[Science stickers] The role and classification of valves

Valves are generally divided into automatic valves and actuated valves. Automatic valves (such as safety valves, pressure reducing valves, steam traps and check valves) rely on changes in the medium pressure of the equipment or pipeline to achieve the purpose of opening and closing. Drive the valve (gate valve, globe valve, ball valve, butterfly valve, etc.) through the driving device (manual, electric, hydraulic, pneumatic, etc.) to adjust the pressure, flow and direction of the medium in the pipeline. Because the pressure, temperature, flow rate and physical and chemical properties of the medium are different, the control requirements and use requirements of the equipment and piping systems are also different, so the role of the valve is also different.

Classified by valve function:

Stop valve: The stop valve is also called a closed-circuit valve, and its function is to connect or cut off the medium in the pipeline. Globe valves include gate valves, globe valves, plug valves, ball valves, butterfly valves and diaphragm valves.
Regulating valve: Regulating valve includes regulating valve, throttle valve and pressure reducing valve. Its function is to adjust the pressure, flow and other parameters of the medium.
Check valve: Check valve is also called check valve or check valve, its function is to prevent pipeline media from backflow. The bottom valve of the pump is also a check valve.
Safety valve: The function of the safety valve is to prevent the pressure of the medium in the pipeline or equipment from exceeding the specified value, so as to achieve the purpose of safety protection.
Diversion valve: Diversion valves include various distribution valves, traps, etc. The function of the diverter valve is to distribute, separate or mix the medium in the pipeline.
Exhaust valve: The exhaust valve is an indispensable auxiliary component in the piping system. It is usually installed at altitude or elbows to eliminate excess gas in the pipeline, improve road efficiency and reduce energy consumption.

The role of the valve

1. Cut-off effect
The important role of the valve is the cut-off effect. It is to close (close) the fluid in the pipeline without causing it to flow. Under normal circumstances, the valves of various pipelines mainly play a cut-off role.
 
2. Adjustment function
Another important function of the valve is to adjust the flow rate. According to the working conditions or requirements, adjust the medium flow rate, temperature, pressure, liquid level and other parameters. The flow control depends on the adjustment of the valve opening. [Electric regulating ball valve Electric regulating butterfly valve Pneumatic regulating ball valve Pneumatic regulating butterfly valve]
 
3. Non-
reverse function Some pipelines require medium flow to flow in one direction, and no reverse flow or rewinding is allowed. This requires the use of check valves (or check valves). It refers to a valve that automatically opens and closes the disc to prevent the backflow of the medium. Belongs to an automatic valve. Its main function is to prevent the reverse flow of the medium, prevent the reverse rotation of the pump and the drive motor, and the discharge of the container medium.
 
4. Safety function 
When the fluid pressure is too high, in order to prevent the pressure in the high-pressure container from exceeding the pressure limit of the container, an explosion may occur. Therefore, a valve that can automatically release pressure under a certain pressure is installed on the container, usually called a safety valve. For example, safety valves are installed on boilers, compressed air tanks and some high-pressure reactors. The valve plays a role in ensuring safety.
 
5. Other functions
In addition to the above four functions, the valve also has some functions, such as stabilizing the system pressure; decompressing the high pressure before the valve to decompression, decompressing the exhaust gas, and discharging pollutants from the discharge function. Sampling for analysis and observation; and a part of the fluid is returned to the previous recirculation process for recirculation. There are also steering valves (three-way valve, four-way valve, etc.) to transfer fluid to another line.

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