What is a butterfly valve?
What is a butterfly valve?
Table of Contents
- 1 What is a butterfly valve?
- 2 Butterfly valve parts:
- 3 Working principle of butterfly valve:
- 4 Classification of butterfly valves:
- 5 Features of butterfly valve:
- 6 Application of butterfly valve:
- 7 How to choose butterfly valves?
- 8 Installation and maintenance of butterfly valve:
- 9 Common faults of butterfly valve and elimination methods:
- 10 Butterfly valve vs gate valve:
- 11 Butterfly valve vs ball valve
- 12 What is butterfly valve used for?
- 13 How does a butterfly valve work?
- 14 Which valve is best for flow control?
- 15 Why is it called a butterfly valve?
Butterfly valve, also known as flap valve, is a simple control valve, which can also be used for the on-off control of low-pressure pipeline medium. Butterfly valve refers to a kind of valve whose closing piece (disc or disc) is a disc and revolves around the valve axis to open and close. It mainly cuts off and throttles the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so as to achieve the purpose of opening and closing or adjustment. The butterfly valve is applicable to the pipelines conveying various corrosive and non corrosive fluid media in the engineering systems of generator, gas, natural gas, liquefied petroleum gas, urban gas, hot and cold air, chemical smelting, power generation and environmental protection, etc., and is used to regulate and cut off the flow of media.
Butterfly valves are mainly composed of valve body, valve rod, butterfly plate and sealing ring. The valve body is cylindrical with short axial length and built-in butterfly plate.
Butterfly valve is a kind of valve which uses the circular butterfly plate as the opening and closing parts and turns with the valve stem to open, close and adjust the fluid channel. The butterfly plate of butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of butterfly valve body, the disc butterfly plate rotates around the axis with the rotation angle between 0 ° and 90 °. When the rotation angle reaches 90 °, the valve will be fully open, and the deflection angle of the disc plate can be controlled by changing it Flow rate of medium.
I. By driving mode
- 1. Electric butterfly valve
- 2. Pneumatic butterfly valve
- 3. Hydraulic butterfly valve
- 4. Manual butterfly valve
II. According to the structure:
- 1. Central sealing butterfly valve
- 2. Single eccentric sealing butterfly valve
- 3. Double eccentric sealing butterfly valve
- 4. Three eccentric sealing butterfly valve
III. Sealing surface materials:
1. Soft seal butterfly valve:
- ① the sealing pair is composed of non-metallic soft material and non-metallic soft material;
- ② the sealing pair is composed of metal hard material and non-metal soft material.
2. Metal hard seal butterfly valve. The sealing pair is composed of metal hard material and metal hard material.
IV. According to the sealing form:
1. Forced sealing butterfly valve:
- ① elastic sealing butterfly valve: the sealing specific pressure is generated by the elasticity of the valve seat or valve plate when the valve plate presses the valve seat when the valve is closed;
- ② external torque sealing butterfly valve: the sealing specific pressure is generated by the torque applied on the valve shaft.
2. Pressure filled sealed butterfly valve: the specific pressure of the seal is generated by the pressure of the sealing element of the valve seat or valve plate.
3. Automatic sealing butterfly valve: the sealing specific pressure is automatically generated by the medium pressure.
V. According to working pressure:
- 1. Vacuum butterfly valve: the working pressure is lower than the atmospheric pressure of the standard reactor;
- 2. Low pressure butterfly valve: butterfly valve with nominal pressure PN < 1.6Mpa;
- 3. Medium pressure butterfly valve: butterfly valve with nominal pressure PN of 2.5-6.4mpa;
- 4. High pressure butterfly valve: nominal pressure PN is 10. 0-80.0mpa butterfly valve;
- 5. Ultra high pressure butterfly valve: butterfly valve with nominal pressure PN > 100MPa.
Vi. According to the working temperature:
- 1. High temperature: T > 450 ° C butterfly valve;
- 2. Medium temperature butterfly valve: 120 C < T < 450 ℃;
- 3. Normal temperature butterfly valve: a butterfly valve with 40C < T < 120 ° C;
- 4. Low temperature butterfly valve: a 100 < T < 40 ° C butterfly valve;
- 5. Ultra low temperature butterfly valve: T < 100 ° C.
VII. According to the connection mode:
1. Wafer butterfly valve
- The butterfly plate of wafer butterfly valve is installed in the diameter direction of the pipeline. The valve is fully open.
- The wafer butterfly valve is simple in structure, small in volume and light in weight. Butterfly valve has two types of seals: elastic seal and metal seal. Elastic sealing valve, sealing ring can be inlaid on the valve body or attached to the periphery of butterfly plate.
The wafer style butterfly valve is designed to maintain a seal against bi-directional pressure differential to prevent any backflow in systems designed for unidirectional flow. It accomplishes this with a tightly fitting seal; i.e., gasket, o-ring, precision machined, and a flat valve face on the upstream and downstream sides of the valve.
2. Flange type butterfly valve
The flange type butterfly valve is of vertical plate structure, and the valve stem is the sealing ring of integral metal hard sealing valve; it is of composite structure of flexible graphite plate and stainless steel plate, which is installed on the valve body, and the sealing surface of butterfly plate is overlaid with stainless steel. The sealing ring of the soft sealing valve is made of nitrile rubber and is installed on the butterfly plate.
3. Lug type butterfly valve
4. Welded butterfly valve
Welded butterfly valve is a kind of non airtight butterfly valve, which is widely used in the production process of building materials, metallurgy, mining, electric power, etc. the medium temperature is ≤ 300 ℃ and the nominal pressure is 0.1MPa. It is used to connect, open and close or adjust the medium quality.
- 1. The butterfly valve has the characteristics of simple structure, small volume, light weight, low material consumption, small installation size, quick switch, 90 ° reciprocating rotation, small driving torque, etc. it is used to cut off, connect and regulate the medium in the pipeline, and has good fluid control characteristics and closing sealing performance;
- 2. The butterfly valve can transport mud with the least liquid accumulated at the pipe mouth; under low pressure, it can achieve good sealing and regulation performance;
- 3. The streamlined design of butterfly plate makes the loss of fluid resistance small, which can be described as an energy-saving product;
- 4. The valve rod is of through rod structure, which has good comprehensive mechanical properties, corrosion resistance and scratch resistance after tempering treatment. When the butterfly valve is opened and closed, the valve rod only rotates without lifting, the packing of the valve rod is not easy to be damaged, and the sealing is reliable. It is fixed with the taper pin of the butterfly plate, and the extension end is designed to prevent the valve rod from bursting out when the valve rod is accidentally broken at the connection of the valve rod and the butterfly plate;
- 5. The connection mode includes flange connection, clamp connection, butt welding connection and lug clamp connection.
- The driving mode includes manual, worm gear drive, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators, which can realize remote control and automatic operation.
- 1. It is convenient to open and close, labor-saving, low fluid resistance, and can be operated frequently;
- 2. Simple structure, small size, short length, small volume and light weight, suitable for large caliber valves;
- 3. The mud can be transported, and the minimum liquid can be accumulated at the pipe mouth;
- 4. Under low pressure, good sealing can be achieved;
- 5. Good regulation performance;
- 6. When the valve is fully opened, the effective flow area of the valve seat channel is large and the fluid resistance is small;
- 7. The opening and closing torque is small, because the disc on both sides of the shaft is basically the same under the action of the medium, and the direction of the torque is opposite, so the opening and closing is relatively labor-saving;
- 8. The sealing surface material is generally rubber and plastic, so the low-pressure sealing performance is good;
- 9. Convenient installation;
- 10. Flexible and labor-saving operation, manual, electric, pneumatic and hydraulic modes can be selected.
- 1. The range of working pressure and temperature is small.
- 2. Poor sealing.
Butterfly valve can be divided into offset plate, vertical plate, inclined plate and lever type according to its structure.
According to the sealing form, there are two types: soft sealing type and hard sealing type. Rubber ring seal is generally used for soft seal type and metal ring seal is generally used for hard seal type.
According to the connection type, it can be divided into flange connection and wafer connection; according to the transmission mode, it can be divided into manual, gear transmission, pneumatic, hydraulic and electric.
- 1. Butterfly valve is suitable for flow regulation. Because the pressure loss of butterfly valve in the pipeline is relatively large, about three times of that of gate valve, the influence of pressure loss on the pipeline system should be fully considered when selecting butterfly valve, and the firmness of the butterfly plate bearing the pipeline medium pressure when closing should also be considered. In addition, it is necessary to consider the working temperature limit of elastic seat material under high temperature. The structure length and overall height of butterfly valve are small, opening and closing speed is fast, and it has good fluid control characteristics. The structure principle of butterfly valve is most suitable for making large-diameter valve. When the butterfly valve is required to control the flow, the most important thing is to select the size and type of the butterfly valve correctly, so that it can work properly and effectively.
- 2. Generally, in throttling, regulating control and mud medium, short structure length and fast opening and closing speed (1/4 revolution) are required. Low pressure cut-off (small differential pressure), butterfly valve is recommended.
- 3. Butterfly valve can be selected when there are two position adjustment, contraction ground channel, low noise, cavitation and gasification, a small amount of leakage to the atmosphere and abrasive medium.
- 4. In case of throttling regulation under special working conditions, or strict sealing requirements, or severe wear, low temperature (deep cold) and other working conditions, special butterfly valve with three eccentric or double eccentric of special design metal sealing belt regulating device shall be used.
- 5. The middle line butterfly valve is suitable for fresh water, sewage, sea water, salt water, steam, natural gas, food, medicine, oil products, various acid and alkali and other pipelines with the requirements of complete sealing, zero leakage in gas test, high service life and operating temperature of – 10 ~ 150 ℃
- 6. The soft sealing eccentric butterfly valve is suitable for the bidirectional opening and closing and adjustment of the ventilation and dust removal pipeline, and is widely used in the gas pipeline and water channel of metallurgy, light industry, electric power, petrochemical system, etc.
- 7. Metal to metal sealed double eccentric butterfly valve is applicable to gas, oil, acid and alkali pipelines such as urban heating, gas supply, water supply, etc. as regulating and throttling devices.
- 8. Metal to metal face sealing three eccentric butterfly valve is not only used as program control valve of large PSA gas separation device, but also widely used in petroleum, petrochemical, chemical, metallurgy, electric power and other fields. It is a good substitute for gate valve and stop valve.
- 1. Because the pressure loss of the butterfly valve is relatively large compared with the gate valve, it is suitable for the pipeline system with lax pressure loss requirements
- 2. Since the butterfly valve can be adjusted by flow, it is suitable for selection in the pipeline requiring flow adjustment
- 3. Due to the limitation of butterfly valve structure and sealing material, it is not suitable for high temperature and high pressure pipeline system. Generally, the working temperature is below 300 ℃, and the nominal pressure is below PN40.
- 4. Because the structural length of butterfly valve is relatively short, and it can be made into large diameter, so in the case of short structural length or large diameter valve (such as more than DN1000), butterfly valve should be selected.
- 5. Since the butterfly valve can be opened or closed only by rotating 90 °, it is suitable to select the butterfly valve in the field with fast opening and closing requirements.
The butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. The butterfly valve is simple in structure, small in volume and light in weight. It is only composed of a few parts, and can be opened and closed quickly only by rotating 90 °. The operation is simple. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the butterfly plate thickness is the resistance when the medium flows through the valve body, so the pressure drop generated through the valve is very small, so it has better flow control characteristics.
If butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of valve. The structure and principle of butterfly valve is especially suitable for making large-diameter valve. There are two kinds of butterfly valves commonly used: wafer butterfly valve and flange butterfly valve. Double clip butterfly valve is to connect the valve between two pipe flanges with stud bolts. Flange butterfly valve is to connect the flange on both ends of the valve to the pipe flange with bolts.
Butterfly valve, as a component used to realize on-off and flow control of pipeline system, has been widely used in many fields, such as petroleum, chemical industry, metallurgy, hydropower, etc. In the well-known butterfly valve technology, the sealing structure is mostly adopted, and the sealing materials are rubber, polytetrafluoroethylene, etc. Due to the limitation of structural features, it is not suitable for industries such as high temperature, high pressure, corrosion resistance and wear resistance.
A more advanced butterfly valve is a three eccentric metal hard seal butterfly valve. The valve body and valve seat are connected components. The sealing surface of valve seat is overlaid with heat-resistant and corrosion-resistant alloy materials. The multi-layer soft laminated seal ring is fixed on the valve plate. Compared with the traditional butterfly valve, this butterfly valve has the advantages of high temperature resistance, light operation, no friction between opening and closing. When closing, it compensates the seal with the increase of the torque of the transmission mechanism, improving the sealing performance of the butterfly valve and prolonging its service life.
However, the following problems still exist in the use of this butterfly valve:
- 1. Because the multilayer soft and hard laminated seal ring is fixed on the valve plate, when the valve plate is normally open, the medium will form a positive flushing on its sealing surface, and the soft sealing belt in the metal sandwich will directly affect the sealing performance after being washed.
- 2. Limited by the structural conditions, the structure is not suitable for valves with a diameter below DN200, because the overall structure of the valve plate is too thick and the flow resistance is large.
- 3. Due to the principle of three eccentric structure, the sealing between the sealing surface of the valve plate and the valve seat depends on the torque of the transmission device to make the valve plate press against the valve seat. In the positive flow state, the higher the medium pressure, the tighter the sealing extrusion. When the medium flow reverses, with the increase of the medium pressure, the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, and the seal begins to leak.
The high-performance three eccentric two-way hard sealing butterfly valve is characterized in that the valve seat sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shaped sealing ring. The sealing surface of valve plate and valve seat is of inclined cone structure, and the temperature resistant and corrosion-resistant alloy material is overlaid on the inclined cone surface of valve plate; the spring fixed between the pressure plate of regulating ring is assembled with the regulating bolt on the pressure plate.
This structure effectively compensates the tolerance zone between the shaft sleeve and the valve body and the elastic deformation of the valve stem under the medium pressure, and solves the sealing problem of the valve in the process of two-way exchange medium transportation. The sealing ring is composed of two layers of stainless steel plates on both sides of soft T-shape, which has the double advantages of metal hard sealing and soft sealing. It has the sealing performance of zero leakage no matter at low or high temperature.
The test shows that the pressure of sealing surface is caused by the moment of transmission device and the effect of medium pressure on valve plate when the flow direction of medium is the same as the rotation direction of butterfly plate. When the positive medium pressure increases, the closer the oblique conical surface of the valve plate and the sealing surface of the valve seat are squeezed, the better the sealing effect is. When the reverse flow state, the seal between the valve plate and the valve seat relies on the torque of the driving device to make the valve plate press against the valve seat. With the increase of the reverse medium pressure, when the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, the deformation stored by the spring of the regulating ring after being loaded can compensate the tight pressure between the valve plate and the valve seat sealing surface automatically. Therefore, unlike the prior art, the utility model is directly installed on the valve body instead of installing the soft and hard multi-layer sealing ring on the valve plate, and adding an adjusting ring between the pressing plate and the valve seat is a very ideal two-way hard sealing method. It will replace gate, globe and globe valves.
The butterfly valve is simple in structure, small in volume, light in weight, and has few components. It can be made up of several key parts. It is also very convenient to open. It only needs to select the switch to 90 degrees. The butterfly valve has a very good control over the fluid, which can increase or reduce the flow at any time. The valve has certain resistance when transporting any fluid The resistance of butterfly valve mainly comes from itself, such as the thickness of butterfly valve body. If you want to reduce the resistance to the fluid, you only need to reduce its thickness.
The elastic seal has the limitation of temperature.
Butterfly valve is also widely used. If it is used to control the flow, it needs to choose different types and valve body sizes, because the butterfly valve itself is more suitable for some larger caliber valves when it is designed. Butterfly valve is not only widely used in petroleum, gas, chemical industry, water treatment and other general industries, but also in the cooling water system of thermal power station.
- 1. During installation, the disc shall be stopped at the closed position.
- 2. The opening position shall be determined according to the rotation angle of butterfly plate.
- 3. For butterfly valve with bypass valve, the bypass valve shall be opened before opening.
- 4. It shall be installed according to the installation instructions of the manufacturer. For heavy butterfly valve, a firm foundation shall be set.
Common faults of butterfly valve and elimination methods:
I. Butterfly valve failure: leakage of sealing surface
- 1. There are sundries in butterfly plate and sealing ring of butterfly valve;
- 2. The butterfly plate and sealing closed position of butterfly valve are not in good agreement;
- 3. The outlet is equipped with flange bolts with uneven stress or not compressed;
- 4. The pressure test direction is not as required.
- 1. Eliminate impurities and clean the inner chamber of the valve;
- 2. Adjust the limit screw of the actuator such as worm gear or electric actuator to reach the correct closing position of the valve;
- 3. Check the flange plane and bolt pressing force, and press evenly;
- 4. Spin in the direction of the arrow.
II. Butterfly valve failure: leakage at both ends of the valve
- 1. Sealing gasket on both sides is invalid;
- 2. The pressing force of the pipe flange is uneven or not pressed.
Butterfly valve vs gate valve:
Ⅰ. Distinguish from the definition:
- 1. Gate valve is one of the most common opening and closing valves. The gate (i.e. the opening and closing parts in the gate are called the gate or gate, and the gate seat is called the gate seat) is used to connect (fully open) or block (fully closed) the medium in the pipeline. It is not allowed to be used as closure. It should be avoided to open the ram slightly in use, because the erosion of high-speed flow medium will accelerate the damage of sealing surface. The one side of the gate, which is perpendicular to the center line of the gate seat channel, acts as the lifting movement and cuts off the medium in the pipeline like the gate, so it is called gate valve.
- 2. Butterfly valve refers to a kind of valve whose closing part (disc or disc) is a disc and revolves around the valve axis to open and close. It is mainly used for cutting off and throttling on the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so as to achieve the purpose of opening and closing or adjustment. Butterfly valve is generally less than 90 ° from full open to full close. Butterfly valve and butterfly rod have no self-locking ability. In order to locate butterfly plate, worm gear reducer shall be installed on the valve rod. The worm gear reducer can not only make the butterfly plate have self-locking ability, stop the butterfly plate at any position, but also improve the operation performance of the valve.
Ⅱ. From the aspect of action mode:
- 1. The gate valve belongs to the straight stroke valve, that is, the valve stem drives the valve plate to move vertically up and down to complete the opening and closing of the gate valve, so the flow resistance of the gate valve is small, but because of its high opening height, the opening and closing speed is slow.
- 2. Butterfly valve belongs to angle stroke valve, that is, the valve plate of butterfly valve rotates 90 ° around the valve axis to complete the opening and closing action of butterfly valve. Therefore, the opening height of butterfly valve is only one quarter of the channel diameter, so it can be opened and closed quickly.
III. according to the function and use of gate valve and butterfly valve:
- 1. The gate valve has small flow resistance and good sealing performance. Because the flow direction of the gate valve plate and the medium is vertical angle, if the gate valve is not opened and closed in place on the valve plate, the flushing of the medium on the valve plate will make the valve plate vibrate and easily damage the gate valve seal. Therefore, it is often used to cut off pipelines that require strict sealing and do not need frequent opening and closing, and is not suitable for regulating the medium parameters of pipelines Because of the slow speed of opening and closing, it is not suitable for the occasion of emergency cut-off. Gate valve has a wide range of working conditions, which can be used in high temperature, low temperature, high pressure, low pressure and other working conditions.
- 2. Butterfly valve not only has the function of cut-off, but also has the function of adjustment. The butterfly valve can be opened and closed quickly and frequently, which is especially suitable for the occasion requiring quick opening or cutting off. Compared with the gate valve, the butterfly valve has the advantages of small size, light weight and low price. In some cases where the installation space is limited, the wafer type butterfly valve can be selected to save more space.
Butterfly valve vs ball valve
The difference between the ball valve and the butterfly valve is that its opening and closing parts are block plates, while the ball valve is a ball. They all rotate around their own axis. Let’s continue to see the difference between butterfly valve and ball valve.
The cut-off method of ball valve and butterfly valve is different: the ball valve blocks the passage through the ball to realize the pipe cut-off flow; the butterfly valve relies on the butterfly wing, so the pipe will not flow if it is spread and sealed.
The structure of the ball valve is different from that of the butterfly valve: the ball valve is composed of the valve body, valve core and valve rod assembly, and the body can only see some parts; the butterfly valve is composed of the valve body, valve seat, valve plate and valve rod, and all the accessories are exposed outside. Therefore, the tightness of butterfly valve is not as good as that of ball valve. When it comes to sealing, butterfly valves are also divided into soft sealing and hard sealing. Butterfly valve structure is relatively simple, can only be used in low-pressure environment, the highest pressure is only 64 kg. Compared with the ball valve, the maximum ball valve can reach about 100 kg.
The working principle of the ball valve and butterfly valve is different: the ball valve has a 90 degree rotation action, only because its opening and closing parts are a ball, only need to operate 90 degree rotation to achieve opening or closing, which is most suitable for switching. But now v-ball valve can be used to regulate or control the flow. Butterfly valve is a kind of valve that uses disc type opening and closing parts to turn back and forth about 90 ° to open, close or regulate medium flow. It has a good function of regulating flow and is one of the fastest-growing valve varieties
Comparison between butterfly valve and ball valve
- Advantages of butterfly valve 1: simple structure, small volume and light weight; disadvantages are that the range of using pressure and working temperature is much smaller than that of ball valve.
- Advantages of butterfly valve 2: good sealing can be realized under low pressure; the disadvantage is that the sealing performance is much worse than that of ball valve.
- Advantages of butterfly valve 3: it can transport mud, with the least liquid accumulated in the pipe mouth, which is better than the ball valve
- Advantages of butterfly valve 4: the structural principle of butterfly valve is more suitable for making large-diameter valve, widely used in oil, gas, chemical industry and other industries.
Source: Best china butterfly valve supplier: www.epowermetals.com
What is butterfly valve used for?
A Butterfly valve is a quarter-turn rotational motion valve, that is used to stop, regulate, and start flow. A butterfly valve has a disc which is mounted on a rotating shaft. When the butterfly valve is fully closed, the disk completely blocks the line.
How does a butterfly valve work?
The “butterfly” is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid.
Why is it called a butterfly valve?
When the valve is closed, the disc is turned so that it completely blocks off the passageway. The butterfly valve derives its name from the way a “butterfly-shape image” appears to form as it turns. The butterfly valve is widely used in the chemical industry, wastewater systems and water supplies.