1. Gate Valves:
Gate valve refers to a valve in which the closing member (gate plate) moves in the vertical direction of the axis of the channel. It is mainly used as cutting off medium in the pipeline, that is, fully open or fully closed. Generally, gate valves cannot be used as flow regulators. It can be used for low temperature and low pressure as well as high temperature and high pressure. However, the gate valve is generally not used in pipelines that transport mud and other media.
Advantages：
- Low fluid resistance
- Small torque required for opening and closing
- It can be used in the ring network pipeline where the medium flows in both directions, which means that the flow direction of the medium is not restricted
- When it’s fully open, the sealing surface is less eroded by the working medium than the globe valve
- It’s structure is simple, and the manufacturing technology is good
- Shorter structure length
Disadvantages：
- Large dimensions and opening heights require larger installation space
- In the process of opening and closing, the sealing surface is relatively frictional, and the abrasion is large, and it is easy to cause sealing surface abrasion even at high temperature
- Generally, the gate valve has two sealing surfaces, which adds some difficulties for processing, grinding and maintenance
- Long opening and closing time
2. Butterfly valve
The butterfly valve is a valve to open, close and regulate the flow channel with a disc-shaped opening and closing part reciprocating about 90°.
Advantages：
- Simple structure, small size, light weight and low consumables
- Quick opening and closing, small flow resistance
- It can be used for medium with suspended solid particles, and it can also be used for powder and granular media depending on the strength of the sealing surface
Disadvantages：
- The flow adjustment range is not large. When it open up to 30%, the flow will be over 95%
- Due to the structure of the butterfly valve and the limitation of the sealing material, it is not suitable for high temperature and high pressure piping systems. Normal working temperature is below 300 ℃, and pressure below PN40
- Compared with ball valves and globe valves, the sealing performance is relatively poor, so it is used in places where sealing requirements are not very high
3. Ball valve
It is evolved from the plug valve. Its opening and closing part is a sphere. The sphere is rotated 90 ° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the medium flow direction of the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function.
Advantages：
- The lowest flow resistance (actually 0).
- Because it does not get stuck during work (without lubricant), it can be reliably used in corrosive media and low boiling liquids.
- Fully sealed can be achieved over a wide range of pressures and temperatures.
- It can achieve fast opening and closing, the opening and closing time of some structures is only 0.05 ~ 0.1s to ensure that it can be used in the automated system of the test bench. Shock-free operation when opening and closing the valve quickly.
- Spherical closure can be positioned automatically at the boundary position.
- Reliable sealing of working medium on both sides.
- When fully open and fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface.
- Compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic medium systems.
- The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline.
- The shut-off parts can withstand the high pressure difference when closing.
- The fully welded ball valve can be directly buried into the ground, so that the internal parts of the valve are not eroded, and the maximum service life is 30 years, it is the best ideal valve for oil&gas pipelines.
Disadvantages：
- The main valve seat sealing material of the ball valve is PTFE, it is inert to almost all chemicals, and it has comprehensive characteristics such as small coefficient of friction, stable performance, not easy to age, wide temperature range and excellent sealing performance. However, the physical characteristics of PTFE, including higher expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of the valve seat seal must be based on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is damaged. Moreover, PTFE has a low temperature resistance grade and can only be used at temperatures below 180 ° C. Beyond this temperature, the sealing material will age. In the case of long-term use, it is generally used at or below 120 ° C.
- Its regulating performance is worse than that of globe valves, especially pneumatic valves (or electric valves).
4. Globe valve：
It is refers to a valve in which the closure (valve clack) moves along the center-line of the seat. According to this type of movement of the valve clack, the change of the valve seat port is proportional to the valve clack stroke. Because this type of valve has a relatively short opening and closing stroke, and has a very reliable shut-off function, and also because the change in the valve seat port is proportional to the stroke of the valve clack, it is very suitable for regulating flow. Therefore, this type of valve is very suitable for shut-off or regulation and throttling.
Advantages：
- During the process of opening and closing, the friction between the valve clack and the sealing surface of the valve body is smaller than that of the gate valve, so it is more wear-resistant.
- The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than the gate valve.
- Generally, there is only one sealing face on the body and valve clack, so it has better manufacture technology and easier to maintain.
- Because the packing is generally a mixture of asbestos and graphite, the temperature resistance grade is higher. Generally steam valves are globe valves.
Disadvantages：
- Because the flow direction of the medium through the valve changes, the minimum flow resistance of the globe valve is also higher than most other types of valves.
- Slower opening speed than ball valves due to longer stroke.
5. Plug valve
It is a rotary valve with a plunger-shaped closing part, through 90 ° rotation, the channel port on the valve plug is connected with or separated from the channel port on the valve body to realize open or close. Plug shape can be cylindrical or conical. Its principle is basically similar to the ball valve. The ball valve was developed on the basis of the plug valve. It is mainly used in oilfield extraction and also be used in petrochemical industry.
6. Safety valve
The safety valve is used as an over-pressure protection device on a pressure vessel, equipment or pipeline. When the pressure in the equipment, container or pipeline rises above the allowable value, the valve automatically opens, and then the entire volume is discharged to prevent the pressure in the equipment, container or pipeline continuing to rise; when the pressure drops to the specified value, the valve should close in time to ensure the equipment, containers or pipelines can be operated safely.
7. Steam hydrophobic valve
During the transportation of steam, compressed air and other media, some condensation water will be formed. In order to ensure the efficiency and safe operation of the device, these useless and harmful media should be discharged in time to ensure the consumption and use of the device.
It has the following functions:
- quickly remove the condensate water ;
- prevent steam leakage;
- exclude air and other non-condensable gases.
8. Pressure reducing valve
It is a valve that adjusts the inlet pressure to a required outlet pressure and relies on the energy of the medium to keep the outlet pressure automatically stable.
9. Check valve
It is also known as reverse flow valve, non-return valve, back pressure valve and one way valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, which belongs to an automatic valve.
Check valve is used in piping system. Its main function is to prevent the medium from flowing backwards, to prevent the pump and the drive motor from reversing, and to release the medium from the container. The check valve can also be used to supply pipelines whose auxiliary pressure may rise above the system pressure. It can be divided into swing-type (rotation according to the center of gravity) and lift-type (moving along the axis).