 18-8Cr series stainless steel valve stem, the surface hardening treatment (nitriding treatment, etc.). To improve the corrosion resistance and anti-scuffing of the valve stem.
The difference between forged and cast valves
Casting is a material cast in the mold as a whole, it has a uniform distribution of stress, and there is no restriction on the direction of pressure. Forgings are pressed by the same direction of force, its internal stress is directional, and can only withstand directional pressure.
The same material, the same wall thickness of the casting and forgings, in strength and crystal phase structure, forgings are better than castings.
For the valve, the same poundage, the same material castings valve wall thickness to thicker than forgings. Its pressure strength is equal to that of forgings.
Castings are more demanding for the casting process, the biggest feature is that they can make more complex shapes, the valve body structure as well as the flow channel are irregular, casting can be formed at once, as long as the process is satisfactory, you can cast the body of the valve with a large diameter.
The denseness of forgings is better, but for too complex flow paths and shapes can not be formed at once, often need to be modular, forged separately and then welded together, so the size of forgings is somewhat limited. Forgings are often not machined to produce complex, streamlined runners. The runners are machined by turning, forming many sharp corners inside the transition, which can easily cause uneven stress and cracking at these sharp corners. At the same time, the modular welded design, forged valve seat diameter is relatively fixed, in some valve sizes, its diameter is small, affecting the flow capacity. Causes the valve flow resistance to increase, the whole system efficiency is reduced. Due to the limitations of the forging process in large size valves, and to save costs, many manufacturers usually use the center part of the valve body castings, forgings at both ends of the structure. Whether castings, forgings. In processing, there are possible product defects.
Castings of the main defects in the trachoma, bubbles, etc.; forgings of the main defects in the large grain, cold hard phenomenon, cracks, cracks, etc..
In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, while using X-ray, magnetic particle flaw detection, penetration inspection and other detection means. For forgings, this requires a strict heat treatment of the weld and corresponding inspection means to ensure. Forgings often require ultrasonic inspection. In addition, it should be mentioned that the welding process is very strict, and the qualification of welding engineers is also the key to ensure product quality.
Forging and casting are two different processes, which are briefly summarized above as follows:
Casting: The molten liquid metal fills the cavity and cools. The middle of the manufactured part is prone to air holes.
Casting: the metal is heated and melted and poured into the sand or mold, and then cooled and solidified into an object. The difference of performance forging, metal through plastic deformation, there is a refinement of the grain, cutting fiber continuous, so often used in important parts of the gross Pi manufacturing, such as shafts, tooth theory, etc..
Forging: Mainly extrusion method at high temperature. It can refine the grains in the parts.
Forging: Using hammering and other methods, the metal material in the plastic state becomes a workpiece with a certain shape and size, and changes its physical properties.
Uses of valves
Specifically, valves have the following uses:
- To connect or cut off the medium in the pipeline. Such as gate valve, globe valve, ball valve, plug valve, diaphragm valve, butterfly valve, etc.
- Regulation, control the flow and pressure of the medium in the pipeline. Such as throttle valve, regulating valve, pressure reducing valve, safety valve, etc.
- Change the direction of media flow in the pipeline. Such as distribution valve, three-way plug, three-way or four-way ball valve, etc.
- Stop the backflow of media in the pipeline. Such as a variety of different structures of the check valve, bottom valve, etc.
- Separate media. Such as steam traps and air traps of various configurations.
- Indicate and adjust the liquid level. Such as liquid level indicator, liquid level regulator, etc.
- Other special applications. Such as temperature control valves, emergency shut-off valves for overflow protection, etc.
Among the various general-purpose valves mentioned above, the number of valves used to connect and cut off the flow of media in the pipeline accounts for about 80% of the total number of valves.
How to choose the right valve?
To select a valve, first grasp the performance and flow characteristics of the medium, as well as the performance of temperature, pressure, flow rate, and flow rate, and then, in combination with process, operation, and safety factors, select valves of the corresponding type, structure, and model specification . The selection of valves can refer to Table 2-1.
Table 2-1 Selection of valves
|Flow rate adjustment form||Medium|
|Particle free||With suspended particles||Viscous||Slippery|
|Angle||Available||Available||Available||Special use||Also use|
|Oblique intercept||Available||Available||Available||Special use|
|Parallel gate shape||Ordinary||Available||Available|
|With grooved gate||Available||Available||Available||Available|
|Wedge type||Available||special use||Available||Available||Available|
|Wedge gate shape||Grooved bottom||Available||Available|
|Bottom without groove||Available||Appropriately Available||Available||Available|
|Eccentric cock||Available||Appropriately Available||Available||Available||Available|
|Straight through||Available||Appropriately Available||Available||Available||Available||available|
Select the valve according to the flow characteristics
The shape of the opening and closing parts of the valve and the flow channel of the valve make the valve have certain flow characteristics. This must be taken into account when selecting a valve.
1. Valves for cutting off and connecting media
usually choose valves with small flow resistance and straight-through flow channels. Such valves include gate valves, globe valves, and plunger valves. The downward closed valve is rarely used because the flow path is tortuous and the flow resistance is higher than other valves. However, closed valves can also be used where higher flow resistance is allowed.
2. Valves for flow control Usually choose valves
that are easy to adjust flow . Such as regulating valves, throttle valves, and plunger valves, because the size of its valve seat is proportional to the stroke of the opening and closing parts. Rotary (eg, plug, ball, butterfly) and flexing body (pinch, diaphragm) valves can also be used for throttling control, but usually only within a limited range of valve sizes. In most cases, people usually change the shape of the valve disc of the globe valve for throttling. It should be pointed out that it is extremely unreasonable to change the opening height of the gate valve or globe valve to achieve the throttling effect. Because the flow rate of the medium in the pipeline is very high under the throttling state, the sealing surface is easily washed and worn, and the cutting and sealing effect is lost. Similarly, it is unreasonable to use a throttle valve as a cutting device. 3. Valves for reversing and diverting According to the needs of reversing and diverting, this valve can have three or more channels, and is suitable for choosing plug valves and ball valves. Most of the valves for reversing and shunting use this type of valve. In some cases, other types of valves, with two or more properly connected to each other, can also be used for reversing and diverting media. 4. Valves for medium with suspended particles If the medium contains suspended particles, it is suitable to use a valve whose opening and closing parts slide along the sealing surface with wiping effect. Such as flat gate valve.
Select the valve according to the connection form
There are many forms of connection between valves and pipelines, among which the most important are threaded, flanged and welded connections.
1. Threaded connection
This kind of connection is usually processed into tapered pipe or straight pipe thread at the inlet and outlet ends of the valve, so that it can be screwed into the threaded joint or pipe of the tapered pipe. Since this type of connection may present large leakage channels, these channels can be plugged with sealant, sealing tape or filler. If the material of the valve body is weldable, sealing welding can also be performed after threaded connection. If the material of the connecting parts is allowed to be welded, but the expansion coefficient is very different, or the working temperature changes greatly, the threaded connection must only be sealed and welded. The valves with threaded connection are mainly valves with a nominal diameter below 50mm. If the bore size is too large, the installation and sealing of the connection will be very difficult.
In order to facilitate the installation and removal of threaded valves, pipe joints can be used at appropriate positions in the piping system. Valves with a nominal diameter below 50mm can use pipe socket joints as pipe joints, and the threads of the pipe socket joints connect the two connected parts together.
2. Flange connection
Valves with flange connection are more convenient to install and disassemble, but they are more bulky than thread connection, and the corresponding price is also higher. Therefore, it can be applied to pipe connections of various diameters and pressures. However, when the temperature exceeds 350°C, due to the creep and relaxation of the bolts, gaskets and flanges, the load on the bolts will be significantly reduced, and leakage may occur in the heavily stressed flange connection.
3. Welding connection
This connection is suitable for various pressures and temperatures, and it is more reliable than flange connection when used under harsh conditions. However, it is difficult to disassemble and reinstall the valve connected by welding, so its use is limited to the occasions that can usually operate reliably for a long time, or use harsh conditions and high temperature. For example, on the pipelines of thermal power stations, nuclear power projects, and ethylene projects.
Welded valves with nominal diameters below 50mm usually have welded sockets to accept pipes with flat ends. Since the socket welding forms a gap between the socket and the pipe, the gap may be corroded by some medium, and the vibration of the pipe will fatigue the connection part, so the use of socket welding is limited to a certain extent.
In the occasions where the nominal conditions are large, the service conditions are harsh, and the temperature is high, the valve body is often connected by groove butt welding, and at the same time, there are strict requirements on the weld.
Select the valve according to the medium performance
Many media have a certain degree of corrosiveness; the same media, with the change of temperature, pressure and concentration, its corrosiveness is also different. Therefore, the valve suitable for the medium should be selected according to the corrosion resistance of the material.
1. Cast iron valves
(1) Gray cast iron valves
are suitable for water, steam, petroleum products, ammonia, and can work in most alcohols, aldehydes, ethers, ketones, fats and other less corrosive media. It is not suitable for hydrochloric acid, nitric acid and other media. But it can be used in concentrated sulfuric acid, because concentrated sulfuric acid can produce a passivation film on its metal surface. To prevent the corrosion of cast iron by concentrated sulfuric acid.
( 2) Ductile iron valves have strong
corrosion resistance and can work in a certain concentration of sulfuric acid, nitric acid, sulfuric acid, and acid salts. But it is not resistant to the corrosion of hydrofluoric acid, strong alkali, hydrochloric acid and ferric chloride hot solution. Avoid sudden heat and sudden cold during use, otherwise it will burst.
(3) Nickel cast iron valve
Alkali resistance is stronger than gray cast iron and nodular cast iron valves; nickel cast iron is an ideal valve material for dilute sulfuric acid, dilute hydrochloric acid and caustic alkali.
2. Carbon steel valves
The corrosion resistance of carbon steel valves is similar to that of gray cast iron, but slightly inferior to that of gray cast iron.
3. Stainless steel valves
Stainless steel valves have excellent atmospheric resistance, can resist nitric acid and other oxidizing media, and can also resist corrosion by alkali, water, salt, organic acids and other organic compounds. However, it is not resistant to the corrosion of non-oxidizing acids such as sulfuric acid and hydrochloric acid, nor is it resistant to dry hydrogen chloride, oxidizing chlorides, and organic acids such as oxalic acid and lactic acid.
Stainless steel containing 2% to 4% molybdenum, such as Cr18Ni12Mo2Ti, etc., has better corrosion resistance than chromium-nickel stainless steel, and its acid resistance in non-oxidizing acids and hot organic acids and chlorides is better than chromium-nickel stainless steel. The pitting resistance is also good.
Stainless steels containing titanium or niobium are more resistant to intergranular corrosion.
Stainless steel containing high chromium and high nickel has higher corrosion resistance than ordinary stainless steel, and can be used to treat sulfuric acid, sulfuric acid, mixed acid, sulfurous acid, organic acid, alkali, salt solution, hydrogen sulfide, etc., even at certain concentrations high temperature occasions. But it is not resistant to the corrosion of concentrated or hot hydrochloric acid, wet fluorine, chlorine, bromine, iodine, aqua regia, etc.
4. Copper valves
Copper valves have good corrosion resistance to water, sea water, various salt solutions, and organic matter. It has good corrosion resistance to sulfuric acid, phosphoric acid, acetic acid, dilute hydrochloric acid, etc. that do not contain oxygen or oxidants, and has good resistance to alkali. But it is not resistant to the corrosion of oxidizing acids such as nitric acid and concentrated sulfuric acid, nor the corrosion of molten metals, sulfur and sulfides. Avoid contact with ammonia, it can cause stress corrosion cracking of copper and copper alloys. When selecting, it should be noted that the grades of copper alloys are different, and their corrosion resistance has certain differences.
5. Aluminum valves
have good corrosion resistance to strong oxidizing concentrated nitric acid, and can resist organic acids and solvents. But it is not corrosion-resistant in reducing medium, strong acid and strong alkali. The higher the purity of aluminum, the better the corrosion resistance, but the strength decreases accordingly, so it can only be used as a valve or valve lining with very low pressure.
6. Titanium valve
Titanium is an active metal, which can form an oxide film with good corrosion resistance at room temperature. It is resistant to seawater, various chlorides and hypochlorites, wet chlorine, oxidizing acids, organic acids, alkalis, etc. But it is not resistant to the corrosion of relatively pure reducing acids, such as sulfuric acid and hydrochloric acid, and it is not resistant to the corrosion of nitric acid containing oxidants. Titanium valves have good resistance to pitting corrosion. However, stress corrosion will occur in red fuming nitric acid, chloride, methanol and other media.
7. Zirconium valve
Zirconium is also an active metal, it can form a tight oxide film, it has good corrosion resistance to nitric acid, chromic acid, lye, melt, salt solution, urea, sea water, etc., but not resistant to hydrogen fluorine acid, concentrated sulfuric acid, and aqua regia, and is also resistant to wet chlorine and oxidizing metal chlorides.
8. Ceramic valves Valves
made by melting and sintering mainly silicon dioxide, such as zirconia, alumina, silicon nitride, etc., have extremely high wear resistance and temperature resistance. In addition to heat insulation performance, it also has high corrosion resistance. In addition to being resistant to oxyfluoric acid, fluorosilicic acid and strong alkali, it can withstand heat-concentrated nitric acid, sulfuric acid, hydrochloric acid, aqua regia, salt solution and organic solvents. If other materials are used for this type of valve, the corrosion resistance of other materials should be considered when selecting.
9. Glass valves Valves
made by melting and sintering mainly silicon dioxide have the same corrosion resistance as ceramic valves.
10. Enamel valve
Mainly silicon dioxide is melted and fired on ferrous metal products, and its corrosion resistance is the same as that of ceramic valves.
11. FRP valve
The corrosion resistance of FRP varies with its adhesive. Epoxy FRP can be used in hydrochloric acid, phosphoric acid, dilute sulfuric acid and some organic acids; phenolic FRP has better corrosion resistance; furan FRP has better alkali resistance, acid resistance and comprehensive corrosion resistance.
12. Plastic valves
Plastic has certain corrosion resistance, and its corrosion resistance varies greatly with different types of plastics.
Also known as polyamide, it is a thermoplastic with good corrosion resistance. It can resist the corrosion of dilute acid, salt and alkali. It has good corrosion resistance to hydrocarbons, ketones, ethers, fats and oils. But it is not resistant to strong acid, oxidizing acid, phenol and formic acid.
⑵ Polyvinyl chloride Polyvinyl
chloride is a thermoplastic with good corrosion resistance. Ability to acid, alkali, salt, organic matter. Not resistant to the corrosion of concentrated nitric acid, oleum, acetic anhydride, ketones, halogenated, aromatics, etc.
Polyethylene has excellent corrosion resistance. It has good corrosion resistance to non-oxidizing acids such as hydrochloric acid, dilute sulfuric acid, and hydrofluoric acid, as well as dilute nitric acid, alkali, salt solution, and organic solvents at room temperature. But it is not resistant to the corrosion of concentrated nitric acid, concentrated sulfuric acid and other strong oxidants.
Polypropylene is a thermoplastic, and its corrosion resistance is similar to that of polyethylene, slightly better than polyethylene. It is resistant to most organic acids, inorganic acids, alkalis, and salts. However, it has poor corrosion resistance to strong oxidizing acids such as concentrated nitric acid, oleum, and chlorosulfonic acid.
(5) Phenolic plastics
can resist the corrosion of hydrochloric acid, dilute sulfuric acid, phosphoric acid and other non-oxidizing acids and salt solutions. However, it is not resistant to strong oxidizing acids such as nitric acid and chromic acid, alkalis and some organic solvents.
(6) Chlorinated polyether,
also known as polychlorinated ether, is a linear thermoplastic with high crystallinity. It has excellent corrosion resistance, second only to fluoroplastics. It can resist the corrosion of various acids, alkalis, salts and most organic solvents except concentrated sulfuric acid and concentrated nitric acid, but it is not resistant to the corrosion of liquid chlorine, fluorine and bromine.
(7) Chlorotrifluoroethylene Like other fluoroplastics, it has excellent corrosion resistance and other properties, and its corrosion resistance is slightly lower than that of polytetrafluoroethylene. It has good corrosion resistance to organic acids, inorganic acids, alkalis, salts, and various organic solvents. Some solvents containing halogen and oxygen at high temperature can make it swell. It is not resistant to high temperature fluorine, fluoride, molten alkali, concentrated nitric acid, aromatic hydrocarbons, fuming nitric acid, molten alkali metal, etc.
PTFE has very excellent corrosion resistance, except for molten metal lithium, potassium, sodium, chlorine trifluoride, oxygen trifluoride at high temperature, and liquid oxygen at high flow rate, it can withstand almost all Corrosion of chemical media.
(9) Plastic-lined valves
Due to the low strength of plastics, many valves use metal linings as the outer shell and plastics as the lining. Plastic lined valves, with different lining plastics, have different corrosion resistance. The corrosion resistance of the plastic lining is the same as the corresponding plastic in the above plastic valve. However, when selecting, the corrosion resistance of other materials used in plastic-lined valves should be considered.
(10) Rubber-lined valve The
rubber is soft, so many valves are lined with rubber to improve the corrosion resistance and sealing performance of the valve. With the different types of rubber, its corrosion resistance varies greatly. Vulcanized natural rubber is resistant to non-oxidizing acids, alkalis, and salts, but not to strong oxidants, such as nitric acid, chromic acid, concentrated sulfuric acid, or to petroleum products and some organic solvents. Therefore, natural rubber is gradually replaced by synthetic rubber. Nitrile rubber in synthetic rubber has good oil resistance, but it is not resistant to corrosion by strong solvents such as oxidizing acids, aromatic hydrocarbons, fats, ketones, ethers; fluororubber has excellent corrosion resistance and can withstand various acids, alkalis, salts, petroleum products, Hydrocarbons, etc., but the solvent resistance is not as good as fluoroplastics; polyether rubber can be used in water, oil, ammonia, alkali and other media.
(11) Lead-lined valves
Lead is an active metal, but because of its soft material, it is often used as a lining for special valves. The corrosion product film of lead is a strong protective layer. It is a well-known material resistant to sulfuric acid. It has high corrosion resistance in phosphoric acid, chromic acid, carbonic acid, neutral solution, seawater and other media, but it is not resistant to alkali and hydrochloric acid. corrosion and are not suitable for working in their corrosion products.
Select valves according to temperature and pressure
In addition to the selection of valves to consider the corrosive properties of the medium, flow characteristics, connection form, the temperature and pressure of the medium is an important parameter.
1. The use of the valve temperature
The use temperature of the valve is determined by the material used to manufacture the valve. The use temperature of commonly used materials for valves is as follows:
- Gray cast iron valves using temperature of -15-250 ℃.
- Malleable cast iron valves using temperature of -15-250 ℃.
- Ductile iron valves use a temperature of -30-350°C.
- High nickel cast iron valves with a maximum operating temperature of 400°C
- carbon steel valves using temperature of -29-450 ℃, in JB/T3595-93 standard recommended use temperature t < 425 ℃.
- 1Cr5Mo, alloy steel valves maximum use temperature of 550 ° C.
- 12Cr1MoVA, alloy steel valve maximum use temperature of 570 ℃.
- 1Cr18Ni9Ti, 1Cr18Ni12Mo2Ti stainless steel valves using temperature of -196-600 ℃.
- Copper alloy valves using temperature of -273-250 ° C.
Plastic valves maximum use temperature.
- 100°C for nylon.
- 100°C for chlorinated polyether.
- 60°C for polyvinyl chloride.
- Polytrifluoroethylene -60-120℃.
- Polytetrafluoroethylene -180-150°C.
- Rubber diaphragm valves, the use of which varies in temperature depending on the type of rubber.
- 60°C for natural rubber.
- Nitrile rubber, neoprene for 80 ° C.
- 200°C for fluorine rubber.
- Valve lining with rubber, plastic, the temperature resistance of rubber, plastic performance shall prevail.
Ceramic valves, because of its poor temperature resistance to rapid change, generally used in the working conditions below 150 ℃. Recently, there is a super performance ceramic valve, can withstand temperatures below 1000 ℃.
Glass valves, poor in temperature resistance, are generally used for working conditions below 90℃.
Enamel valve, temperature performance is limited by the seal material, the highest use temperature does not exceed 150 ℃.
2. Pressure of the valve
The pressure of the valve is determined by the material used to manufacture the valve.
- Gray cast iron valves allow the use of the maximum nominal pressure of 1MPa.
- The maximum nominal pressure allowed for malleable cast iron valves is 2.5MPa.
- Ductile iron valves are allowed to use a maximum nominal pressure of 4.0MPa.
- Copper alloy valves are allowed to use a maximum nominal pressure of 2.5MPa.
- Titanium alloy valves are allowed to use a maximum nominal pressure of 2.5MPa.
- Maximum allowable nominal pressure for carbon steel valves is 32MPa.
- Maximum allowable nominal pressure for alloy steel valves is 300MPa.
- Stainless steel valves are allowed to use a maximum nominal pressure of 32MPa.
- Plastic valves are allowed to use a maximum nominal pressure of 0.6MPa.
- Ceramic, glass, enamel valves allowed to use a maximum nominal pressure of 0.6MPa.
- Glass steel valves allow the use of the maximum nominal pressure of 1.6MPa.
3. The relationship between valve temperature and pressure
Valve temperature and pressure have a certain intrinsic relationship, but also affect each other. Among them, the temperature is the dominant factor, certain pressure of the valve is only adapted to a certain temperature range, the valve temperature changes can affect the valve pressure.
For example: a carbon steel valve nominal pressure of 10MPa, when the medium working temperature of 200 ℃, its maximum working pressure P20 for 10MPa; when the medium working temperature of 400 ℃, its maximum working pressure P40 for 5.4MP; when the medium working temperature of 450 ℃, its maximum working pressure P54 for 4.5MPa.
Determine the diameter of the valve according to the flow rate and flow rate
The flow rate and flow rate of the valve mainly depend on the diameter of the valve, and are also related to the resistance of the structure of the valve to the medium. At the same time, there is a certain internal relationship with the pressure, temperature and concentration of the medium and other factors of the valve.
The flow channel area of the valve is directly related to the flow rate and flow rate, and the flow rate and flow rate are two interdependent quantities. When the flow rate is constant, the larger the flow rate, the smaller the flow channel area; the smaller the flow rate, the larger the flow channel area. Conversely, the larger the flow channel area, the smaller the flow rate; the smaller the flow channel area, the higher the flow rate. The flow rate of the medium is high, and the diameter of the valve can be smaller, but the loss of resistance is relatively large, and the valve is easily damaged. If the flow rate is large, it will produce electrostatic effects on flammable and explosive media, causing danger; if the flow rate is too small, the efficiency will be low and uneconomical. For viscous and explosive media, a smaller flow rate should be used. For oil and liquid with high viscosity, the flow rate is selected according to the viscosity, generally 0.1-2m/s.
Typically, the flow rate is known and the flow rate can be determined empirically. See Table 2-2 for common flow rates of various media. The nominal diameter of the valve can be calculated from the flow rate and flow rate.
The valve diameter is the same, its structure type is different, and the fluid resistance is also different. Under the same conditions, the greater the resistance coefficient of the valve, the more the flow rate and flow rate of the fluid passing through the valve will decrease; the smaller the resistance coefficient of the valve, the less the flow rate and flow rate of the fluid passing through the valve will decrease. The flow rates of common media are shown in Table 2-2.
Table 2-2 Flow rate tables commonly used for various media
|Liquid name||Conditions of Use||
|Liquid name||Conditions of Use||Velocity (m/s)|
ρ<0.01 (gauge pressure)
ρ<0.15 (gauge pressure)
ρ<2.5 (gauge pressure)
|Low pressure steam||ρ<1.0 (absolute pressure)||15-20|
|Medium pressure steam||Ρ=1.0-4.0 (absolute pressure)||20-40||Liquid ammonia||
Ρ≤0.6 (gauge pressure)
Ρ≤2.0 (gauge pressure)
|High pressure steam||Ρ=4.0-12.0 (absolute pressure)||40-60|
Ρ≤0.3 (gauge pressure)
Ρ=0.3-0.6 (gauge pressure)
Ρ=0.6-1.0 (gauge pressure)
Ρ=1.0-2.0 (gauge pressure)
Ρ=2.0-3.0 (gauge pressure)
Ρ=3.0-30.0 ( Gauge)
Ρ=0-0.05 (gauge pressure)
Ρ=0.05-0.6 (gauge pressure)
Ρ=0.6-1.0 (gauge pressure)
Ρ=1.0-2.0 (gauge pressure)
Ρ=2.0-3.0 (gauge pressure)
|Water and liquids of similar viscosity||
Ρ=0.1-0.3 (gauge pressure)
Ρ≤1.0 (gauge pressure ) Ρ≤8.0 (gauge pressure
Ρ≤20-30 (gauge pressure)
heating network circulating water, cooling water
pressure return water
no pressure return water
|Semi water gas||Ρ=0.1-0.15 (gauge pressure)||10-15|
|Natural gas||30||Tap water||
Main pipe Ρ=0.3 (gauge pressure)
branch pipe Ρ=0.3 (gauge pressure)
|Nitrogen||Ρ=5-10 (absolute pressure)||15-25|
Ρ<0.3 (gauge pressure)
Ρ<0.6 (gauge pressure)
Ρ≤2 (gauge pressure)
|Boiler feed water||>3|
|Sea water, slightly alkaline water||Ρ<0.6 (gauge pressure)||1.5-2.5|
Note: The unit of DN value is: mm; the unit of Ρ value is: MPa.
The resistance coefficient of the gate valve is small, only in the range of 0.1 to 1.5; the resistance coefficient of the gate valve with a large diameter is 0.2 to 0.5; the resistance coefficient of the shrink gate valve is larger. The resistance coefficient of the globe valve is much larger than that of the gate valve, generally between 4 and 7. The Y-type globe valve (straight-flow type) has the smallest resistance coefficient, which is between 1.5 and 2. The resistance coefficient of forged steel globe valve is the largest, even as high as 8.
The resistance coefficient of the check valve depends on the structure: the swing check valve is usually about 0.8 to 2, and the resistance coefficient of the multi-disc swing check valve is relatively large; the resistance coefficient of the lift check valve is the largest, up to 12. .
The resistance coefficient of the plug valve is small, usually about 0.4 to 1.2.
The resistance coefficient of the diaphragm valve is generally around 2.3.
The resistance coefficient of the butterfly valve is small, generally within 0.5.
The resistance coefficient of the ball valve is the smallest, generally around 0.1.
The resistance coefficients of the above valves are values when the valve is fully open.
The selection of the valve diameter should take into account the processing accuracy and size deviation of the valve, as well as other factors. There should be a certain margin in the diameter of the valve, generally 15%. In actual work, the diameter of the valve depends on the diameter of the process pipeline.
Comprehensively determine the structure type of the valve according to the working conditions and process operation
1. Process requirements
Ammonia has a corrosive effect on copper, so valves made of copper cannot be used. In the process flow containing ammonia in the medium, the structure of the stop valve is different from that of the general valve, and its sealing surface is made of Babbitt alloy.
Non-directional valves should be used for pipelines with two directions of flow. In an oil refinery, after the heavy oil pipeline stops running, it is necessary to use steam to reversely purge the pipeline to prevent the heavy oil from solidifying and blocking the pipeline, so it is not suitable to use a stop valve. Because when the medium flows in reverse, it is easy to erode the sealing surface of the stop valve, so it is better to choose a gate valve.
For some media with crystallization or sedimentation, globe valves and gate valves are not suitable, because their sealing surfaces are easily worn by crystallization and sedimentation. Therefore, it is more appropriate to choose a ball valve or a plug valve; a flat gate valve is also an option, but it is best to use a pinch valve.
In the selection of gate valves, the bright rod single gate is more suitable for corrosive media than the dark rod double gate; the single gate is suitable for medium with high viscosity; the wedge double gate is more adaptable to high temperature and sealing surface deformation than the wedge The type single gate is better, and there will be no jamming phenomenon due to temperature changes, especially superior to the single gate without elasticity.
When it is necessary to accurately adjust the small flow rate, it is not appropriate to need a stop valve, and a needle valve or a throttle valve should be used. When it is necessary to keep the pressure after the valve stable, a pressure reducing valve should be used.
For high-pressure and ultra-high-pressure media, right-angle globe valves are often used, because right-angle globe valves are usually made of forged steel, and the pressure resistance of forged steel is relatively stronger than that of cast steel.
2. Economic rationality
For corrosive media, if the temperature and pressure are not high, non-metallic valves should be used as much as possible; if the temperature and pressure are high, lining valves can be used to save precious metals. When choosing non-metallic valves, economic rationality should still be considered. For example, polytetrafluoroethylene is not used when polyvinyl chloride can be used, because polytetrafluoroethylene is more expensive than polyvinyl chloride.
For occasions with high temperature and high pressure, the temperature and pressure gauge should be used. If ordinary carbon steel valves can meet the requirements of use, alloy steel valves should not be used, because the price of alloy steel valves is much higher.
For medium with high viscosity, small flow resistance is required, and valves with small flow resistance such as Y-type DC globe valve, gate valve, ball valve, and plug valve should be used. The valve with small flow resistance consumes less energy.
For low-pressure, high-flow water, air and other media, it is more reasonable to choose large-diameter gate valves and butterfly valves. Butterfly valves can be used for cut-off and throttling.
3. Safety and reliability
Generally, ductile iron valves and cast steel valves can be used on steam pipelines. But on the outdoor steam pipeline, if the gas supply is stopped, the water will freeze easily and the valve will break, especially in northern my country. Therefore, it is advisable to use cast steel or forged steel valves, and at the same time, it is necessary to do a good job of antifreeze and heat preservation for the valves.
Acetylene is a flammable and explosive medium, which requires high sealing performance. When the pressure is below 0.6MPa, a diaphragm valve should be used, but it should not be used on the pipeline of vacuum equipment. For highly harmful radioactive media and highly toxic media, valves with bellows structure should be used to prevent the media from leaking from the stuffing box.
For valves with driving devices (electric, hydraulic, pneumatic), in addition to requiring safe and reliable driving devices, corresponding driving devices should be selected according to different working conditions. For example, in the working condition where fire protection is required, valves with hydraulic and pneumatic devices should be used; when valves with electric devices must be used, the electric devices should be explosion-proof to avoid fires caused by arcs.
4. Convenient operation and maintenance.
For large valves and valves at high altitude, high temperature, high pressure, danger and long distance, gear transmission, chain transmission or valves with electric, pneumatic and hydraulic devices should be selected.
In the occasion where the operating space is limited, it is not suitable to use a rising stem gate valve, and it is better to choose a dark stem gate valve. It is best to use a butterfly valve.
For valves that require quick closing and quick opening, it is not suitable for general gate valves and globe valves. Ball valves, plug valves, butterfly valves, quick opening gate valves, etc. should be required according to other requirements.
Gate valves and globe valves are the two most widely used types of valves. When choosing, it should be considered comprehensively. The gate valve has small flow resistance and less energy consumption for transporting the medium, but it is difficult to maintain; the stop valve has a simple junction and is easy to maintain, but the flow resistance is relatively large. From the perspective of maintenance, the maintenance of globe valves is more convenient than that of gate valves; the pressure drop of water and steam in globe valves is not large, so globe valves are widely used in medium pipelines such as water and steam. However, in mediums with high viscosity such as petroleum products, although gate valves are difficult to maintain, they are still widely used. In the pipeline with welded connection, the stop valve with welded connection should be selected as much as possible, and the gate valve with welded connection should not be selected. Because repairing the sealing surface of the gate valve on the pipeline is much more difficult than repairing the sealing surface of the globe valve, and the gate valve and the valve seat are easily stuck when the temperature changes greatly.
Selection of driving valve
Valves such as gate valves, globe valves, ball valves, butterfly valves, plug valves, throttle valves, and diaphragm valves are widely used as pipeline closing devices, among which gate valves and globe valves are the most used.
Section 6 of the first chapter systematically describes the terminology, structural form, scope of application, etc. of the valve, which can be used as the basis for the selection of the valve category and model. After the category and model of the valve are determined, the shell material, sealing surface material, applicable temperature, applicable medium, nominal diameter, etc. of the valve are determined accordingly. Depending on the circumstances, the following steps can be followed.
1. Valve selection steps (
(1) According to the medium characteristics, working pressure and temperature, compare the data provided in the second paragraph of “selecting valves according to medium performance” and “selecting valves according to temperature and pressure” in this section and Table 2-3a, Table 2-3b Select valve body material, sealing surface material.
(2) According to the material of the valve body, the working pressure and temperature of the medium, determine the nominal pressure level of the valve according to Table 1-3, Table 1-4, and Table 1-5.
(3) Select the sealing surface material according to the nominal pressure, medium characteristics and temperature. Make its maximum operating temperature not lower than the working temperature of the medium.
(4) Determine the nominal diameter according to the calculated value of the pipe diameter. In general, the nominal diameter of the valve adopts the diameter of the pipe.
(5) Select the driving mode of the valve according to the purpose of the valve and the requirements of the production process conditions.
(6) Select the connection form of the valve according to the connection method of the pipeline and the nominal diameter of the valve.
(4)Select the type, structure and model of the valve according to the nominal pressure, medium characteristics, working temperature and nominal diameter of the valve.
Table 2-3a Selection list of commonly used valve body materials
|Material||Common working conditions||Main medium|
|Category||Material grade||Code name||PN/MPa||t/℃|
|Grey cast iron||HT200||Z||≤1.6||≤200||Water, steam, oil, etc.|
|Malleable cast iron||KT30-6||K||≤2.5||
ammonia ≥ -40
|High silicon cast iron||NSTSi-1S||G||≤0.6||≤120||Nitric acid and other corrosive media|
|High quality carbon steel||ZG200, ZG250, WCB||C||≤16||≤450||
Water, steam, oil, etc.
Ammonia , nitrogen, hydrogen, etc.
|A3, 10, 20, 25, 35||≤32||≤200|
|Chromium Molybdenum Alloy Steel||
12CrMo, WC6, 15CrMo
|Chromium molybdenum vanadium alloy steel||
ZG12Cr1MoV, ZG15Cr1MoV, WC9
Nickel, chromium, titanium,
|Nitric acid and other corrosive media|
|Low temperature media such as ethylene|
|High temperature steam, gas, etc.|
|R||≤20||≤200||Urea, acetic acid, etc.|
|High quality manganese vanadium steel||
|I||≤16||≤450||Water, steam, oil, etc.|
|copper alloy||HSi80-3||T||≤4.0||≤250||Water, steam, gas, etc.|
Table 2-3b Selection list of commonly used sealing surface materials
|Material||Code name||Common working conditions||Applicable valve|
|Tubber||x||≤0.1||≤60||Globe valve, diaphragm valve, butterfly valve, check valve, etc.|
|Nylon||N||≤32||≤80||Ball valve, globe valve, etc.|
|PTFE plastic||f||≤6.4||≤150||Ball valve, globe valve, plug valve, gate valve, etc.|
|Babbitt||B||≤2.5||—70-150||Ammonia globe valve|
|T||≤1.6||≤200||Gate valve, globe valve, check valve, plug valve, etc.|
, 3Cr13 TDCr-2
|h||≤3.2||≤450||Medium and high pressure valves|
|Nitriding steel 38CrMoALA||D.||P5410||540||Power station gate valve, generally not used|
|Carbide||WC, TiC||Y||Determined by valve body material||High temperature valve, ultra high pressure valve|
|Determined by valve body material||
High pressure, ultra high pressure valve
High temperature , low temperature valve
|Processing on the body||Cast iron||W||≤1.6||≤100||Gas and oil gate valves, globe valves, etc.|
|High quality carbon steel||≤4||≤200||Oil valve|
|≤32||≤450||Valves for corrosive media such as acids|
2. Examples of driving valve selection
[Example 1] The working pressure of the steam pipeline is 1.3MPa, the temperature is 350°C, and the nominal diameter is 100mm. Try to choose a closed-circuit valve.
【Solution】Valve body material: It is known that the steam pressure is 1.3MPa and the temperature is 350°C. The valve body material can be selected from ductile iron or high-quality carbon steel according to Table 2-3a. However, considering that 350°C has reached the maximum service temperature of ductile iron, for safe use, high-quality carbon steel (WCB, ZG230-450) valves should be selected.
Nominal pressure: According to the pressure and temperature of high-quality carbon steel and steam, it is found out from Table 1-3 that the nominal pressure of the valve is PN=2.5MPa.
Sealing surface material: According to the nominal pressure of the valve and medium temperature, the sealing surface material should be stainless steel according to Table 2-3b.
Drive mode: According to the given nominal diameter DN100mm, because the pipe diameter is small, the torque required for opening and closing is not large. This example does not put forward special requirements for the operation mode, so the handwheel drive is selected.
Connection form: According to the given steam pressure and temperature, the pipe material should be seamless steel pipe, and the seamless steel pipe should be welded. However, in order to facilitate the loading, unloading and maintenance of the valve, its connection form should not be welded, but flanged connection should be used.
Valve category and model: According to medium characteristics, nominal pressure and nominal diameter, globe valve or gate valve can be selected. Because the price of the gate valve is higher than that of the globe valve under the same pressure level, the globe valve should be preferred. However, in the globe valve parameter table, there is no carbon steel product with a nominal pressure of PN2.5MPa, so the gate valve is still used in this example. Select the valve model Z40H-25 DN100 according to the gate valve parameter table.
[Example 2] For an oil pipeline, the working pressure of the medium is 11.5MPa, the temperature is 340°C, and the inner diameter of the pipeline is 107mm; try to select a suitable closed-circuit valve.
[Solution] Valve body material: According to the characteristics and parameters of the medium, high-quality carbon steel (WCB, ZG230-450) can be selected according to Table 2-3a.
Nominal pressure: According to high-quality carbon steel material and medium parameters, the nominal pressure of the valve is PN=16MPa.
Sealing surface material: According to the nominal pressure of the valve and the temperature of the medium, stainless steel or hard alloy steel can be selected according to Table 2-3b.
Driving mode: no special requirements are mentioned in this example, and handwheel driving can be used.
Connection form: flange connection.
Nominal diameter: According to the medium parameters, the pipe can be made of No. 50 high-quality carbon steel seamless steel pipe. According to the inner diameter of the pipe of 107mm, the nominal pressure of 11.5MPa and the allowable stress of No. 20 steel at a temperature of 340°C, the wall thickness of the pipe is selected as 14mm, the calculated outer diameter of the pipe is DW=107+2×14=135mm, the outer diameter is 140mm, and the nominal diameter is DN=125mm. The nominal diameter of the valve should be the same as the pipe.
Type and model of valves: gate valves should be used for oil pipelines. According to the parameters in the valve parameter table, when PN=16MPa, the maximum nominal diameter of the stop valve is 40mm, and the maximum nominal diameter of the gate valve under the same pressure level is 200mm, so the gate valve should also be selected. According to the gate valve parameter table, there are two types of carbon steel handwheel flange gate valves under PN16MPa: Z41H-160 and Z41Y-160. However, the maximum nominal diameter of the former is 40mm, while the maximum nominal diameter of the latter is 200mm, so the Z41Y-160 gate valve should be selected, and the valve sealing surface is made of hard alloy. The full name of the selected furan is: rising stem wedge single disc gate valve (Z41Y-160 DN125).
Automatic valve selection
The selection of automatic valves is the same as that of general valves. In addition to considering economical rationality and durability, automatic valves are also required to be sensitive, reliable, and accurate in adjustment.
1. Selection of check valve
The function of the check valve is to only allow the medium to flow in one direction and prevent the flow in the opposite direction. Commonly used check valves are divided into lift type and swing type.
On high-pressure and small-diameter equipment or pipelines, lift check valves are usually used. For pipelines that require a small pressure drop, lift check valves should not be used, because of their large flow resistance, butterfly check valves or swing check valves should be used. On pipelines with large pressure fluctuations and special requirements. In order to prevent the disc from being damaged due to water hammer, a swing check valve with a buffer device should be selected. When the caliber is large, a multi-flap swing check valve is used. At the outlet of the boiler feed water pump, a special empty check valve should be selected to prevent the medium from flowing back and improve the efficiency of the pump. The check valve used at the bottom of the pump suction pipe should be a bottom valve.
Ordinary swing check valves or lift check valves should try to avoid excessive caliber. In order to make the check valve flap fully open or open to the proper position with the minimum flow rate, in some applications, the diameter of the check valve must be smaller than the diameter of the corresponding pipe.
In order to meet the needs of various purposes, there are also many kinds of check valves, such as: ball check valves. Thread lift stop check valve, swing check valve without impact, oblique disc check valve, conical diaphragm check valve, etc.
According to the different media, the disc can be made of metal entirely, or inlaid with leather, rubber on the metal, or use synthetic coverage, thermal spraying and other alloy materials.
2. Selection of pressure reducing valve
The pressure reducing valve reduces the inlet pressure to a certain required outlet pressure through the throttling of the opening and closing parts, and can use its own medium energy to keep the outlet pressure basically constant when the inlet pressure and flow change. Changed valve.
The pressure reducing valve is divided into direct acting type and pilot operating type.
(1) Direct acting type
Direct-acting pressure reducing valves are loaded with a compression spring, weight or gravity lever, and compressed air. Valve with direct pressure control via diaphragm, piston or bellows. The valve structure is simple and durable. Under relatively harsh working conditions, as long as it is properly maintained, it can also have a long life. Although direct-acting pressure regulation is not as precise as pilot-operated, it is less expensive. It can be widely used in occasions where precise control is not necessary.
Commonly used direct-acting pressure reducing valves are divided into structural forms: spring diaphragm pressure reducing valve, piston type pressure reducing valve, bellows type pressure reducing valve and lever type pressure reducing valve. The spring diaphragm pressure reducing valve is a pressure reducing valve that uses a diaphragm as a sensitive element to drive the movement of the disc. It has high sensitivity and is suitable for water and air medium pipelines with low temperature and pressure.
The piston pressure reducing valve is a pressure reducing valve that uses a piston as a sensitive element to drive the movement of the disc. Due to the greater friction that the piston bears in the cylinder, the sensitivity is not as good as that of the thin-film pressure reducing valve. Therefore, it is suitable for pipelines and equipment with steam and air as the working medium that withstand high temperature and pressure.
The bellows type pressure reducing valve is a pressure reducing valve that uses the bellows as the sensitive element to drive the movement of the disc. It is suitable for pipelines of clean media such as steam and air with low media parameters. Not for decompression of liquids. It cannot be used on pipelines containing solid particle media. Therefore, it is advisable to add a filter before the bellows pressure reducing valve. When selecting a pressure reducing valve, care should be taken not to exceed the pressure reducing range of the pressure reducing valve. And ensure that it is used under reasonable circumstances.
The lever type pressure reducing valve is a pressure reducing valve that uses a weight or a gravity lever as a sensitive element to drive the movement of the disc. This form is structurally simple and durable, but imprecise. Currently less used.
(2) Pilot type
The pilot-operated pressure reducing valve is composed of a main valve and a pilot valve. The change of the outlet pressure is amplified by the pilot valve to control the action of the main valve. In this type of valve, the role of the pilot valve is to assist in controlling the main valve or to completely control the main valve. The pilot valve itself can be a small direct acting pressure reducing valve. The precise control of such a valve depends on its specific construction. And in essence. The purpose of the pilot valve is to adjust the opening amount of the main valve by maintaining the flow rate under the predetermined pressure. The pressure control accuracy of the pilot pressure reducing valve is very precise, and the structure is compact. For the pressure reducing valve with the same function, the pilot type is usually much smaller than the direct acting type. In this form, the pilot valve and the main valve can be integrated, or a separate device suitable for remote pressure signal control. It can also be used for remote switch control, that is, in a complete system controlled by the control center. parts. In addition, a device directly controlled by temperature can be obtained by installing an appropriate type of pilot valve. Due to the complex structure of the pilot-operated pressure reducing valve, frequent maintenance and clean working conditions are required. Clean working conditions often install a filter at the valve inlet. Commonly used pilot-operated pressure reducing valves are divided into structural forms: pilot piston pressure reducing valves, pilot bellows pressure reducing valves and pilot film pressure reducing valves.
(3) Several issues that should be paid attention to when selecting a pressure reducing valve The
pressure reducing valve has a wide range of applications, including steam, compression opening, industrial gas, water, oil and other liquid media. Therefore, in view of many possible structural changes, when choosing a pressure reducing valve, the most important thing is the exact performance of the valve. First, it should be fully tested to ensure a good use effect. During testing, the pressure reducing valve should meet the following performance requirements:
① Within a given range of spring pressure levels, the outlet pressure should be continuously adjustable between the maximum value and the minimum value, without jamming and abnormal vibration.
② For soft-sealed pressure reducing valves, there must be no leakage within the specified time; for metal-sealed pressure reducing valves. Its leakage should not be greater than 0.5% of the maximum flow.
③ When the outlet flow rate changes, the negative deviation of the outlet pressure: the direct acting type is not more than 20%; the pilot type is not more than 10%.
④ When the inlet pressure changes, the negative deviation value of the outlet pressure: the direct acting type is not more than 10%; the pilot type is not more than 5%.
For the unused pressure reducing valve, adjust the spring to make it in a free state. The inlet and outlet ports shall be closed with blanking caps.
For the name, type and technical parameters of commonly used pressure reducing valves, see the pressure reducing valve part and appendix in Chapter 1, Section 6.
See Table 2-4 for the nominal diameter and orifice area of commonly used pressure reducing valves.
Table 2-4 Pressure relief valve hole area
|Nominal diameter DN(mm)||25||32||40||50||65||80||100||125||150|
|Seat passage area f (cm2)||2.0||2.8||3.48||5.30||9.45||13.2||23.5||36.8||52.2|
The flow rate of the pressure reducing valve is related to the nature of the fluid and the pressure ratio. The smaller the pressure ratio, the greater the flow rate; but when the pressure ratio decreases to a certain value, the flow rate will no longer increase with the decrease of the pressure ratio.
The valve hole area listed in the product specification of the pressure reducing valve is the maximum cross-sectional area, while the flow channel area under working conditions is smaller than this value, and the selected valve hole area should be slightly larger than the technical valve hole area.
To select a pressure reducing valve under a certain working condition, you can also refer to product catalogs and instructions, and strive to be scientific and reasonable.
3. Selection of safety valve
Safety valve is an automatic valve, which uses the force of the medium itself to discharge a rated amount of fluid without any external force, so as to prevent the internal pressure of the system from exceeding the predetermined safety value. When the pressure returns to normal, the valve closes again and prevents the medium from continuing to flow out. Safety valves are used in boilers, pressure vessels and other pressurized equipment as a safety protection device against overpressure. For some important pressurized systems, it is sometimes necessary to set up two or more overpressure protection devices. In this case, the safety valve is often used as the last protection device, so its reliability is particularly important to the safety of equipment and personal safety. significance.
The technical development of safety valves has gone through a long process, from the small-displacement micro-opening type to the large-displacement full-opening type, from the heavy hammer type (static weight type) to the lever heavy hammer type, spring type, and direct valve type. After the acting type, there is the indirect acting leading type.
Commonly used safety valves include direct-load safety valves, safety valves with power auxiliary devices, safety valves with supplementary loads, and pilot-operated safety valves according to their structural forms.
In modern industry, due to the limited load size, sensitivity to vibration and low return pressure of the hammer type safety valve and lever weight type safety valve, their application range has become smaller and smaller. The spring direct load safety valve and the pilot safety valve have their own characteristics that cannot be replaced by each other, and both have been developed at the same time.
(1) Lever weight hammer type safety valve. Adjust the pressure by moving the hammer position or changing the weight of the hammer. This kind of safety valve can only be fixed on the equipment, and the weight of the weight itself generally does not exceed 60kg to avoid difficult operation. The lever weight safety valve made of cast iron is suitable for the working conditions of nominal pressure PN≤1.6MPa and medium temperature t≤200℃. The lever weight safety valve made of carbon steel is suitable for the working conditions of nominal pressure PN≤4.0MPa and medium temperature t≤450℃. The lever weight safety valve is mainly used for working media such as water and steam.
(2) Spring direct load type safety valve. It uses the force of the compression spring to balance the pressure of the disc and make it seal. The spring direct load safety valve has the advantages of simple structure, sensitive response and good reliability. However, due to the spring loading, the load size is limited, so it cannot be used in the occasions of high pressure and large diameter. In addition, when the protected system is operating normally, the specific pressure on the sealing surface of the safety valve closure is determined by the difference between the valve and the normal operating pressure of the system. Is a small value, so it is more difficult to achieve a good seal. This is especially true when the valve closing member is a metal sealing surface and when the valve set pressure is relatively close to the normal operating pressure of the system. At this time, in order to ensure the necessary sealing, it is often necessary to adopt a special structure and carry out extremely fine processing and assembly. There are two types of spring direct load safety valves: closed type and non-closed type. Generally, the flammable, explosive or toxic medium is closed. Steam or inert gas can be selected as non-closed type. Some spring direct load safety valves have wrenches and some don’t. The function of the wrench is to check the sensitivity of the disc.
(3) Pilot-operated safety valve. It is a safety valve that is driven or controlled by the medium discharged from the pilot valve. The pilot valve itself should be a direct load safety valve that meets the requirements of the standard. Since the main valve of the pilot safety valve is usually loaded by the pressure of the working medium, its load is not limited. Therefore, it can be used in high pressure and large diameter occasions. At the same time, because the main valve can be designed to rely on the pressure of the working medium to seal, or a much larger load can be applied to the disc of the direct load safety valve, so the sealing of the main valve can be easily guaranteed. In addition, the action of this type of safety valve can be less affected by changes in back pressure, but the reliability of the pilot-operated safety valve is related to both the main valve and the pilot valve, and the structure is relatively complicated. In order to improve reliability, the code often requires the use of Multiple pilot control lines. This increases the complexity of the entire protection system. Based on the above reasons, the pilot-operated safety valve and the spring direct-loaded safety valve are widely used in both the process industry and the electric power industry, and they develop separately and together constitute the mainstream of safety valve structure development.
(4) Selection requirements for safety valves. When selecting a safety valve, the nominal pressure of the safety valve is usually determined by the operating pressure, the operating temperature range of the safety valve is determined by the operating temperature, and the pressure adjustment range of the spring or lever is determined by the calculated constant pressure value of the safety valve, which is determined according to the medium used According to the material and structural form of the safety valve, the nozzle cross-sectional area or nozzle diameter of the safety valve is calculated according to the discharge of the safety valve, so as to select the type and number of safety valves.
The working pressure levels of spring direct load safety valves are shown in Table 2-5, and there are five working pressure levels. When selecting, in addition to indicating the product model, name, medium, and temperature, the pressure level of the spring should also be indicated.
Table 2-5 Working pressure level of spring safety valve
Nominal pressure PN
The inlet and outlet of the safety valve are located at the high pressure and low pressure sides respectively, so the connecting flanges also adopt different pressure levels accordingly, as shown in Table 2-6.
Table 2-6 Pressure class MPa of inlet and outlet flanges of safety valves
|Safety valve nominal pressure||1.0||1.6||4.0||10.0||16.0||32.0|
|Inlet flange pressure level||1.0||1.6||4.0||10.0||16.0||32.0|
|Outlet flange pressure level||1.0||1.6||1.6||4.0||6.4||16.0|
When the medium is discharged through the safety valve, its pressure decreases, its volume expands, and its flow rate increases, so the outlet diameter of the safety valve is larger than the inlet diameter. For the micro-opening safety valve, the outlet diameter can be equal to the inlet diameter, because it is often used in liquid media because of its small displacement. The full-lift safety valve has a large displacement and is mostly used for gas media, so its outlet diameter is generally one level larger than the nominal diameter. The inlet and outlet diameters are selected according to Table 2-7.
Table 2-7 Safety valve inlet and outlet diameter mm
|Exit path||Slight start||10||15||20||25||32||40||50||80|
According to the standard: the direct load safety valve made of carbon steel and alloy steel is suitable for the working conditions of PN≤32MPa and DN≤150mm. Mainly used in media such as water, steam, ammonia, petroleum and oil products. The safety valve made of carbon steel is used for medium temperature t≤450℃, and the safety valve made of alloy steel is used for medium temperature t≤600℃.
The safety valve should have sufficient sensitivity. When the opening pressure is reached, it should be opened without hindrance; when the discharge pressure is reached, the disc should be fully opened and reach the rated displacement; Close and keep airtight. The pressure of the safety valve shall meet the requirements in Table 2-8.
Table 2-8 Pressure specification MPa of safety valve
|Application area||Working pressure ρ||Opening pressure ρa||Reseat pressure ph||Discharge pressure ρv||Use|
ph -0.4 ph
For work For
When two safety valves are installed, one of them is a control safety valve; the other is a working safety valve. The opening pressure of the control safety valve should be slightly lower than the opening pressure of the working safety valve, so as to avoid the two safety valves opening at the same time and causing too much exhaust.
Due to the advancement of science and technology, some safety valves used in special environments and special working conditions continue to appear, such as safety valves on large thermal power stations, safety valves on petrochemical plants, and primary circuit devices on pressurized water reactors in nuclear power plants. safety valve etc. The safety valves on these devices ensure the normal operation and safety of the system. For details, see monographs on the subject.
4. Selection of steam trap
The steam trap is an automatic control device that automatically discharges condensed water from a closed container containing steam while keeping fresh steam from leaking. It also allows steam to pass through according to a predetermined flow rate when necessary. In modern society, steam is widely used in industrial and agricultural production and living facilities, whether in the steam pipeline system or using steam for heating, drying, heat preservation, disinfection, cooking, concentration, heat exchange, heating, air conditioning, etc. The condensed water generated during the process needs to be drained through the steam trap, and the steam is not allowed to leak out.
According to the driving mode of the opening and closing parts, steam traps can be divided into three categories: mechanical steam traps driven by condensate level changes; thermostatic steam traps driven by condensate temperature changes; Feature driven thermodynamic steam trap. See Table 1-25 for the structural type of the steam trap.
The steam trap is an important accessory of the steam utilization system, and its performance is crucial to the normal operation of the system. The improvement of equipment thermal efficiency and the rational use of energy play an important role.
(1) Mechanical steam traps
These traps mainly include closed float type, open upward float type, open downward float type and so on. The working principle of this type of steam trap uses the ancient Archimedes principle, which has reliable performance and can remove saturated water; but the volume is relatively large and cumbersome. And because the bumpy and swaying environment has a considerable impact on its steam resistance and drainage performance, it cannot be adapted to use on trains, ships and devices with relatively large vibrations.
(2) Thermostatic steam trap
Such traps mainly include steam pressure steam traps, bimetallic sheet or thermoelastic element steam traps, and liquid or solid expansion steam traps. This type of steam trap appeared almost at the same time as the mechanical type steam trap. At first, it was a metal expansion steam trap, which realized the effect of steam blocking and drainage by using the physical properties of the valve stem material’s cold shrinkage and thermal expansion and the change of condensate temperature. However, this type of steam trap cannot adapt to the situation where the steam pressure changes greatly and the amount of condensed water is unstable. Later, a pressure-balanced bellows steam trap using liquid expansion was developed. The above problems have been initially resolved. With the development of material science and technology, bimetallic strips have been widely used, and bimetallic strip steam traps have been developed, which use the deformation of bimetallic strips caused by temperature changes to realize the effect of steam blocking and drainage. This kind of trap is small in size, light in weight, and can remove a large amount of air, but it is expensive.
(3) Thermodynamic steam traps
This kind of traps include disc steam traps, pulse steam traps, fan-type steam traps, and orifice-plate steam traps. The disc steam trap uses the difference between the steam flow rate and the condensed water flow rate to realize the steam blocking and drainage action. This kind of steam trap is small in size, light in weight and simple in structure, but has poor air discharge performance. The pulse steam trap also has the characteristics of small size and light weight, but the structure is complicated, the manufacturing precision is high, and the price is expensive.
(4) Selection of steam traps
Since various types of steam traps have different advantages and disadvantages and different applicable conditions, various types of steam traps have coexisted for a long time for many years and are used in various industrial pipelines. Among many types of steam traps, it is necessary to correctly select the steam trap suitable for a certain system, because it has a great influence on the normal operation of the system, and proper selection can improve thermal efficiency and save fuel. The correct selection should be based on the following standards:
① The nominal pressure and operating temperature of the steam trap should be greater than or equal to the maximum operating pressure and operating temperature of the steam pipeline and steam-using equipment.
② Steam traps must be differentiated by type, and selected according to their working performance, conditions and condensate discharge, and the nominal diameter of the steam trap should not be used as the basis for selection.
③ In the condensed water recovery system, if the working back pressure is used to recover condensed water, a steam trap with a higher back pressure rate (such as a mechanical steam trap) should be selected.
④ When the steam used in the steam equipment must not accumulate condensed water, a steam trap that can continuously discharge saturated condensed water (such as a floating ball steam trap) should be selected.
⑤ In the condensed water recovery system, when the steam equipment uses steam to discharge saturated condensed water and steam to remove non-condensable gas in time, a steam trap capable of saturating water should be used in parallel with the exhaust device or a trap with both Steam traps with two functions of draining and exhausting (such as special manager type steam traps).
⑥ When the working pressure of steam-using equipment fluctuates frequently, a steam trap that does not need to adjust the working pressure should be selected.
⑦ Determination of the actual maximum working back pressure ρ′MOR of the steam trap.
Mechanical steam trap: ρ′MOR=0.8ρ′o (1)
Thermostatic steam trap: ρ′MOR=0.3ρ′o (2)
Thermodynamic steam trap:
Disc steam trap: ρ′MOR=0.5ρ′o (3)
Pulse steam trap: ρ′MOR=0.25ρ′o (4)
In the formula:
- ρ′MOR — the actual maximum working back pressure of the steam trap, Pa;
- ρ′o — The actual working pressure of the steam trap, Pa.
⑧ Determination of the actual working pressure ρ′o of the steam trap. When the condensed water is discharged from the steam pipeline system, the actual working pressure of the steam trap is equal to the working pressure of the steam pipeline.
When the condensed water is discharged from the steam-using equipment, the actual working pressure of the steam trap is determined by the following formula:
In the formula:
- ρ′o—actual working pressure of the steam trap, Pa ;
- ρ — steam pressure of steam-using equipment, Pa, its value is the measured data or the data provided by the manufacturer.
⑨ The actual working back pressure of the steam trap is determined by the following formula:
ρ′OR=gρ·(H3+△Z3)+ ρ3 (6)
In the formula:
ρ′OR—the actual working back pressure of the steam trap, Pa;
- H3—the total hydraulic resistance of the pipeline system behind the steam trap valve, Pa; value, if it drops to a negative value, m;
- Ρ3—the pressure of the condensate tank, Pa;
- g—the acceleration of gravity, m/s2;
- ρ—the density, kg/m3.
⑩ The condensate discharge rate used to select the steam trap is determined according to the following principles. It is necessary to accurately grasp the condensate discharge Gt and the steam pressure of the steam equipment.
It is used to select the condensed water discharge Gt of the steam trap, which is calculated according to the following formula:
In the formula, Gt—the condensed water discharge of the steam trap, t/h;
η—safety rate, its value Select according to the sample of steam trap, or refer to Table 2-9;
Gc—discharge of condensed water of steam-consuming equipment, t/h.
Choosing a good steam trap is an important energy-saving measure. According to the statistics of relevant departments of our country. At present, there are about 5 million steam traps in China. About 80% of the products fail to meet the requirement of the current national standard that the steam leakage is less than 3%. 15 million tons of standard coal will be lost every year. Therefore, it is necessary to select the appropriate steam trap for different working conditions in the country.
The performance of traps commonly used in my country is shown in Table 2-10.
Due to the influence of various factors, the theoretical calculation of the technical parameters of the trap is different from the actual use. The actual displacement is greater than the theoretical displacement. Its safety rate η is shown in Table 2-9.
In occasions where condensed water needs to be removed immediately, such as turbine steam engines, steam pumps, steam main pipelines, etc., it is not suitable to use traps with supercooling, such as pulse traps and thermostatic bellows traps.
Table 2-9 Safety rate η recommendation table for steam traps
|Serial number||Heating system||Usage||n|
|1||Drain the lower part of the sub-cylinder||Under various pressures, it can quickly remove condensed water||3|
|2||Steam main drain||
For the main pipeline conveying saturated steam, when the gas is supplied intermittently, start-up steam traps should be installed every 100m; -500m should be installed to start the steam trap. For the main pipe for conveying superheated
steam The bottom of the pipe, the end of the pipe, the front of the pressure reducing valve and the automatic regulating valve
|3||Branch pipe||Drainage points are set in front of various control valves where the branch pipe length is greater than or equal to 5m||3|
|4||Water separator||In the lower part of the steam separator||3|
|5||Tracer||Generally, the diameter of the heating pipe is DN15, and the drainage point is set at a place less than or equal to 50m||2|
|6||Heater||When the pressure is constant||3|
When the pressure is adjustable: less than or equal to 100kpa
|7||Single coil heating (liquid)||fast heating||3|
|No need for rapid heating||2|
|8||Multiple Parallel Coil Heating (Liquid)||2|
|9||Drying room (box)||
Higher pressure PN16 is used when the pressure is
constant and when the
pressure is adjustable
|10||Hydrophobicity of Lithium Bromide Refrigeration Equipment Evaporator||
Single effect pressure is less than or equal to 100kpa
Double effect pressure is less than or equal to 1MPa
|11||Thermal coils immersed in liquid||When the pressure is constant||2|
When the pressure is adjustable: 1 ~ 200 kpa,
greater than 200 kpa
|12||Shell and tube heat exchanger||When the pressure is constant||2|
When the pressure is adjustable: less than or equal to 100 kpa
101 ~ 200 kpa
greater than 200 kpa
|13||Jacketed pot||An air discharge valve must be installed above the jacketed pot||3|
|14||Single or multiple effect evaporator||
The amount of condensed water is less than or equal to 20t/h and
greater than 20t/h
|15||Laminator||Traps should be layered, pay attention to water hammer||3|
|16||Disinfection cabinet||There is an air discharge valve on the top of the cabinet||3|
|17||Rotary drying cylinder||
Surface linear velocity: less than or equal to 300m/s
|18||Secondary steam tank||The diameter of the tank body should ensure that the secondary steam velocity V≤5 m/s and an air exhaust valve must be installed on the tank body||3|
Note: See JBJ10-83 “Technical Regulations for Heating, Ventilation and Air Conditioning Design of Machinery Factory” for the air supply and heating part of the heater.
Table 2-10 Performance comparison of commonly used steam traps
|Project||Thermodynamic Steam Traps||Mechanical Traps||Thermostatic Steam Traps|
|Thermodynamic||Pulse||Bell float||Float||Float type||Bellows||
|Drainage performance||Intermittent drainage||Near continuous||Intermittent drainage||Near continuous||Intermittent drainage||Same left||Same left||Same left|
|exhaust performance||Better||It is good||Better||Not good||Not good||It is good||It is good||It is good|
|When the conditions of use change||Auto adapt||Need to adjust||Auto adapt||The weight of the buoy needs to be adjusted||Generally do not adjust||Should be adjusted|
|Allow back pressure||The allowable back pressure is 50% and the minimum working pressure is 0.05MPa||Allowable back pressure 25%||△ρ＞0.05MPa||Same left||Same left||Very low allowable back pressure||No need to adjust when the allowable back pressure is 50%||Allowable back pressure is extremely low, but can be increased with adjustment|
|Action performance||Sensitive and reliable||Sensitive, control cylinder is easy to get stuck||Slow, but regular and reliable||Same left||Same left||Slow, unreliable||Same left||Same left|
|Scope of application||Can be used for superheated steam||Same left||Only suitable for low pressure (0.2MPa)|
|Whether to antifreeze||Vertical installation prevents freezing||Don’t want||Want||Want||Want||Don’t want||Vertical installation prevents freezing||Same left|
|Start operation||Need to fill with water||Open the deflation valve to exhaust and fill with water|
|Installation direction||Level||Level||Level||Same left||Same left||Bellows telescopic direction||Level||Same left|
|Drain temperature||Close to saturation temperature||Same left||Same left||Same left||Same left||Below saturation temperature||Same left||Same left|
|Durability||Better||Poor||Faster valve and pin tip wear||Valve parts wear out faster||Poor||It is good||It is good|
|structure size||Small||Small||Bigger||Big||Big||Very small||Small||Small|
When the condensate is lower than 15% of the rated maximum displacement, the pulse trap should not be used, because under this condition, the fresh steam is easy to be lost from the discharge hole. In the surroundings of office buildings, schools, scientific research institutes and other buildings, a quiet environment is required, and it is not suitable to use thermal power traps with loud noises. Instead, thermal manager hi traps and float traps should be used, because of their slow action, Small impact and low noise.
For intermittently operated indoor steam heating equipment and pipelines, traps with good exhaust performance should be selected, such as inverted bucket or thermostatic traps.
Mechanical traps are generally not suitable for traps that work outdoors. When necessary, antifreeze protection measures should be taken.
Nine, the selection of general valve parameters
For the parameter tables of gate valves, globe valves, throttle valves, ball valves, butterfly valves, diaphragm valves, plug valves, check valves, pressure reducing valves and safety valves, see Table 2-11 – Table 2-20 respectively.
Table 2-11 Gate valve parameters
|Wedge double disc gate valve||Z42W-1||0.1||Gas||100||300-500|
|Bevel gear drive wedge double disc gate valve||Z542W-1||600-1000|
|Electric wedge double disc gate valve||Z942W-1||600-1400|
|Electric dark rod wedge double disc gate valve||Z946T-2.5||0.25||Water||1600, 1800|
|Electric dark rod wedge gate valve||Z945T-6||0.60||1200, 1400|
|wedge gate valve||Z41T-10||1.0||Steam, water||200||50-450|
|wedge gate valve||Z41W-10||Oil||200||50-450|
|Electric wedge gate valve||Z941T-10||Steam, water||200||100-450|
|Parallel double disc gate valve||Z44T-10||50-400|
|Parallel double disc gate valve||Z44W-10||Oil||100||50-400|
|Hydraulic wedge gate valve||Z741T-10||Water||100-600|
|Electric parallel double disc gate valve||Z944T-10||Steam, water||200||100-400|
|Electric parallel double disc gate valve||Z944W-10||Oil||100||100-400|
|Dark rod wedge gate valve||Z45T-10||Water||50-700|
|Dark rod wedge gate valve||Z45W-10||Oil||50-450|
|Spur gear driven dark rod wedge gate valve||Z455T-10||Water||800, 900, 1000|
|Electric dark rod wedge gate valve||Z945T-10||Water||100-1000|
|Electric dark rod wedge gate valve||Z945W-10||Oil||100450|
|wedge gate valve||Z40H-16C||1.6||Oil, steam, water||350||200-400|
|Electric wedge gate valve||Z940H-16C||200-400|
|Pneumatic wedge gate valve||Z640H-16C||200-500|
|wedge gate valve||Z40H-16Q||65-200|
|Electric wedge gate valve||Z940H-16Q||65-200|
|wedge gate valve||Z40W-16P||Nitric acid||100||200, 250, 300|
|wedge gate valve||Z40W-16I||Acetic acid||200, 250, 300|
|wedge gate valve||Z40Y-16I||Oil||550||200-400|
|wedge gate valve||Z40H-25||2.5||Oil, steam, water||350||50-400|
|Electric wedge gate valve||Z940H-25||50-400|
|Pneumatic wedge gate valve||Z640H-25||50-400|
|wedge gate valve||Z40H-25Q||50-200|
|Electric wedge gate valve||Z940H-25Q||50-200|
|Bevel gear drive wedge double disc gate valve||Z542H-25||2.5||Steam, water||300||300-500|
|Electric wedge double disc gate valve||Z942H-25||300-800|
|Socket welding wedge gate valve||Z61Y-40||4.0||Oil, steam, water||425||15-40|
|wedge gate valve||Z41H-40||15-40|
|wedge gate valve||Z40H-40||50-250|
|Spur gear drive wedge gate valve||Z400H-40||300, 350, 400|
|Electric wedge gate valve||Z940H-40||50-400|
|Pneumatic wedge gate valve||Z640H-40||50-400|
|wedge gate valve||Z40H-40||350||50-200|
|Electric wedge gate valve||Z940H-40Q||50-200|
|wedge gate valve||Z40Y-40P||Nitric acid||100||200, 250|
|Spur gear drive wedge gate valve||Z440Y-40P||300-500|
|wedge gate valve||Z40Y-40I||Oil||550||50-250|
|wedge gate valve||Z40H-64||6.4||Oil, steam, water||425||50-250|
|Spur gear drive wedge gate valve||Z440H-64||300, 350, 400|
|Electric wedge gate valve||Z940H-64||50-800|
|Electric wedge gate valve||Z940Y-64I||Oil||550||300, 350, 400, 450, 500|
|wedge gate valve||Z40Y-64I||10.0||Oil, steam, water||450||50-250|
|wedge gate valve||Z40Y-100||50-200|
|Spur gear drive wedge gate valve||Z440Y-100||250, 300|
|Electric wedge gate valve||Z940Y-100||50-300|
|Socket welding wedge gate valve||Z61Y-160||16.0||Oil||15-40|
|wedge gate valve||Z41H-160||15-40|
|wedge gate valve||Z40Y-160||50-200|
|Electric wedge gate valve||Z940Y-160||50-300|
|wedge gate valve||Z40Y-160I||550||50-200|
|Electric wedge gate valve||Z940Y-160I||50-200|
Table 2-12 Globe valve parameters
|Nominal diameter DN/mm|
|Rubber lined direct flow globe valve||J45J-6||0.6||Acid, alkali||50||40-150|
|Lead lined direct flow globe valve||J45Q-6||sulfuric acid||100||25-150|
|Welded Bellows Type Globe Valve||WJ61W-6P||Nitric acid||10-25|
|Bellows Type Globe Valve||WJ41W-6P||32, 40, 50|
|Internal thread globe valve||J11W-16||1.6||Oil||100||15-65|
|Internal thread globe valve||J11T-16||Steam, water||200||15-65|
|Shut-off valve||J41T-16||Steam, water||200||25-150|
|Shut-off valve||J41W-16P||Nitric acid||100||80-150|
|Shut-off valve||J41W-16R||Acetic acid||80-150|
|External thread globe valve||J21W-25K||2.5||Ammonia, ammonia liquid||-40-150||6|
|External thread angle globe valve||J24W-25K||6|
|External thread globe valve||J21B-25K||10-25|
|External thread angle globe valve||J24B-25K||10-25|
|Angle globe valve||J44B-25Z||32, 40, 50|
|Bellows Type Globe Valve||WJ41W-25P||2.5||Nitric acid||100||25-150|
|DC globe valve||J45W-25P||25-100|
|External thread globe valve||J21W40||4.0||Oil||200||6, 10|
|Ferrule stop valve||J91W-40||6, 10|
|Ferrule stop valve||J91H-40||4.0||oil, steam, water||425||15, 20, 25|
|Card sleeve angle globe valve||H94W-40||Oil||200||6, 10|
|Card sleeve angle globe valve||J94H-40||oil, steam, water||425||15, 20, 25|
|External thread globe valve||J21H-40||oil, steam, water||425||15, 20, 25|
|External thread angle globe valve||J24W-40||Oil||200||6, 10|
|External thread angle globe valve||J24H-40||oil, steam, water||425||15, 20, 25|
|External thread globe valve||J21W-40P||Nitric acid||100||6-25|
|External thread globe valve||J21W-40R||Acetic acid||6-25|
|External thread angle globe valve||J24W-40P||Nitric acid||6-25|
|External thread angle globe valve||J24W-40R||Acetic acid||6-25|
|Socket Weld Globe Valve||J61Y-40||oil, steam, water||425||10-25|
|Shut-off valve||J41W-40P||Nitric acid||100||32-150|
|Shut-off valve||J41W-40R||Acetic acid||32-150|
|Electric globe valve||J941H-40||oil, steam, water||425||50-150|
|Angle globe valve||J44H-40||425||32, 40, 50|
|Electric globe valve||J941H-64||50-100|
|Electric globe valve||J941H-100||50-100|
|Angle globe valve||J44H-100||32, 40, 50|
|Socket Weld Globe Valve||J61Y-160||16.0||oil||450||15-50|
|External thread globe valve||J21W-160||200||6, 10|
Table 2-13 Throttle valve parameters
|Nominal diameter DN/mm|
|External thread throttle valve||L21W-25K||2.5||Ammonia, ammonia liquid||-40-150||10, 25|
|External thread angle throttle valve||L24W-25K||10, 25|
|External thread throttle valve||L21B-25K||20, 25|
|External thread angle throttle valve||L24B-25K||20, 25|
|Throttle valve||L41B-25Z||2.5||Ammonia, ammonia liquid||-40-150||32, 40, 50|
|Angle throttle valve||L44B-25Z||32, 40, 50|
|External thread throttle valve||L21W-40||4.0||Oil||200||6, 10|
|Card sleeve throttle valve||L91W-40||6, 10|
|External thread throttle valve||L21W-40P||Nitric acid||6-25|
|External thread throttle valve||L21W40R||Acetic acid||6-25|
|External thread throttle valve||L21H-40||Oil, steam, water||425||15, 20, 25|
|Card sleeve throttle valve||L91H-40||15, 20, 25|
|Throttle valve||L41H-40Q||350||32, 40, 50|
|Throttle valve||L41W-40P||Nitric acid||100||32, 40, 50|
|Throttle valve||L41W-40R||Acetic acid||32, 40, 50|
|Throttle valve||L41H-100||10.0||Oil, steam, water||450||10-50|
Table 2-14 Ball valve parameters
|Nominal diameter DN/mm|
|Internal thread ball valve||Q11F-16||1.6||oil, water||100||15-65|
|ball valve||Q41F-16P||Nitric acid||100, 125, 150|
|ball valve||Q41F-16FR||Acetic acid||100, 125, 150|
|L-shaped three-way ball valve||Q44F-16Q||oil, water||15-150|
|T-shaped three-way ball valve||Q45F-16Q||15-150|
|Worm gear drive fixed ball valve||Q347F-25||2.5||150||200-500|
|Pneumatic fixed ball valve||Q647F-25||200-500|
|Electric fixed ball valve||Q947F-25||200-500|
|External thread ball valve||Q21F-40||4.0||10-25|
|External thread ball valve||Q21F-40P||Nitric acid||100||10-25|
|External thread ball valve||Q21F-40R||Acetic acid||10-25|
|ball valve||Q41F-40Q||oil, water||150||32-100|
|ball valve||Q41F-40P||Nitric acid||100||32-200|
|ball valve||Q41F-40R||Acetic acid||32-200|
|Pneumatic ball valve||Q641F-40Q||oil, water||150||50-100|
|ball valve||Q41N-64||6.4||oil, natural gas||80||50-100|
|Pneumatic ball valve||Q641N-64||50-100|
|Pneumatic fixed ball valve||Q647F-64||125, 150, 200|
|Electric fixed ball valve||Q947F-64||125-500|
|Electro-hydraulic fixed ball valve||Q247F-64||125-500|
|Pneumatic-hydraulic fixed ball valve||Q847F-64||125-500|
|Pneumatic-hydraulic welding fixed ball valve||Q867F-64||400-700|
|Electro-hydraulic welding fixed ball valve||Q267F-64||400-700|
Table 2-15 Butterfly valve parameters
|Nominal diameter DN/mm|
|Hydraulic butterfly valve||D741X-2.5||0.25||oil, water||50||2200-3000|
|Electric Butterfly Valve||D941X-2.5||1600-3000|
|Electric Butterfly Valve||D941X-6||0.6||1200, 1400,|
|Electric Butterfly Valve||D941X-10||1.0||250-1000|
|Pneumatic butterfly valve||D641X-10||250-1000|
|Worm gear drive butterfly valve||D341X-10||250-1000|
Table 2-16 Diaphragm valve parameters
|Nominal diameter DN/mm|
|Diaphragm valve||G41W-6||0.6||Acid, alkali||65||15-200|
|Rubber lined diaphragm valve||G41J-6||25-300|
|Pneumatic Rubber Lined Diaphragm Valve||G641J-6||25-200|
|Pneumatic normally open rubber-lined diaphragm valve||G6K41J-6||25-200|
|Pneumatic normally closed rubber-lined diaphragm valve||G6B41J-6||25-200|
|Electric Rubber Lined Diaphragm Valve||G941J-6||50-200|
|Enamel Diaphragm Valve||G41C-6||100||25-200|
Table 2-17 Plug valve parameters
|Nominal diameter DN/mm|
|Plug valve||X43W-6||0.6||Oil||100||100, 125, 150|
|T-shaped three-way plug valve||X44W-6||25-100|
|Internal Thread Plug Valve||X13W-10T||1.0||Water||15-50|
|Internal Thread Plug Valve||X13W-10||Oil||15-50|
|Internal Thread Plug Valve||X13T-10||Water||15-50|
|Oil seal T-shaped three-way plug valve||X46W-10||Oil||25-, 100|
|Oil Sealed Plug Valve||X47W-16||1.6||25-150|
|Plug valve||X43W-16I||Sandy oil||580||50-125|
Table 2-18 Check valve parameters
|Nominal diameter DN/mm|
|Internal thread lift bottom valve||H12X-2.5||0.25||Water||50||50, 65, 80|
|Lifting bottom valve||H42X-2.5||50-300|
|Swing double disc bottom valve||H46X-2.5||350-500|
|Swing multi disc check valve||H45X-2.5||1600, 1800|
|Swing multi disc check valve||H45X-6||0.6||1200, 1400|
|Swing multi disc check valve||H45X-10||1.0||700-1000|
|Swing Check Valve||H44X-10||50-600|
|Swing Check Valve||H44T-10||Steam, water||200||50-600|
|Swing Check Valve||H44W-10||Oil||100||50-450|
|Internal thread lift check valve||H11T-16||1.6||Steam, water||200||15-50|
|Internal thread lift check valve||H11W-16||Oil||100||15-50|
|Lift check valve||H41T-16||Steam, water||200||25-200|
|Lift check valve||H41W-16||Oil||100||25-200|
|Lift check valve||H41W-16P||Nitric acid||80-150|
|Lift check valve||H41W-16R||Acetic acid||80-150|
|External thread lift check valve||H21B-25K||2.5||Ammonia, ammonia liquid||-40-150||15, 20, 25|
|Lift check valve||H41B-25Z||32, 40, 50|
|Swing Check Valve||H44H-25||350||200-500|
|Lift check valve||H41H-40||4.0||Oil, steam, water||425||10-150|
|Lift check valve||H41H-40Q||350||32-150|
|Swing Check Valve||H44H-40||425||50-400|
|Swing Check Valve||H44Y-40I||Oil||550||50-250|
|Swing Check Valve||H44W-40P||Nitric acid||100||200-400|
|External thread lift check valve||H21W-40P||15, 20, 25|
|Lift check valve||H41W-40P||32-150|
|Lift check valve||H41W-40R||Acetic acid||32-150|
|Lift check valve||H41H-64||6.4||oil, steam, water||425||50-100|
|Swing Check Valve||H44H-64||50-500|
|Swing Check Valve||H44Y-64I||Oil||550||50-500|
|Lift check valve||H41H-100||10||oil, steam, water||450||10-100|
|Swing Check Valve||H44H-100||50-200|
|Swing Check Valve||H44H-160||16||oil, water||50-300|
|Swing Check Valve||H44Y-160I||oil||550||50-200|
|Lift check valve||H41H-160||450||15-40|
|Socket welding lift check valve||H61Y-160||15-40|
Table 2-19 Pressure reducing valve parameters
|Nominal diameter DN/mm|
|Direct acting bellows pressure reducing valve||Y41T-10||1.0||Steam, air||180||0.05-0.4||20-50|
|Direct acting thin film pressure reducing valve||Y12N-40||4.0||Air||-40-70||0.05-2.5||25-80|
|Direct acting thin film pressure reducing valve||Y42X-40||4.0||water, air||70||1-2.5||25-80|
|Direct acting thin film pressure reducing valve||Y42X-64||6.4||water, air||70||1-2.5||25-50|
|Pilot Piston Pressure Reducing Valve||Y43H-16||1.6||Steam||200||0.05-1.0||20-300|
|Pilot Piston Pressure Reducing Valve||Y43H-16Q||Steam||300||0.05-1.0||200-300|
|Pilot Piston Pressure Reducing Valve||Y43F-16Q||Water||0-70||0.1-1.0||20-300|
|Pilot Piston Pressure Reducing Valve||Y43X-16Q||Air||-40-70||0.05-1.0||20-300|
|Pilot Piston Pressure Reducing Valve||Y43H-25||2.5||steam||350||0.1-1.6||25-300|
|Pilot Piston Pressure Reducing Valve||Y43F-25||2.5||Water||0-70||0.1-1.6||25-100|
|Pilot Piston Pressure Reducing Valve||Y43X-40||4.0||Air||-40-70||0.1-1.6||25-200|
|Pilot Piston Pressure Reducing Valve||Y43H-40||Steam||400||0.1-2.5||25-200|
|Pilot Piston Pressure Reducing Valve||Y43F-40||Water||0-70||0.1-2.5||25-80|
|Pilot Piston Pressure Reducing Valve||Y43X-40||Air||-40-70||0.1-2.5||25-100|
|Pilot Piston Pressure Reducing Valve||Y43H-64||6.4||Steam||450||0.5-3.5||25-100|
|Pilot Piston Pressure Reducing Valve||Y43F-64||Water||0-70||0.5-3.5||25-50|
|Pilot Piston Pressure Reducing Valve||Y43X-64||Air||-40-70||0.5-3.5||25-50|
|Pilot bellows pressure reducing valve||Y44H-16||1.6||Steam, air||200||0.1-1.4||20-50|
|Pilot film pressure reducing valve||Y45X-16C||Water||50||0.05-10||25-300|
|Pilot film pressure reducing valve||Y45H-16||Steam, air||250||0.02-1.5||25-300|
Table 2-20 Safety valve parameters
|Nominal diameter DN/mm|
|External thread spring safety valve||A27W-10T||1.0||0.4-1.0||Air||120||15-20|
|External thread spring type safety valve with wrench||A27H-10K||0.1-1.0||Air, steam, water||200||10-40|
|Spring type safety valve with wrench||A47H-16||1.6||0.1-1.6||40-100|
|External thread spring closed safety valve||A21H-16C||Air, ammonia gas, water, ammonia liquid||10-25|
|External thread spring closed safety valve||A21W-16P||Nitric acid etc.||10-25|
|Spring closed safety valve||A41H-16C||Air, ammonia gas, water, ammonia liquid, oil||300||32-80|
|Spring closed safety valve||A41W-16P||Nitric acid etc.||200||32-80|
|Spring type safety valve with wrench||A47H-16C||Air, steam, water||350||40-80|
|Double spring closed safety valve||A43H-16C||Air, steam||80-100|
|Spring full lift safety valve||A40H-16C||Oil, air||450||50-150|
|Spring full lift safety valve||A40Y-16I||550||50-150|
|Spring closed full lift safety valve||A42H-16C||0.06-1.6||300||40-200|
|Spring closed full lift safety valve||A42W-16P||Nitric acid etc.||200||40-200|
|Spring closed full lift safety valve with wrench||A44H-16C||0.1-1.6||Oil, air||300||50-150|
|Spring full lift safety valve||A48H-16C||Air, steam||350||50-150|
|External thread spring closed safety valve||A21H-40||4.0||1.6-4.0||Air, ammonia gas, water, ammonia liquid||200||15-25|
|External thread spring closed safety valve||A21W-40P||Nitric acid etc.||15-25|
|Spring closed safety valve||A41H-40||1.3-4.0||Air, ammonia gas, water, ammonia liquid, oil||300||32-80|
|Spring closed safety valve||A41W-40P||1.6-4.0||Nitric acid etc.||200||32-80|
|Spring type safety valve with wrench||A47H-40||1.3-4.0||Air, steam||350||40-80|
|Double spring closed safety valve||A43H-40||80-100|
|Spring full lift safety valve||A40H-40||0.6-4.0||Oil, air||450||50-150|
|Spring full lift safety valve||A40Y-40I||550||50-150|
|Spring closed full lift safety valve||A42H-40||1.3-4.0||300||40-150|
|Spring closed full lift safety valve||A42W-40P||1.6-4.0||Nitric acid etc.||200||40-150|
|Spring closed full lift safety valve with wrench||A44H-40||1.3-4.0||Oil. Air||300||50-150|
|Spring full lift safety valve||A48H-40||Air. steam||350||50-150|
|Spring closed safety valve||A41H-100||10||3.2-10||Air, water, oil||300||32-50|
|Spring full lift safety valve||A40H-100||1.6-8.0||Oil, air||450||50-100|
|Spring full lift safety valve||A40Y-100I||550||50-100|
|Spring full lift safety valve||A40H-100P||600||50-100|
|Spring closed full lift safety valve||A42H-100||3.2-10||Nitrogen, hydrogen, Oil, air||300||40-100|
|Spring closed but wrench fully opened safety valve||A44H-100||Oil, air||50-100|
|Spring full lift safety valve||A48H-100||Air, steam||350||50-100|
|Spring closed safety valve||A41H-160||16||10-16||Air, nitrogen and hydrogen, water, oil||200||15-32|
|Spring full lift safety valve||A40H-160||Oil, air||450||50-80|
|Spring full lift safety valve||A40Y-160I||550||50-80|
|Spring full lift safety valve||A40Y-160P||600||50-80|
|Spring closed full lift safety valve||A42H-160||Nitrogen, hydrogen, Oil, air||300||15, 32-80|
|Spring closed safety valve||A41H-320||32||16-32||Air, nitrogen and hydrogen, water, oil||200||15-32|
|Spring closed full lift safety valve||A42H-320||Nitrogen, hydrogen, Oil, air||300||32-50|
How to purchase valves?
It is important to choose the most suitable valve for pipeline system, which is related to the safety of pipeline, flow loss, cost, etc. You must be familiar with the characteristics of the valve and the steps and basis for selecting the valve.
The main problems of the valve market for:
- First, some operators buy valves without factory name and address, print the famous manufacturer’s brand name and certificate of conformity, the reputation of qualified valve companies caused serious harm.
- Second, refurbished valves, some operators through the second sale of used valves after repainting, to the quality of the project brings serious safety risks.
Therefore, you should be careful in choosing the right valve door for your purpose. To avoid ambiguity, precise specifications should be made for each valve. When asking for quotations or ordering, a comprehensive and appropriate description of the valve required should be made.
The characteristics of the valve are use characteristics and structural characteristics.
Use characteristics determine the main performance and use of the valve, belonging to the valve use characteristics are: the type of valve (closed-circuit valves, regulating valves, safety valves, etc.); product type (gate valves, globe valves, butterfly valves, ball valves, etc.)
Valve main parts (valve body, valve cover, valve stem, valve flap, sealing surface) of the material; valve transmission mode, etc..
Structural characteristics it determines the valve installation, repair, maintenance and other methods of some structural characteristics, belonging to the structural characteristics are: the structure of the valve length and overall height, the form of connection with the pipeline (flange connection, threaded connection, clamped hoop connection, external threaded connection, welded end connection, etc.)
The form of sealing surface (inlay ring, threaded ring, overlay welding, spray welding, valve body body); the form of stem structure (rotary rod, lift rod), etc.
The steps to purchase valves.
Define the use of the valve in the equipment or device, determine the working conditions of the valve: applicable media, working pressure, working temperature, etc..
Determine the nominal diameter of the pipeline connected to the valve and the connection: flange, threaded, welded, etc.
Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electro-hydraulic linkage, etc.
Determine the material of the shell and inner parts of the selected valve according to the medium, working pressure and working temperature of the pipeline: cast steel, carbon steel, stainless steel, alloy steel, stainless acid-resistant steel, gray cast iron, malleable cast iron, ductile iron, copper alloy, etc.
Selecting the type of valve: closed circuit valve, regulating valve, safety valve, etc.; determining the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.
Determine the parameters of the valve: for automatic valves, first determine the allowable flow resistance, discharge capacity, back pressure, etc., according to different needs, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.
Determine the geometric parameters of the selected valve: structure length, flange connection form and size, the size of the valve height direction after opening and closing, the size and number of connected bolt holes, the entire valve external dimensions, etc.; use the available information: valve catalogs, valve product samples, etc. to select the appropriate valve products.
Valve procurement only clear specifications, categories, work pressure to meet the procurement requirements of the practice, in the current market economy is not perfect. Because the valve manufacturers in order to product competition, each in the valve under the concept of unified design, different innovations, the formation of their own corporate standards and product personality. Therefore, the more detailed technical requirements in the procurement of valves, and manufacturers to coordinate to achieve consensus, as the valve procurement contract is very necessary.
General requirements of the valve
Valve specifications and categories, should be in line with the requirements of the pipeline design documents.
The model number of the valve should indicate the requirements based on the national standard number. If it is a corporate standard, the relevant description of the model should be indicated.
Valve working pressure, required ≥ the working pressure of the pipeline, without affecting the price of the premise that the valve can withstand the pressure should be greater than the actual pressure of the pipeline; valve closed condition of any side should be able to withstand 1.1 times the valve pressure value without leakage; valve open condition, the valve body should be able to withstand two times the valve pressure requirements.
Valve manufacturing standards, should state the national standard number based on, if it is a corporate standard, the procurement contract should be attached to the corporate documents.
Material of the valve
Valve body material, should be mainly ductile iron, and specify the grade and the actual physical and chemical testing data of cast iron.
Stem material, strive for stainless steel stem (2CR13), large diameter valves should also be stainless steel embedded stem.
Nut material, using cast aluminum brass or cast aluminum bronze, and hardness and strength are greater than the stem.
Stem bushing material, its hardness and strength should be no greater than the stem, and in water immersion conditions and the stem, the body does not form electrochemical corrosion.
Material of sealing surface
- ① Valve categories vary, sealing methods and material requirements vary.
- ② Ordinary wedge gate valve, the material of copper ring, the way of fixing, grinding should be stated.
- ③ Soft seal gate valve, the physical chemical and health testing data of the valve plate lining material.
- ④ Butterfly valve should indicate the material of the sealing surface on the valve body and the material of the sealing surface on the butterfly plate; their physicochemical test data, especially the health requirements of rubber, anti-aging properties, wear resistance; usually using nitrile rubber and EPDM rubber, etc., is strictly prohibited to mix with recycled rubber.
Valve spindle packing
- ① As the valves in the pipeline network, usually open and close infrequently, the packing is required to be inactive for several years, and the packing is not aging, to maintain long-term sealing effect.
- ② Valve spindle packing should also withstand frequent opening and closing, the good sealing effect.
- ③ In view of the above requirements, the valve spindle packing should not be replaced for life or for more than ten years.
- ④ If the packing needs to be replaced, the valve design should consider the measures to replace it under the condition of water pressure.
Variable speed transmission box
Box material and internal and external anti-corrosion requirements and the principle of the valve body consistent.
Box should have sealing measures, box assembly can withstand the immersion of 3 m water column condition.
Box on the opening and closing limit device, its adjustment nut should be in the box or located outside the box, but need special tools to work.
Transmission structure design is reasonable, open and close only drive the valve shaft rotation, not to make it up and down, transmission parts bite moderate, do not produce with load open and close when the separation of slippage.
Variable speed transmission box body and valve shaft seal can not be connected into a leak-free whole, otherwise there should be reliable anti-string leakage measures.
No debris in the box, gear bite parts should be protected by grease.
Valve operating mechanism
The direction of opening and closing the valve operation, all should be closed clockwise.
As the valve in the network, often manually open and close, open and close the number of revolutions should not be too much, that is, large diameter valves should also be within 200-600 revolutions.
In order to facilitate the opening and closing operation of a person, in the pipeline pressure condition, the maximum opening and closing torque should be 240N-m.
Valve opening and closing operation end should be square dovetail, and standardized size, and facing the ground, so that people from the ground can be directly operated. Valves with wheel discs are not suitable for underground pipeline networks.
Valve opening and closing degree of the display panel
- ① Valve opening and closing degree of the scale, should be cast in the gearbox cover or switch the direction of the display disk on the shell, all facing the ground, the scale line brushed with phosphor to show eye-catching;.
- ② Indicate the material of the dial needle in the case of better management available stainless steel plate, otherwise painted steel plate, do not use aluminum skin production.
- ③ Indicate the disc needle eye-catching, fixed firmly, once the opening and closing adjustment is accurate, should be locked with rivets.
If the valve is buried deeper, the operating mechanism and display disk from the ground distance ≥ 1.5m, should be equipped with extension pole facilities, and fixed stable and firm, so that people from the ground to observe and operate. In other words, the valve opening and closing operation in the network, should not be down the well operation.
Valve performance testing
Valve a specification batch manufacturing, should be entrusted to authoritative institutions for the following performance testing.
- ① Valve opening and closing torque under working pressure conditions.
- ② In the case of pressure, to ensure that the valve closes tightly the number of continuous opening and closing.
- ③ Valve in the pipeline under the condition of the flow resistance coefficient of detection.
Valve in the factory before the following tests should be carried out.
- ① Valve in the open condition, the valve body should withstand two times the valve pressure value of the internal pressure test.
- ② Valve in the closed condition, both sides are subjected to 1.1 times the valve pressure value, no leakage; but the metal seal butterfly valve, leakage value is not greater than the relevant requirements.
Valve internal and external corrosion
Valve body (including variable speed transmission box body) inside and outside, the first should be shot blasting and sand removal, and strive to electrostatic spraying powder non-toxic epoxy resin, the thickness of 0.3mm or more. When it is difficult to electrostatically spray non-toxic epoxy resin for very large valves, it should also be brushed and sprayed with similar non-toxic epoxy paint.
The internal part of the valve body and various parts of the valve plate require comprehensive anti-corrosion, on the one hand, it will not rust when immersed in water, and no electrochemical corrosion will occur between the two metals; on the other hand, the surface is smooth so that the water resistance is reduced.
The valve body anti-corrosion epoxy resin or paint health requirements, there should be the corresponding authority’s test report. Chemical physical properties should also meet the relevant requirements.
Valve packaging and transportation
Both sides of the valve should be set up with a light blocking plate to seal.
Medium and small diameter valves should be bundled with straw rope, and the container mode of transport is appropriate.
Large-diameter valves also have a simple wooden frame solid packaging to avoid damage during transportation.
Factory manual of the valve
Valve is the equipment, in the factory manual should be marked with the following relevant data.
Valve specifications; model; working pressure; manufacturing standards; valve body material; stem material; sealing material; spool packing material; stem sleeve material; internal and external anti-corrosion material; operation start direction; number of revolutions; work pressure condition opening and closing torque; manufacturer’s name; factory date; factory number; weight; connecting flange aperture, number of holes, center hole distance; graphically indicate the overall length, width and height of the control dimensions. Valve flow resistance coefficient; effective number of openings and closings; valve factory test data and installation, maintenance considerations.
Valve standards and specifications that should be understood
Standards for the design and manufacture of valves.
- API 6D “pipeline valves”
- API 608 “Metal ball valves with flanged, threaded, and welded connections”
- ASME B16.34 “Valves with flanged, threaded, and welded connections”
- ANSI/AWWA C507 “6-inch to 48-inch ball valves”
- BFCI 70-2 “Control Valve Seat Leaks”
- MSS SP-72 “Ball valves for general use with flanged and butt-welded connections”
- BS 5351 “Steel ball valves for petroleum, petrochemical and related industries”
- BS 6364 “Cryogenic valves”
- NACE MR0175 “Metallic materials for oilfield equipment resistant to vulcanization stress cracking”
- GB／T12237 “General purpose valves Flange and butt-weld connection steel ball valves”
- GB／T15185 “Iron and copper ball valves”
- JB／T 7745 “Pipeline ball valve”
- ISO 5211 “Partial rotary valve drive connection “
Standards for valve connection end dimensions.
- ASME B16.5 “Pipeline flanges and flanged fittings”
- ASME B16.47 “Large Diameter Steel Flanges NPS26 through NPS60”
- API 605 “Large Diameter Carbon Steel Flanges”
- MSS SP-44 “Steel pipe flanges”
- ISO 7005-1 “Metal flanges Part 1 Steel flanges”
- GB／T 9112-9124 “Steel pipe flanges”
- GB／T 13402 “Large diameter carbon steel pipe flange”
- HG 20592-20635 “Steel pipe flange”
- SH 3406 “petrochemical steel pipe flange”
- JB／T 74-90 “Pipe flanges”
- JIS B2238 “General rules for steel pipe flanges”
- ASME B16.25 “Butt weld ends”
- ASME B 16.11 “Forged fittings with socket weld and threaded connections”
- BS 12627 “Industrial valves Butt weld ends for steel valves”
- BS 12760 “Valves Steel valves with socket weld ends”
Standards for testing and inspection of valves.
- API 598 “Inspection and testing of valves”
- API 6D “Pipeline valves”
- API 607 “turn 1/4 week soft seat valve fire resistance test”
- API 6FA “valve fire resistance test specification”
- GB / T 13927 “general valve pressure test”
- JB / T 9092 “valve inspection and test”
- JB / T 6899 “fire resistance test of valves”
- BS 6755 Part 1 “Test of valves Part 1 Product pressure test requirements specification”
- BS 6755 Part 2 “Testing of valves Part 2 Code of requirements for the combustion test”
- BS 12569 “Industrial valves Requirements and tests for valves for the chemical and petrochemical processing industry”
- MSS SP-82 “Pressure test methods for valves”
- MSS SP-61 “Pressure testing of steel valves”
- MSS SP-55 “valves, flanges, fittings and other piping components of cast steel surface inspection of surface defects assessment”
Standards for structural length of valves.
- ASME B16.10 “Structural Length of Valves”
- ISO 5752 “Flange-connected metal valves Structural lengths”
- BS 558 “Industrial valves Structural lengths of metal valves for flange-connected piping systems”
- BS 12982 “Industrial valves Structural length of valves with butt-weld ends”
- GB／T 12221 “Flange-connected metal valves Structural length”
- GB / T 15188.1 “structural length of the valve butt-weld connection valve weld end”
If the requirements of the purchased valves conflict with the requirements of the technical agreement standards, clarification should be sought from the buyer before processing and manufacturing or procurement.
The basis for purchasing valves
The purpose of the selected valve, the conditions of use and the manipulation and control mode.
The nature of the working medium: working pressure, working temperature, corrosive properties, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive media, the viscosity of the medium, etc.
Requirements for the fluid characteristics of the valve: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
Installation size and form factor requirements: nominal diameter, connection to the pipeline and connection size, form factor or weight limit, etc.
Additional requirements for the reliability of the valve product, service life and explosion-proof performance of the electric device (in the selection of parameters should be noted: if the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop at closing, maximum and minimum inlet pressure of the valve).
According to the above basis and steps for selecting valves, reasonable and correct selection of valves must also be a detailed understanding of the internal structure of the various types of valves to be able to make the right choice of the preferred valve. The control of the pipeline is the valve. Valve opening and closing pieces control the way the medium flows in the pipeline, the shape of the valve flow channel so that the valve has certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.
Marking and identification of valves
Usually, according to the signs and signs on the valve and the paint on the valve, the type, structure, material, nominal diameter, nominal pressure (or working pressure), applicable medium, temperature and closing direction of the valve can be directly identified.
1. Understanding of signs
The label is fixed on the valve body or the handwheel. The data on the label is relatively complete, reflecting the basic characteristics of the valve . The manufacturer on the label can provide valve wearing parts, drawings and materials. According to the conditions of use provided on the label, the gasket to be replaced, the type and material of packing, and the material of other parts to be replaced can be determined.
2. The sign of the valve
1). Markings for general valves
The mandatory and optional marking items for general valves are shown in Table 3-1.
The specific markings for general valves are as follows:
(1) Items 1 to 4 in Table 3-2 are mandatory markings. For valves with DN≥50mm, they should be marked on the valve body; for valves with DN<50mm, they should be marked on the valve body. Or on the label, specified by the product designer.
(2) Items 5 and 6 in Table 3-2 are signs that must be used only when there is such a regulation in a certain type of valve standard, and they should be marked on the valve body and flange respectively.
(3) If there are no special regulations in various valve standards. Items 7 to 19 in Table 3-2 are signs that can be selected and used according to needs. When required, it can be marked on the valve body or on the plate.
Table 3-1 Marking items for general valves (GB12220-89)
|Project||The sign||Project||The sign||Project||The sign|
|1||Nominal diameter (DN)||8||Thread code||15||Lining material code|
|2||Nominal pressure (PN)||9||ultimate pressure||16||Quality and test marks|
|3||Material code of pressure parts||10||Factory No.||17||Inspector’s stamp|
|4||Manufacturer’s name or trademark||11||Standard||18||Manufacturing year, month|
|5||Arrows in the direction of medium flow||12||Furnace No.||19||Flow characteristics|
|6||Seal ring (pad) code||13||Internal material code|
|7||Limit temperature(℃)||14||Work station number|
Note: The nominal pressure casting mark value on the valve body is equal to 10 times the number of megapascals (MPa). When it is set below the value of the nominal diameter, it is not preceded by the code “PN”.
(4) Additional marks
- ① Any one of the marks in the table can be added at different positions. For example: Any sign set on the valve body can also be set repeatedly on the label.
- ② As long as the additional signs are not confused with the marks in the table, any other signs may be added. For example: product model, etc.
For pressure reducing valves, besides the requirements in Table 3-2, the marks on the valve body should also include: a. Date of manufacture; b. Applicable medium; c. Outlet pressure.
The signs of the steam traps shall be in accordance with the regulations in Table 3-2, and the signs may be set on the valve body or on the nameplate.
The signs of the safety valve shall be in accordance with the regulations in Table 3-3.
Table 3-2 Signs of steam traps (GB12249-89)
|Project||Required sign||Project||Required sign|
|1||Product number||1||Body material|
|2||Nominal diameter||2||Maximum allowable pressure|
|3||Nominal pressure||3||Maximum allowable temperature|
|4||Manufacturer’s name and trademark||4||Maximum discharge temperature|
|5||Arrows indicating the direction of medium flow||5||Factory serial number, date|
Table 3-3 Signs of safety valves (GB12241-89)
|Project||Logo on the valve body||Project||Logo on the valve body|
|1||Nominal diameter DN||1||Allowable maximum working temperature of valve design (°C)|
|2||Body material||2||Set pressure (MPa)|
|3||Manufacturer’s name and trademark||3||Standard No.|
|4||When the size or pressure level of the inlet and outlet connection parts are the same, there should be an arrow indicating the flow direction of the medium||4||Base model of the manufacturer|
|–||–||5||Rated displacement coefficient or rated displacement for reference medium|
|–||–||6||Runner area (mm2)|
|–||–||7||Opening height (mm)|
|–||–||8||percent over pressure|
2. Signs of power station valves
The general signs of power station valves can refer to the provisions of GB12220-89.
Qualified products of power station valves should be nailed with metal signs, and the contents of the signs are shown in Table 3-4.
Table 3-4 Marks on the valve plate of the power station (JB/T3595-93)
|Project||The sign||Project||the sign||Project||The sign|
|1||product name||4||Nominal diameter||7||Body material|
|2||Product model or drawing number||5||Nominal pressure or working pressure||8||date of manufacture|
|3||product number||6||working temperature||9||Manufacturer name|
For regulating valves, the marks on the nameplate should be in addition to the provisions in Table 3-4:
- ① Maximum allowable pressure difference;
- ② Rated flow coefficient of the product. The marks on the safety valve label shall comply with the provisions in Table 3-5.
Table 3-5 Marks on safety valve label (ZBJ98013-89)
|Project||The sign||Project||The sign||Project||The sign|
|1||Name and model of safety valve||4||Nominal pressure||7||Emission factor|
|2||Serial number||5||Throat diameter of valve seat||8||Manufacturer’s name or logo (registered trademark)|
|3||Date of Manufactory||6||Opening height||9||Proper temperature|
3. Sign of the opening and closing direction of the
handwheel There is an arrow indicating the closing direction of the valve on the handwheel and the word “close”.
4. Marking of the opening and closing groove of the
valve There is a groove engraved on the end face of the square head of the ball valve, the butterfly valve stem and the cock cone of the plug valve. The direction is perpendicular to the direction of the inlet and outlet of the valve , indicating that the valve is closed.
The passages of the opening and closing parts of the three-way valve are L-shaped and T-shaped, and the engraved L-shaped or T-shaped groove marks are consistent with the direction of the opening and closing parts. Through the direction of the groove, the valve switching and switching conditions can be judged.
5. Signs indicating the opening of the
valve Throttle valves, hidden stem gate valves, regulating valves, butterfly valves and other valves are equipped with opening indicators that reflect the degree of opening and closing of the valves. The opening indicator has a disc type, a scale type, etc., and is assembled on the handwheel, valve stem, and bracket. When the opening indicator is zero, it means the valve is closed.
6. Sign of the material code of the pressure parts The material code of the
pressure parts is marked on the valve body.
Identification of valve painting
Before the valve products leave the factory, different parts of the valve should be painted with different colors of paint according to the material of the valve body, the material of the sealing surface and the transmission mechanism, so as to facilitate identification.
The material identification of the valve body is to paint the unprocessed surface of the valve body and bonnet, and the paint color is as specified in Table 3-6.
The seal surface identification paint is painted on the transmission handwheel, handle or wrench, and the paint color is as specified in Table 3-7.
The paint color of the transmission mechanism is stipulated as follows: the electric device, ordinary type is painted with medium gray; the three-in-one (outdoor, explosion-proof, anti-corrosion) type is painted with sky blue; other transmission mechanisms such as pneumatic, hydraulic, and gear transmission are painted with the same color as valve products.
Table 3-6 Valve body material identification