Comprehensive of butterfly valves

Butterfly valve is also called flap valve, is a simple structure of the control valve, can be used for the switch control of low-pressure pipeline media butterfly valve refers to the closing part (valve disc or butterfly plate) for the disc, revolving around the valve shaft to achieve the opening and closing of a valve.

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Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. It mainly plays the role of cutting and throttling on the pipeline. The opening and closing part of the butterfly valve is a disc-shaped butterfly plate that rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjusting.

Working principle

The butterfly valve is a kind of valve that is used to open, close or adjust the flow rate of the medium by rotating the disc type opening and closing part about 90°. The butterfly valve is not only simple in structure, small in size, light in weight, saving in material consumption, small in installation size, small in driving torque, simple and rapid in operation, but also has good flow regulation function and closing sealing characteristics, which is one of the fastest developing valve varieties in recent decades. Butterfly valves are widely used. The variety and number of its use continue to expand, and to high temperature, high pressure, large caliber, high sealing, long life, excellent regulating characteristics, as well as a valve multi-function development. Its reliability and other performance indicators have reached a high level.

With the application of chemically resistant synthetic rubber on the butterfly valve, the performance of the butterfly valve has been improved. Since synthetic rubber has the characteristics of corrosion resistance, erosion resistance, dimensional stability, good resilience, easy to form, low cost, etc., synthetic rubber with different properties can be selected according to different use requirements to meet the working conditions of the butterfly valve.

Because polytetrafluoroethylene (PTFE) has strong corrosion resistance, stable performance, not easy to age, low friction coefficient, easy to form, dimensional stability, and can improve its comprehensive performance by filling, adding appropriate materials, get better strength, lower friction coefficient of butterfly valve sealing material, overcome the limitations of synthetic rubber, Therefore, the polymer polymer material represented by polytetrafluoroethylene and its filling modified material have been widely used in the butterfly valve, so that the performance of the butterfly valve has been further improved, and the temperature and pressure range are wider, the sealing performance is reliable, and the service life of the butterfly valve is longer.

In order to meet the requirements of high and low temperature, strong erosion, long life and other industrial applications, metal sealed butterfly valves have been greatly developed. With the application of high temperature resistance, low temperature resistance, strong corrosion resistance, strong erosion resistance, high strength alloy materials in the butterfly valve, the metal sealed butterfly valve has been widely used in high and low temperature, strong erosion, long life and other industrial fields, and a large diameter (9~750mm), high pressure (42.0MPa), wide temperature range (-196~606℃) butterfly valve has appeared. So that the butterfly valve technology to reach a new level.

The butterfly valve has a small flow resistance when fully opened. When opened between about 15°~70°, sensitive flow control can be carried out, so in the field of large diameter adjustment, the application of butterfly valves is very common.

Due to the wipeability of the butterfly plate movement, most butterfly valves can be used in media with suspended solid particles. Depending on the strength of the seal, it can also be used for powder and granular media.

Butterfly valves are suitable for flow regulation. Because the pressure loss of the butterfly valve in the pipe is relatively large, about three times that of the gate valve, the influence of the pipeline system by the pressure loss should be fully considered when selecting the butterfly valve, and the strength of the butterfly plate under the pipeline medium pressure should also be considered when it is closed. In addition, the operating temperature limitations of the elastic seat material at high temperatures must be considered.

The structure length and overall height of the butterfly valve are small, the opening and closing speed is fast, and it has good fluid control characteristics. The structure principle of butterfly valve is most suitable for the production of large diameter valves. When butterfly valves are required to be used for flow control, the most important thing is to correctly select the specifications and types of butterfly valves so that they can work properly and effectively.

Generally, in the throttling, adjustment control and mud medium, the structure length is short, the opening and closing speed is fast, and the low pressure cutoff (small pressure difference) is recommended. In the two-position adjustment, reduced channel, low noise, cavitation and vaporization phenomenon, a small amount of leakage to the atmosphere, with abrasive media, butterfly valves can be selected. Throttle adjustment under special working conditions, or under conditions requiring strict sealing, severe wear, and low temperature (cryogenic).

structure

It is mainly composed of valve body, valve stem, butterfly plate and sealing ring. The valve body is cylindrical, the axial length is short, and the built-in butterfly plate.

peculiarity

1, the butterfly valve has a simple structure, small size, light weight, material consumption, small installation size, quick switch, 90° reciprocating rotation, small driving torque and other characteristics, used to cut off, connect, adjust the medium in the pipeline, with good fluid control characteristics and close sealing performance.

2, the butterfly valve can transport mud, the least liquid accumulated in the pipe mouth. At low pressure, good sealing can be achieved. Good adjustment performance.

3, the streamlined design of the butterfly plate, so that the fluid resistance loss is small, can be described as an energy-saving product.

4, the valve stem is a through rod structure, after tempering treatment, has good comprehensive mechanical properties and corrosion resistance, abrasion resistance. When the butterfly valve is opened and closed, the valve stem only rotates without lifting and lifting operation, and the packing of the valve stem is not easy to damage and the seal is reliable. It is fixed with the taper pin of the butterfly plate, and the overhang end is designed to prevent the valve stem from breaking out when the connection between the valve stem and the butterfly plate is accidentally broken.

5, the connection mode is flange connection, clamp connection, butt welding connection and lug clamp connection.

The driving forms are manual, worm gear transmission, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators, which can realize remote control and automatic operation.

advantage

1, easy to open and close, labor-saving, fluid resistance is small, can be often operated.

2, simple structure, small size, short structure length, small volume, light weight, suitable for large diameter valves.

3, can transport mud, the least liquid in the pipe mouth.

4, low pressure, can achieve a good seal.

5, good adjustment performance.

6. When 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 butterfly plate on both sides of the rotating shaft is basically equal to the effect of the medium, and the direction of the torque is opposite, so the opening and closing is less labor.

8, sealing surface material is generally used rubber, plastic, so the low pressure sealing performance is good.

9, easy to install.

10, the operation is flexible and labor-saving, manual, electric, pneumatic, hydraulic mode can be selected.

shortcoming

1, the use of pressure and working temperature range is small.

2, poor sealing.

According to the structure of the butterfly valve can be divided into offset plate, vertical plate, inclined plate and lever type.

According to the sealing form can be soft seal type and hard seal type two. The soft seal type is generally sealed by rubber ring, and the hard seal type is usually sealed by metal ring.

According to the connection type can be divided into flange connection and sandwich connection; According to the transmission mode can be divided into manual, gear transmission, pneumatic, hydraulic and electric several.

Main classification

According to the driving method

(1) Electric butterfly valve

(2) pneumatic butterfly valve

(3) hydraulic butterfly valve

(4) Manual butterfly valve

Divided by structural form:

(1) Center seal butterfly valve

(2) Single eccentric seal butterfly valve

(3) Double eccentric seal butterfly valve

(4) Three eccentric sealing butterfly valve

Sealing surface material:

(1) Soft seal butterfly valve.

1) The sealing pair is composed of a non-metallic soft material to a 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 to metal hard material.

According to the sealing form:

(1) Forced sealing of butterfly valve.

1) Elastic seal butterfly valve: the specific seal pressure is generated by the valve plate squeezing the valve seat when the valve is closed, and the elasticity of the valve seat or valve plate.

2) External torque seal butterfly valve: the specific pressure of the seal is generated by the torque applied to the valve shaft.

(2) Pressurized sealing butterfly valve: The specific sealing pressure is generated by the pressurized sealing element of the cartridge on the seat or valve plate.

(3) Automatic sealing butterfly valve: the sealing pressure is automatically generated by the medium pressure.

By working pressure:

(1) Vacuum butterfly valve. Butterfly valves with operating pressure lower than standard reactor atmospheric pressure.

(2) Low pressure butterfly valve. Nominal pressure 1.6 MPa butterfly valve.

(3) Medium pressure butterfly valve. The nominal pressure PN is 2.5-6.4mpa butterfly valve.

(4) High pressure butterfly valve. The nominal pressure PN is 10.0-80.0mpa butterfly valve.

(5) Super high pressure butterfly valve. Nominal pressure PN> 100MPa butterfly valve.

According to the operating temperature:

(1) High temperature. t> 450 °C butterfly valve.

(2) Medium temperature butterfly valve. 120 C< t< 450 ℃ butterfly valve.

(3) Normal temperature butterfly valve. One forty t< 120 °C butterfly valve.

(4) Low temperature butterfly valve. A hundred t< A 40 °C butterfly valve.

(5) ultra-low temperature butterfly valve. t< A 100 °C butterfly valve.

By connection type:

1, clamp butterfly valve

The butterfly plate of the clamping butterfly valve is installed in the diameter direction of the pipe. The valve is fully open.

The butterfly valve is simple in structure, small in size and light in weight. Butterfly valves have two seal types: elastic seal and metal seal. Elastomeric sealing valve, the sealing ring can be mounted on the valve body or attached to the periphery of the disc.

2, flanged butterfly valve

Flanged butterfly valve is a vertical plate structure, and the valve stem is the sealing ring of the integral metal hard seal valve

The composite structure of flexible graphite plate and stainless steel plate is installed on the valve body, and the sealing surface of the butterfly plate is welded with stainless steel. The sealing ring of the soft seal valve is made of nitrile rubber and is mounted on the butterfly plate.

3, lug type butterfly valve

4. Welded butterfly valve

Welding butterfly valve is a kind of non-closed butterfly valve, widely used in building materials, metallurgy, mining, electric power and other production process medium temperature ≤300℃ nominal pressure of 0.1Mpa on the pipeline, used to connect, open and close or adjust the medium quality.

The electrically regulated butterfly valve belongs to a variety of electric valves and electric regulating valves. The main connection methods are: flange type and sandwich type, which is an important execution unit in the field of industrial automation control. Electric adjustment butterfly valve installation points two analysis: installation position, height, import and export direction must meet the design requirements, pay attention to the direction of the medium flow should be consistent with the direction of the arrow marked on the valve body, the connection should be firm and tight. Electric adjustment butterfly valve must be inspected before installation, valve nameplate should comply with the current national standard "General valve mark" GB12220 provisions. For valves whose working pressure is greater than 1.0MPa and which play a cutting role on the main pipe, strength and tight performance tests should be carried out before installation. Only qualified can be used. During the strength test, the test pressure is 1.5 times the nominal pressure, the duration is not less than 5min, and the valve shell and packing should be qualified without leakage. The electric butterfly valve can be divided into offset plate, vertical plate, inclined plate and lever type according to the structure; According to the seal form can be divided into soft seal type and hard seal type two; The soft seal type is generally sealed by rubber ring, and the hard seal type is usually sealed by metal ring.

Functional use

The butterfly valve is usually less than 90°, the butterfly valve and the butterfly rod itself have no self-locking ability, in order to position the butterfly plate, the worm gear reducer should be installed on the valve stem. The use of worm gear reducer can not only make the butterfly plate self-locking ability, so that the butterfly plate stops in any position, but also improve the operating performance of the valve. The characteristics of industrial special butterfly valve: high temperature resistance, the applicable pressure range is also high, the nominal diameter of the valve is large, the valve body is made of carbon steel, and the sealing ring of the valve plate is made of metal ring instead of rubber ring. Large high temperature butterfly valve is made of steel plate welding, mainly used in high temperature medium smoke duct and gas pipeline.

Select and use

The butterfly plate of the butterfly valve is installed in the diameter direction of the pipe. Butterfly valve has simple structure, small size, light weight, only a few parts, and only need to rotate 90 degrees to quickly open and close, simple operation, and 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 resistance of the medium flowing through the valve body, so the pressure drop generated by the valve is small, so it has better flow control characteristics.

If the butterfly valve is required to be used as a flow control, the main thing is to correctly select the size and type of valve. The structure principle of butterfly valve is especially suitable for the production of large diameter valves. Commonly used butterfly valves are clamping butterfly valves and flanged butterfly valves. Clamping butterfly valve is used to connect the valve between the two pipe flanges with double-headed bolts, flanged butterfly valve is a valve with a flange, and the two ends of the valve are connected to the pipe flange with bolts.

As a component used to realize the on-off and flow control of pipeline system, butterfly valve has been widely used in many fields such as petroleum, chemical industry, metallurgy, hydropower and so on. In the well-known butterfly valve technology, the sealing form is mostly sealed structure, and the sealing material is rubber, polytetrafluoroethylene and so on. Due to the limitations of structural characteristics, it is not suitable for high temperature, high pressure, corrosion resistance, wear resistance and other industries.

A relatively advanced butterfly valve is a three-eccentric metal hard seal butterfly valve, the valve body and the valve seat are connected components, and the valve seat sealing surface layer is surfacing welded with temperature resistant and corrosion resistant alloy materials. The multi-layer soft stacked sealing 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, friction-free opening and closing. When closing, it compensates for the sealing with the increase of the torque of the transmission mechanism, which improves the sealing performance of the butterfly valve and prolonging the service life.

However, the following problems still exist in the use of this butterfly valve:

First, because the multi-layer soft and hard stacked sealing ring is fixed on the valve plate, when the valve plate is normally open, the medium forms a positive scouring on the sealing surface, and the soft sealing belt in the metal sandwich is washed, which directly affects the sealing performance.

Second, limited by the structural conditions, the structure is not suitable for valves below the diameter DN200, because the overall structure of the valve plate is too thick and the flow resistance is large.

Third, because of the principle of the three-eccentric structure, the sealing between the sealing surface of the valve plate and the seat is by the torque of the transmission device to press the valve plate to the seat. In the positive flow state, the higher the medium pressure, the tighter the seal extrusion. When the flow channel medium countercurrent with the increase of medium pressure, the unit positive pressure between the valve plate and the seat is less than the medium pressure, the seal begins to leak.

The high-performance three-eccentric bidirectional hard seal 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 inclined conical structure, and the temperature and corrosion resistant alloy material is surfacing on the inclined conical surface of valve plate. The structure of the spring fixed between the adjusting ring platen and the adjusting bolt on the platen.

This structure effectively compensates the tolerance zone between the 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 interchangeable medium transportation. The sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shape, which has the dual advantages of metal hard seal and soft seal, and has zero leakage sealing performance under both low and high temperature conditions.

The test proves that the pressure of the sealing surface is caused by the torque of the transmission device and the effect of the medium pressure on the valve plate when the flow direction of the medium is the same as the rotation direction of the butterfly plate. When the positive medium pressure increases, the more tightly the inclined cone surface of the valve plate and the sealing surface of the seat are squeezed, the better the sealing effect is. When countercurrent, the seal between the valve plate and the seat depends on the torque of the driving device to press the valve plate against the seat. With the increase of the reverse medium pressure, when the unit positive pressure between the valve plate and the seat is less than the medium pressure, the deformation energy stored by the spring of the adjustment ring compensates the tight pressure of the valve plate and the seat sealing surface automatically. Therefore, the utility model does not install a soft and hard multi-layer sealing ring on the valve plate as the prior technology, but is directly installed on the valve body, and an adjustment ring is added in the middle of the pressure plate and the seat, which is a very ideal bidirectional hard sealing method. It will replace gate valves, globe valves and ball valves.

Applicable occasion

Butterfly valves are suitable for flow regulation. Because the pressure loss of the butterfly valve in the pipeline is relatively large, the robustness of the butterfly plate under the pressure of the pipeline medium should also be considered when it is closed. In addition, the operating temperature limitations of the elastic seat material at high temperatures must be considered. The structure length and overall height of the butterfly valve are small, the opening and closing speed is fast, and the butterfly valve has good fluid control characteristics, and the structure principle of the butterfly valve is most suitable for the production of large diameter valves. When the butterfly valve is required to be used for flow control, the most important thing is to correctly select the size and type of the butterfly valve so that it can work properly and effectively.

Generally, in throttling, regulating control and mud media, short structural length and fast opening and closing speed (1/4 RPM) are required. Low pressure cut-off (small pressure difference), butterfly valve is recommended.

The butterfly valve can be used when the two-position adjustment, the shrinking ground channel, the low noise, the cavitation and gasification phenomenon, the small leakage to the atmosphere, and the abrasive medium.

When the butterfly valve is used under special working conditions for throttling adjustment, or when the seal is strictly required, or when the butterfly valve is used under working conditions such as severe wear and low temperature (cryothermia), it is necessary to use a specially designed three-eccentric or double-eccentric butterfly valve with a specially designed metal seal and adjustment device.

The butterfly valve is suitable for fresh water, sewage, sea water, salt water, steam, natural gas, food, medicine, oil and various acid and alkali and other pipelines that require complete sealing, zero gas test leakage, high life requirements, and working temperatures of -10 degrees to 150 degrees.

The soft-sealed eccentric butterfly valve is suitable for bidirectional opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in metallurgy, light industry, electric power, petrochemical system gas pipelines and waterways.

Metal to metal wire sealed double eccentric butterfly valve is suitable for city heating, gas supply, water supply and other gas, oil, acid and alkali pipelines, as a regulating and throttling device.

In addition to being used as the program control valve of large pressure swing adsorption (PSA) gas separation device, the metal to metal surface sealed three eccentric butterfly valve can also be widely used in petroleum, petrochemical, chemical, metallurgy, electric power and other fields, and is a good alternative to gate valve and globe valve

Common fault

The rubber elastomer in the butterfly valve will tear, wear, aging, perforation and even fall off during continuous use. The traditional hot vulcanization process is difficult to adapt to the needs of on-site repair, repair to use special equipment, consume a lot of heat and electric energy, time-consuming and laborious. Nowadays, polymer composite materials are gradually used to replace the traditional methods, among which the most widely used is the Fushi Blue technology system. The superior adhesion and excellent wear and tear resistance of its products ensure that the repair reaches or even exceeds the service life of the new parts, greatly reducing the downtime.

Installation and maintenance

1. During installation, the valve disc should be stopped in the closed position.

2, the opening position should be determined according to the rotation Angle of the butterfly plate.

3. The butterfly valve with a bypass valve should be opened before opening.

4, should be installed according to the manufacturer's installation instructions, large weight butterfly valve, should be set a solid foundation.

Construction and installation points

1, the installation position, height, import and export direction must meet the design requirements, the connection should be firm and tight. 2), all kinds of manual valves installed on the insulation pipeline, the handle shall not be downward.

2, the valve must be inspected before installation, the valve nameplate should comply with the current national standard "General valve mark" GB 12220 provisions. For valves with working pressure greater than 1.0MPa and that play a cutting role on the main pipe, strength and tight performance tests should be carried out before installation, and qualified before use. During the strength test, the test pressure is 1.5 times the nominal pressure, the duration is not less than 5min, and the valve shell and packing should be qualified without leakage. During the tightness test, the test pressure is 1.1 times of the nominal pressure; The test pressure should meet the requirements of GB 50243 standard for the duration of the test, and the valve disc sealing surface should be qualified without leakage.

Key points of product selection

1. The main control parameters of butterfly valve are specifications and sizes.

2, butterfly valve is a single plate air valve, its structure is simple, easy to process, low cost, easy to operate, but the adjustment accuracy is poor, only suitable for ventilation and air conditioning system as a switch or rough adjustment occasions.

3, manual, electric or zipper operation, can be fixed at any Angle within 90° range.

4, due to the single shaft single valve plate, the bearing capacity is limited, and the service life of the valve is short under the conditions of large pressure difference and large flow rate. The valve is divided into closed type and ordinary type, heat preservation and non-heat preservation.

5, the electric butterfly valve is only two-position control, the electric actuator is the same as the multi-leaf valve.

Installation matters

Butterfly valve simple structure, small size, light weight, its components are relatively few, the key components can form a butterfly valve, open the time is also very convenient, only need to choose the switch to 90 degrees can be, butterfly valve fluid control is very good, can increase the flow or reduce the flow at any time, valve in the transport of any fluid when there is a certain resistance, The resistance of the butterfly valve mainly comes from itself, such as the thickness of the butterfly valve body, if you want to reduce the resistance to the fluid, you only need to reduce its thickness.

Elastic seals have temperature-limited defects.

The application range of butterfly valve is also relatively wide, if it is used to control the flow rate, it is necessary to choose a different type and the size of the valve body, because the butterfly valve itself is more suitable for some valves with relatively large caliber when it is designed. Butterfly valve is not only widely used in petroleum, gas, chemical industry, water treatment and other general industry, but also used in the cooling water system of thermal power station.