What is a control valve?
Table of Contents
- What is a control valve?
- Selection of regulating valve type
- Characteristics and correct selection of standard regulating valve
- Selection of special regulating valve
- Selection of accessories
- Working principle of pneumatic control valve:
- Structure characteristics and working principle of electric control valve
- Working principle of self operated regulating valve
- Difference and selection of electric control valve and pneumatic control valve
- Difference between pneumatic control valve and self operated control valve
The regulating valve, also known as the control valve, is the terminal executive component in the industrial process control system. In the industrial process continuous production automatic control system, the regulating valve is generally used to control various process parameters in the process production, so as to achieve the adjustment of the parameters such as the pressure, temperature, flow and liquid level of the fluid. It is usually called “hand and foot” in the industrial process automation production. Its application quality is directly reflected in the regulation quality of the system. As a terminal executive component in process control, people have a deeper understanding of its importance than in the past. In addition to the quality of products and the correct installation, use and maintenance of users, it is very important to correctly calculate and select the type of regulating valve. Due to the error of calculation and selection, the system operation is not stable, some even can not be put into use. Therefore, users and system designers should fully realize the importance of the control valve in the field, and pay enough attention to the selection of the control valve.
The general principle of regulating valve selection is: on the premise of meeting the use function, the selected regulating valve shall have simple structure, reliable performance, low price, long service life, convenient maintenance, etc. The following focuses on the selection of regulating valve type and accessories.
There are many classification methods for regulating valves. At present, a classification method commonly used at home and abroad is based on structure, principle and function, which is divided into nine categories, namely, straight single seat regulating valve, straight double seat regulating valve, sleeve regulating valve, angle regulating valve, three-way regulating valve, diaphragm valve, butterfly valve, ball valve and eccentric rotary valve. These nine categories of products are the most basic and common products It is also known as standard product. Other products based on the improvement of practical application are called special products.
Characteristics and correct selection of standard regulating valve
Through single seat regulating valve
The straight through single seat regulating valve has only one valve core and one valve seat, which is easy to achieve strict sealing. The hard sealing of metal and metal, or the soft sealing of metal and polytetrafluoroethylene or other composite materials can be used. The standard leakage is 0.01% C (C is the rated flow coefficient). The allowable pressure difference is small, and the flow capacity is small. For example, the allowable pressure difference of DN100 single seat regulating valve is only 120kPa, and the flow capacity is only It is 100. The flow path is complex and the structure is simple, which is suitable for the occasions of clean medium with strict leakage requirements and small working pressure difference. However, the small size regulating valve (DN1 / 2, 3 / 4, 20) can also be used for the occasions with large pressure difference, which is one of the most widely used regulating valves. When further designed, it can be used as a shut-off valve. The flow characteristics are determined by the shape of the valve core. After being washed out, the original characteristics will be lost. Changing the valve core can change the flow characteristics. However, the thrust of the fluid medium to the valve core is large, that is, the unbalanced force is large, and the actuator with large thrust is required. Therefore, this kind of regulating valve should not be used in the application of high pressure difference and large caliber. When selecting this valve, special attention shall be paid to the check of differential pressure to prevent it from being jacked open.
Through double seat regulating valve
The straight through double seat regulating valve has two valve cores and two seats. Because the upward thrust of the upper valve core and the downward thrust of the lower valve core are basically balanced, the imbalance force of the whole valve core is small, and the allowable pressure difference is large. For example, the allowable pressure difference of the DN100 double seat regulating valve is 280kpa, and the flow capacity is large. Compared with other regulating valves of the same caliber, the double seat regulating valve can flow more fluid, with the same port The flow capacity of double seat regulating valve is 20% – 50% larger than that of single seat regulating valve. For example, the flow capacity of DN100 double seat regulating valve is 160. Therefore, in order to obtain the same flow capacity, the double seat control valve can choose the actuator with smaller thrust. The double seat regulating valve adopts top and bottom double guide, so it is convenient to refit the body valve and the anti body valve, that is, the body valve can be changed into the anti body valve or the anti body valve can be changed into the body valve by reversing the installation of the valve core and the valve seat, without changing the positive or negative action type of the actuator. The upper and lower valve cores of the double seat regulating valve can not be closed at the same time, so the leakage is large, and the standard leakage is 0.1% C (C is the rated flow coefficient); the flow path is complex, so it is not suitable for the application of high pressure difference, because in this application, the valve is severely scoured by high pressure fluid, and it is easy to form flash and cavitation, which aggravates the scour on the valve body, so it is not applicable In the control of fibrous media and high viscosity fluids.
Sleeve control valve
Sleeve regulating valve is also called cage valve. Its valve trim adopts valve core and cage (sleeve). The sleeve can be straight through single seat regulating valve, or double seat regulating valve or angle regulating valve. There are two structures: single seal and double seal. The former is equivalent to single seat regulating valve, which is suitable for single seat regulating valve; the latter is equivalent to double seat regulating valve, which is suitable for double seat regulating valve. In addition, it has the characteristics of good stability, convenient loading and unloading, convenient maintenance, noise reduction and cavitation reduction. However, the price is 50% – 200% higher than that of single seat and double seat control valves. It also needs special winding gasket, which is widely used, next to single seat and double seat control valves. However, this valve should not be used for unclean media and easy crystallization, stumbling and scaling media.
Angle control valve
Angle control valve is a single seat control valve with a special valve body structure, which is suitable for special piping and fluid occasions. It changes the straight valve body into an angle (equivalent to an elbow) valve body, and its throttling and stress forms are completely equivalent to the single seat control valve. The single seat control valve has the characteristics of small leakage and small differential pressure. In addition, because of its simple flow path with “self-cleaning” performance, it can be applied to unclean media, and can be further improved to anti blocking angle valve, which is suitable for the working conditions with suspended particles, especially in the situation where the installation space is limited.
Three way regulating valve
The three-way regulating valve is guided by the valve core itself. When replacing the air opening and air closing, the actuator must be replaced. It should be noted that the meaning of the air opening and air closing is different from other regulating valves. The air opening and air closing of the three-way regulating valve must be clear about which way to use, that is, the horizontal position or the vertical position. It has three channels, which can replace two through single seat regulating valves for the two groups of shunt and confluence and the occasions with temperature difference ≤ 150 ℃. When DN ≤ 80mm, confluence valve can be used for the occasions of shunt.
Diaphragm regulating valve
The diaphragm regulating valve is composed of a corrosion-resistant diaphragm and a valve body lined with a corrosion-resistant material. It has a simple flow path and is suitable for two-position cut-off occasions of unclean medium and weak corrosive medium. It is one of the earliest regulating valves. Due to its near quick opening flow characteristics, poor regulating quality and the influence of diaphragm and lining materials, it can not be used in high temperature and high pressure conditions. Generally, the working pressure is ≤ 1.6Mpa, and the working temperature is ≤ 150 ℃. In addition, the diaphragm is easy to be damaged and has short service life. Now, there are not many occasions for its use.
The butterfly valve is equivalent to a section of pipe to make the valve body, and the central valve plate is set for throttling. It is the most common rotary control valve used for control. It is suitable for low pressure, medium pressure or very few cases, but the pressure difference is limited. Its volume is small and its weight is light. It is 4-10 times lighter than the same caliber ball type regulating valve. Its caliber and price ratio is small. It is especially suitable for large caliber occasions. The larger the caliber of the regulating valve, the more remarkable this feature is. Generally, when DN > 300 mm, it is usually completed by butterfly valve.
Ball valve is a mature old product, which is divided into “O” and “V” ball valves. The flow path is the simplest, the flow resistance is the smallest, the loss is the smallest, and the “self-cleaning” performance is the best. “O” ball valve is a non resistance regulating valve. Compared with the specification, it has the largest rated flow coefficient, which is commonly used in the occasion of large flow and unclean media; “V” ball valve provides approximate logarithmic flow characteristics, and has large adjustable ratio. “V” ball core and valve seat produce shearing effect when rotating relative to each other, especially for the adjustment of unclean and fibrous media such as high viscosity, suspended flow, pulp, etc Section and cut. Ball valves are more expensive.
Eccentric rotary valve
It is also called cam flexure valve. It combines the advantages of ball valve and butterfly valve. It has simple flow path, good self-cleaning performance and adjustment performance, and is suitable for crystallization, stutter and unclean medium occasions. The valve body is small in volume and light in weight, and can be flexibly assembled according to the site installation position without replacing any parts. The rated flow coefficient is large, which is 10% – 30% larger than the single seat and double seat regulating valves of the same caliber, The adjustable ratio is large, up to 100:1; the valve seat is sealed reliably. Due to the disturbing effect of the support arm of the valve core and the eccentric rotation movement of the spherical surface of the valve core, the required operating torque is reduced, and some asymmetry is compensated, and the valve can operate stably under the conditions of flow opening, flow closing and high pressure difference; when the proportion is adjusted, a positioner is required, which can easily obtain a straight line or equal by changing the position of the convex plate in the positioner Percentage flow characteristics.
Selection of special regulating valve
For special application, on the basis of the above-mentioned regulating valve, if the upper valve cover is lengthened and heat sink is added, it can be used in low and high temperature occasions; the volume and weight of the whole regulating valve can be reduced by using the actuator with multiple springs; and a series of noise reduction measures can be used to reduce the noise to design a low-noise regulating valve. In addition, there are valve body separation regulating valve with valve body separation structure for maintenance and cleaning; fast cut-off regulating valve for fast interlocking action; small flow regulating valve designed for small flow control requirements; bellows seal regulating valve used to prevent leakage, etc.
These special types of control valves are designed to meet the requirements of special process production process or a specific use of special valves, which are non-standard. They have the characteristics of complex working conditions, high use requirements and small production batch. These control valves are usually evolved and improved from standard products according to the use requirements. Therefore, the basic type should be determined first according to the non particularity, and then the corresponding deformation type and material should be determined according to the particularity.
Selection of accessories
The accessories of the regulating valve mainly include: valve positioner, valve position switch, pneumatic holding valve, pneumatic relay, solenoid valve, air filter pressure reducer, hand wheel mechanism, valve position transmitter and converter, etc. Among them, the valve positioner includes electric valve positioner and pneumatic valve positioner, which are mainly used to improve the working characteristics of the regulating valve, realize correct positioning, improve the linearity of the position of the regulating valve, reduce the transmission lag of the regulating signal, change the flow characteristics of the regulating valve, change the response range of the regulating valve to the signal pressure, and realize the split control and correct positioning. It is one of the most important accessories of the regulating valve. Its quality will directly affect the performance and quality of the regulating valve and the regulating system. The following focuses on several main factors to be considered when selecting valve positioner:
- 1) Whether the valve positioner can realize the “split range” function, that is, the valve positioner only responds to a certain range of input signal. If the valve positioner can realize this function, two or more control valves can be controlled by one input signal according to the actual needs;
- 2) Whether the zero point and range are easy to adjust, whether the calibration is independent and how stable;
- 3) What is the accuracy of the valve positioner. Under the ideal working condition, the internal parts of the regulating valve (including the valve core, valve rod, valve seat, etc.) should be accurately positioned at the required position each time, regardless of the direction of travel or the load borne by the internal parts of the regulating valve;
- 4) What is the operating speed and frequency characteristics of the valve positioner. Because the valve positioner can constantly compare the input signal and valve position, and adjust its own output according to the deviation between them. If the valve positioner responds to the deviation quickly, the flow of medium in unit time will be large, and the response of the regulating system to the change of set point and load will be faster, that is to say, the smaller the system error is, the better the control quality will be. Generally speaking, the higher the frequency characteristic, that is, the higher the sensitivity to the frequency response, the better the control performance. It should be noted that the evaluation of frequency characteristics should be based on the combination of experiment and theory, rather than on theory. In the evaluation, the experimental method must be stable and scientific, and the valve positioner and actuator should be considered together;
- 5) After the combination of valve positioner and control valve, how does the positioning resolution change. The positioning resolution has a very obvious effect on the control quality of the regulating system, because the higher the resolution is, the closer the positioning of the regulating valve is to the ideal value, and the fluctuation caused by the over adjustment of the regulating valve can be effectively suppressed, so as to ultimately limit the periodic change of the regulated quantity.
- 6) Whether the maximum rated air supply pressure of the valve positioner matches the rated operating pressure of the actuator, whether the installation and connection are convenient, and how much maintenance and degree are, etc.
In addition to the valve positioner, other types of accessories are relatively simple and do not need to be repeated here. All accessories play the role of supplementary functions and ensuring the correct operation of the control valve. The principle to be grasped in the selection is necessary increase and unnecessary abandonment, otherwise it will only improve the operation cost of the control system and reduce the reliability.
Treatment method of the control valve stuck or blocked
For the installation of the control valve, including some problems that are easy to occur in the use process, for effective treatment, the valve will play a good control role in the control system. Especially for the valve often occurs stuck or blocked treatment.
The welding slag, rust and slag in the pipeline are blocked or stuck in the orifice, guide position and balance hole of lower valve cover, which causes the surface of valve core and guide surface to be pulled and scratched, and the sealing surface to be pressed. This often occurs at the beginning of new operation system and operation after overhaul. This is the most common failure. In this case, it is necessary to remove the slag for cleaning. If the sealing surface is damaged, it is also necessary to grind it. At the same time, open the bottom plug to flush out the slag falling into the lower valve cover from the balance hole and flush the pipeline. Before putting into operation, the regulating valve shall be fully opened, and the medium shall be put into normal operation after flowing for a period of time.
External scour method
When the ordinary valve is used to regulate the medium which is easy to precipitate and contains solid particles, it is often blocked at the throttle port and guide position, and the flushing gas and steam can be connected outside the bottom plug of the lower valve cover. When the valve is blocked or stuck, open the external gas or steam valve to complete the flushing work without moving the regulating valve, so that the valve can operate normally.
Installation of pipeline filter
For small caliber control valve, especially for ultra-small flow control valve, its throttling clearance is very small, and there should not be a little slag in the medium. In case of blockage, it is better to install a filter on the pipeline in front of the valve to ensure the smooth passage of media. The regulator valve with positioner works abnormally, and the most common failure is the blockage of its air throttle. Therefore, when working with positioner, the air source must be handled well. The usual method is to install air filter pressure reducing valve on the air source pipeline in front of the positioner
Increase the throttle clearance
For example, the solid particles in the medium or the welding slag and rust washed out in the pipeline can not pass through the orifice, resulting in blocking, jamming and other faults. The throttling parts with large throttling clearance can be used instead – the throttling area is the valve core and sleeve with windows and openings. Because the throttling area is concentrated rather than circular distribution, the faults can be easily eliminated. If it is a single seat valve or a double seat valve, the plunger shaped valve core can be changed into a V-shaped valve core or a sleeve valve. For example, a double seat valve is often stuck in a chemical plant. It is recommended to use sleeve valve instead, and the problem will be solved immediately.
Medium scouring method
The flushing energy of the medium itself is used to wash and take away the things that are easy to precipitate and block, so as to improve the anti blocking function of the valve. The common methods are:
- ① Changing to flow closed type;
- ② Adopting streamline valve body;
- ③ Putting the orifice at the place with the most severe scour, so we should pay attention to improving the erosion resistance of the throttle material.
Change straight to angle method
The direct flow is reverse s flow, the flow path is complex, and there are many dead zones in the upper and lower cavities, which provides a place for the deposition of media. Angle connection, medium as if flowing through 90 ℃ elbow, good scour performance, small dead zone, easy to design into flow line. Therefore, it can be changed to angle valve when the through regulating valve is slightly blocked.
Working principle of pneumatic control valve:
Pneumatic control valve is usually composed of pneumatic actuator and regulating valve connection, installation and commissioning. Pneumatic actuator can be divided into single acting actuator and double acting actuator. There is a return spring in the single acting actuator, but there is no return spring in the double acting actuator. The single acting actuator can automatically return to the opening or closing state initially set by the valve in case of air source loss or failure.
Principle of pneumatic control valve
According to the action form, pneumatic control valve can be divided into air open type and air close type, that is, the so-called normally open type and normally closed type. The air open or air close of pneumatic control valve is usually realized by the positive and negative action of actuator and different assembly methods of valve structure.
Action mode of pneumatic control valve
Air open type (normally closed type) is when the air pressure on the membrane head increases, the valve acts in the direction of increasing the opening, when the upper limit of the input air pressure is reached, the valve is in the fully open state. Conversely, when the air pressure decreases, the valve acts in the closing direction, and when there is no air input, the valve is fully closed. Usually, we call the air open type control valve a fault closed type valve.
The action direction of air close type (normally open type) is just opposite to that of air open type. When the air pressure increases, the valve acts in the closing direction; when the air pressure decreases or does not, the valve moves in the opening direction or fully open. Usually, we call the air closed regulating valve a fault open valve.
Structure characteristics and working principle of electric control valve
The electric control valve is mainly composed of the electric actuator and the valve body. By receiving the signals from the industrial automation control system, it drives the valve to change the cross-sectional area control between the valve core and the valve seat, and to control the flow, temperature, pressure and other process parameters of the pipeline medium, so as to realize the remote automatic control. It has the characteristics of stable regulation and good regulation performance.
Structure features of electric control valve:
- 1. The servo amplifier adopts deep dynamic negative feedback, which can improve the accuracy of automatic regulation.
- 2. There are many kinds of electric operators, which can be used for 4 ~ 20mA. DC or 0 ~ 10ma.dc.
- 3. The adjustable range is large, the inherent adjustable ratio is 50, and the flow characteristics are straight line and equal percentage.
- 4. Electronic electric control valve can directly control the valve opening by current signal without servo amplifier.
- 5. The valve body is designed according to the principle of hydrodynamics, and the rated flow coefficient is increased by 30%.
Structure classification of electric control valve:
The electric control valve can be generally divided into single seat and double seat structures. The electric single seat control valve is suitable for the working occasions with strict leakage requirements, low pressure difference between the front and back of the valve, certain viscosity and fiber medium. The electric double seat control valve has small imbalance force, large allowable pressure difference, large flow capacity waiting point, and is suitable for the occasions with less strict leakage requirements.
Working principle of electric control valve:
According to the signals of regulating parts, the electric regulating valve automatically controls the opening of the valve, so as to achieve the regulation of medium flow, pressure and liquid level. For the most commonly used 4-20mA current signal, when the control system gives 4mA signal to the electric control valve, the control valve is in the fully closed state, and when it gives 20mA signal, the control valve is in the fully closed state. Different signal values in the middle of 4-20mA correspond to different opening of regulating valve, that is, when the control system gives its 12mA signal, the opening of regulating valve is 50%. According to the selection of the suitable flow coefficient of the working medium, the flow and pressure corresponding to each opening of the regulating valve can be calculated. So as to meet the regulating requirements of the regulating valve for the working medium.
Working principle of self operated regulating valve
Self operated regulating valve, also known as self operated control valve, is a new type of regulating valve. As the name implies, it does not need external power supply and secondary instrument, and relies on the pressure and temperature of the medium flowing through the valve as the energy to drive the valve to work automatically. It uses the feedback signal (pressure, differential pressure and temperature) at the output end of the valve to transmit it to the actuator through the signal pipe, driving the valve flap to change The opening of the valve can adjust the pressure, flow and temperature.
According to the structure and function, the self operated regulating valve can be generally divided into: self operated temperature regulating valve, self operated pressure regulating valve, self operated flow regulating valve, etc., which can be applied to the automatic regulation of most fluid media. It can effectively convert the energy of the fluid medium into the driving force, so as to control the opening and closing of the valve.
When the medium fluid flows through the valve core and valve seat before the valve, it will be converted into the pressure behind the valve. Then through the pipeline input, the upper chamber acts on the top tray, at this time, the generated force will be opposite to the spring reaction force, etc. This determines the relative position of the valve core and seat, thus controlling the pressure behind the valve. When the pressure behind the valve increases, the force acting on the top plate also increases, making the valve core close to the position of the valve seat, so that the gap between the valve core and the valve seat will be reduced, and the pressure after the valve with large flow resistance will be reduced. Until the force on the top plate is balanced with the spring reaction force, so that the pressure behind the valve drops to the preset value. When the pressure behind the valve is reduced, the direction of action is the opposite of what was said before. This is the working process of the self operated regulating valve.
For the traditional control valve, the self-contained control valve does not need external energy, only relying on the output signal of the regulated medium, it can effectively regulate the properties of the fluid medium, which not only greatly saves the cost of some additional accessories, but also reduces the use of energy, meeting the call of national energy conservation and emission reduction.
Difference and selection of electric control valve and pneumatic control valve
The regulating valve is composed of actuator and valve. It can be divided into electric regulating valve, pneumatic regulating valve and self operated regulating valve. So as the most commonly used electric control valve and pneumatic control valve, how to distinguish and choose?
As the name implies, the biggest difference between the two is that one is to use power control, the other is to use gas source control! Electric control valve uses motor for power, while pneumatic control valve uses compressed air for power. Fundamentally speaking, there is not much difference, but the form of driving is different! The basic error and sensitivity of the electric control valve are up to 0.3%, so it is not necessary to establish another air source, and it is not suitable for the occasions with high explosion-proof requirements. The basic error and sensitivity of the pneumatic control valve are 0.5%. It is necessary to establish another gas source station, but it is intrinsically safe. It is suitable for the occasion with high explosion-proof requirements.
Selection of electric control valve and pneumatic control valve:
- 1. From the price point of view: the price of pneumatic control valve will be more economical than that of electric control valve. Only the gas source is needed for power!
- 2. From application: pneumatic control valve needs to be equipped with compressor and other equipment, the advantage is that it has explosion-proof function, simple maintenance and low failure rate, so in chemical, petrochemical and other industries, the range of use is far greater than electric control valve.
- 3. From the operation time: the action of pneumatic control valve is relatively faster, but it needs stable air source, and the electric control valve will be slower!
- 4. The electric control valve has high control accuracy, can be used with electricity, and can be equipped with a variety of related functions;
- 5. The accuracy of pneumatic control valve is low, it needs air supply equipment and signal conversion accessories.
- 6. Electric control valve is mainly used in power plant or nuclear power plant, because it needs a smooth, stable and slow process in high-pressure water system.
Advantages and disadvantages of electric control valve and pneumatic control valve:
- (1) Advantages of electric control valve: good effect on liquid medium and large diameter gas, not affected by climate. Not affected by air pressure. Disadvantages: high cost, bad in humid environment.
- (2) Advantages of pneumatic control valve: good effect on gas medium and small diameter liquid, low cost and convenient maintenance. Disadvantages: affected by the pressure fluctuation of air compressor, it is easy to be affected by the water content of air compressor in winter in the north, resulting in freezing and inaction of transmission part.
The difference between the two is one power and one gas. In terms of selection, the user should consider selecting the appropriate valve type according to the installation position, whether there is gas source or power supply, switch speed requirements, etc.
Difference between pneumatic control valve and self operated control valve
Self operated regulating valve can not only control the pressure behind the valve, but also control the pressure in front of the valve. The self operated regulating valve is actually a pure proportional regulating system, and there will be surplus. The regulating valve controls the pressure regardless of the flow. But for any kind of regulating valve, the direct control is the flow. The biggest difference between these two types of valves lies in that the control valve not only needs external energy (such as power supply or air source) as driving energy, but also needs to receive external control instrument signals to change the relative position of the closure parts in the valve, so as to change the fluid flow. The self operated regulating valve does not need external energy, and does not need to receive external control instrument signals. Only the pressure signal of the regulated medium can realize the pressure regulation. The feature of the self operated pressure regulating valve is that the operation force of the product is small because the self operated pressure regulating valve has no external driving energy.
Regulation: the regulation accuracy of the regulating valve is higher than that of the self operated valve
The regulating accuracy of the self operated regulating valve is basically determined by the spring and diaphragm accuracy of the self operated valve. Generally, the final regulating accuracy is not better than 5%, and 10% is guaranteed.
However, the final adjustment accuracy of ordinary control valve depends on the accuracy of the meter feeder and the regulator, while the regulator has a high accuracy and its impact is generally ignored.
Therefore, the regulating accuracy of the self operated valve must be much worse than that of the ordinary regulating circuit. When the regulating accuracy is high, it is not recommended to use the self operated valve.
Generally speaking, the effect of regulating valve and self operated regulating valve used to regulate the pressure is no different, but the regulating valve is the balance of instrument air, spring force and medium, and the self operated valve is the balance of capsule medium pressure, spring and pipeline medium pressure. If the upstream pressure changes, the opening of the self operated valve will change, and the flow will change accordingly.
Application: one field, one remote transmission, one medium pressure regulation, one instrument air.
If the regulating valve is led to DCS control, it can easily change the given value, can be closed or opened manually and quickly, and can have various related trend records.
The self regulating valve can not be adjusted basically, and can only be operated on site. The degree of intelligence should be greatly reduced. The self operated regulating valve is troublesome to adjust the setting value, so it is used in the situation where the setting does not need to be changed frequently, such as equipment lubricating oil supply, etc. The self operated regulating valve needs to take pressure from the process medium, so it is not suitable for cleaner occasions when the medium has corrosion, particles, etc.
Installation and Design:
The self operated regulating valve has pressure taking control in front of the valve and pressure taking control in back of the valve. During the design, a good space shall be reserved for the installation of pressure points. During installation, the executive structure of the self operated regulating valve on the steam pipeline shall be installed downward, and the pressure tapping point shall be connected to the condenser from the bottom of the main pipe. The condenser shall be higher than the executive mechanism and lower than the main steam pipe, so as to avoid the steam overheating damaging the valve body. In addition, the actuator shall be installed upward. Since self operated regulating valve is often used for gas pipe, the pressure tapping point shall be opened from the top of the main pipe.
The correct selection of the regulating valve is the first and the most critical step in the application of the regulating valve. The selection directly affects the use effect of the regulating valve, and then affects the regulating quality of the system. Of course, the selection work is more complex, but also a knowledge, which needs to be explored and summarized in practical application. Therefore, it is necessary for us to master certain methods and skills in the selection of regulating valve and on the premise of being familiar with relevant professional knowledge. Only in this way can we truly play the role of “hands and feet” in industrial process automation control
Source: china control valve supplier: www.epowermetals.com
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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