1. Cutting and releasing the medium
This is the most basic function of the valve. Usually, the valve with a straight-through flow channel is selected, and its flow resistance is small.
Downward closed valves (stop valve, plunger valve) are less used because of their tortuous flow paths and higher flow resistance than other valves. Where higher flow resistance is allowed, a closed valve can be selected.
2. Control the flow
Usually, the valve that is easy to adjust the flow is selected as the control flow. Downward closing valves (such as globe valves) are suitable for this purpose because of the proportional relationship between the size of the seat and the travel of the closing member.
Rotary valves (plug valves, butterfly valves, ball valves) and flexible body valves (pinch valves, diaphragm valves) can also be used for throttling control, but usually only within a limited range of valve sizes.
The gate valve uses a disc-shaped gate to make a transverse movement to the circular valve seat mouth. It can control the flow well only when it is close to the closed position, so it is usually not used for flow control.
Three, commutation shunt
This valve can have three or more passages depending on the need for reversing and diverting. Plug valves and ball valves are more suitable for this purpose, so most of the valves used for reversing and diverting are selected from one of these types of valves.
In some cases, however, other types of valves can also be used for reversing and diverting, as long as two or more valves are properly connected to each other.
4. Media with suspended particles
When there are suspended particles in the medium, it is more suitable to use a valve whose closing member slides along the sealing surface with a wiping effect.
If the back and forth movement of the closure member to the valve seat is vertical, particles may be trapped, so this valve is only suitable for basically clean media unless the sealing surface material can allow particles to be embedded. The ball valve and the plug valve have a wiping effect on the sealing surface during the opening and closing process, so they are suitable for use in the medium with suspended particles.