2.5 Plug valve

Plug valve is a valve that uses a plug body with a through hole as the opening and closing part, and the plug body rotates with the valve stem to achieve opening and closing. The plug valve has a simple structure, quick opening and closing, easy operation, small fluid resistance, few parts and light weight. Plug valves are available in straight-through, three-way and four-way types. The straight-through plug valve is used to cut off the medium, and the three-way and four-way plug valves are used to change the direction of the medium or divert the medium.

2.6 Butterfly valve

Butterfly valve is a butterfly plate that rotates 90° around a fixed axis in the valve body to complete the opening and closing function. Butterfly valves are small in size, light in weight and simple in structure, consisting of only a few parts.

And it can be opened and closed quickly by just rotating 90°, which is easy to operate. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body. Therefore, the pressure drop generated by the valve is very small, so it has good flow control characteristics. Butterfly valves are divided into two sealing types: elastic soft seal and metal hard seal. Elastic sealing valve, the sealing ring can be embedded in the valve body or attached to the periphery of the butterfly plate. It has good sealing performance and can be used for throttling, medium vacuum pipelines and corrosive media. Valves with metal seals generally have a longer service life than valves with elastic seals, but it is difficult to achieve complete sealing. They are usually used in situations where flow and pressure drop changes greatly and good throttling performance is required. Metal seals can adapt to higher operating temperatures, while elastic seals have the disadvantage of being limited by temperature.

2.7 Check valve

The check valve is a valve that can automatically prevent the reverse flow of fluid. The disc of the check valve opens under the action of fluid pressure, and the fluid flows from the inlet side to the outlet side. When the pressure on the inlet side is lower than the outlet side, the valve disc automatically closes under the action of fluid pressure difference, its own gravity and other factors to prevent fluid from flowing back. According to the structural form, it can be divided into lift check valve and swing check valve. The lifting type has better sealing and greater fluid resistance than the swing type. For the suction inlet of the pump suction pipe, a bottom valve should be used. Its function is to fill the pump inlet pipe with water before starting the pump; after stopping the pump, keep the inlet pipe and pump body filled with water in preparation for starting again. The bottom valve is generally only installed on the vertical pipe at the pump inlet, and the medium flows from bottom to top.

2.8 Diaphragm valve

The opening and closing part of the diaphragm valve is a rubber diaphragm, which is sandwiched between the valve body and the valve cover.

The middle protruding part of the diaphragm is fixed on the valve stem, and the valve body is lined with rubber. Since the medium does not enter the inner cavity of the valve cover, the valve stem does not require a stuffing box. The diaphragm valve has a simple structure, good sealing performance, easy maintenance, and low fluid resistance. Diaphragm valves are divided into weir type, straight-through type, right-angle type and direct-flow type.

3. Commonly used valve selection instructions

3.1 Gate valve selection instructions

Under normal circumstances, gate valves should be preferred. In addition to being suitable for steam, oil and other media, gate valves are also suitable for media containing granular solids and high viscosity, and are suitable for valves in venting and low vacuum systems. For media containing solid particles, the gate valve body should be equipped with one or two purge holes. For low-temperature media, low-temperature special gate valves should be selected.

3.2 Instructions for selection of stop valves

The stop valve is suitable for pipelines with lax requirements on fluid resistance, that is, pressure loss is not considered much, and pipelines or devices with high temperature and high pressure media. It is suitable for steam and other medium pipelines with DN <200mm; small valves can use cut-off valves. Valves, such as needle valves, instrument valves, sampling valves, pressure gauge valves, etc.; stop valves have flow adjustment or pressure adjustment, but the adjustment accuracy is not required, and the pipeline diameter is relatively small, so a stop valve or throttling valve should be used Valve; For highly toxic media, a bellows-sealed stop valve should be used; however, the stop valve should not be used for media with high viscosity and media containing particles that are prone to sedimentation, nor should it be used as a vent valve and a valve in a low vacuum system.

3.3 Ball valve selection instructions

Ball valves are suitable for low-temperature, high-pressure, and high-viscosity media. Most ball valves can be used in media with suspended solid particles, and can also be used in powdery and granular media according to the sealing material requirements; full-channel ball valves are not suitable for flow regulation, but are suitable for occasions requiring rapid opening and closing, which is easy to implement. Emergency cut-off in accidents; usually recommended in pipelines with strict sealing performance, wear, shrinkage channels, rapid opening and closing movements, high-pressure cutoff (large pressure difference), low noise, gasification phenomenon, small operating torque, and small fluid resistance. Use ball valves; ball valves are suitable for light structures, low-pressure cut-offs, and corrosive media; ball valves are also the most ideal valves for low-temperature and cryogenic media. For piping systems and devices with low-temperature media, low-temperature ball valves with valve covers should be used; choose When using a floating ball valve, its seat material should bear the load of the ball and the working medium. Large-diameter ball valves require greater force during operation. Ball valves with DN ≥ 200mm should use worm gear transmission; fixed ball valves are suitable for larger diameters and High-pressure situations; in addition, ball valves used in process pipelines for highly toxic materials and flammable media should have fire-proof and anti-static structures.

3.4 Throttle valve selection instructions

The throttle valve is suitable for occasions where the medium temperature is low and the pressure is high. It is suitable for parts that need to adjust the flow rate and pressure. It is not suitable for media with high viscosity and solid particles, and is not suitable for use as a isolation valve.

3.5 Plug valve selection instructions

Plug valve is suitable for occasions requiring rapid opening and closing. It is generally not suitable for steam and medium with higher temperature. It is used for medium with lower temperature and high viscosity, and is also suitable for medium with suspended particles.

3.6 Butterfly valve selection instructions

Butterfly valves are suitable for situations with large diameters (such as DN﹥600mm) and short structural lengths, as well as situations where flow adjustment and fast opening and closing are required. They are generally used for water, oil and compression products with temperatures ≤80°C and pressures ≤1.0MPa. Air and other media; because the pressure loss of butterfly valves is relatively large compared to gate valves and ball valves, butterfly valves are suitable for pipeline systems with loose pressure loss requirements.

3.7 Check valve selection instructions

Check valves are generally suitable for clean media and are not suitable for media containing solid particles and high viscosity. When DN ≤ 40mm, a lift check valve should be used (only allowed to be installed on horizontal pipes); when DN = 50 ~ 400mm, a swing lift check valve should be used (can be installed on both horizontal and vertical pipes, If installed on a vertical pipeline, the medium flow direction should be from bottom to top); when DN ≥ 450mm, a buffer check valve should be used; when DN = 100 ~ 400mm, a wafer check valve can also be used; a swing check valve The return valve can be made to have a very high working pressure, PN can reach 42MPa, and it can be applied to any working medium and any working temperature range depending on the materials of the shell and seals. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196~800℃.

3.8 Diaphragm valve selection instructions

The diaphragm valve is suitable for oil, water, acidic media and media containing suspended solids with an operating temperature of less than 200°C and a pressure of less than 1.0MPa. It is not suitable for organic solvents and strong oxidant media. Weir type diaphragm valves should be selected for abrasive granular media. When selecting a weir type diaphragm valve, refer to its flow characteristics table; viscous fluids, cement slurries and precipitating media should use straight-through diaphragm valves; except for specific requirements, diaphragm valves should not be used in vacuum pipelines and vacuum equipment.