While understanding and mastering the steps of valve selection, we should also further understand the basis of valve selection.
(1) The use, working conditions and control mode of the selected valve.
(2) the nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether it is toxic, whether it is flammable and explosive, and the viscosity of the medium.
(3) Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
(4) Installation size and total size requirements: nominal diameter, connection mode and size with pipe, total size or weight limit, etc.
(5) Additional requirements for reliability, service life and explosion-proof performance of electric devices of valve products.
When selecting parameters, note the following:
If the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, normal flow pressure drop, pressure drop when closed, and maximum and minimum inlet pressure of the valve.
According to the above selection of valve basis and steps, in a reasonable and correct selection of valves, must be a detailed understanding of the internal structure of various types of valves, so as to make the right choice on the preferred valve.
The ultimate control of the pipe is the valve. The opening and closing part of the valve controls the flow pattern of the intermediate pipe. The shape of the valve channel makes the valve have certain flow characteristics. This must be taken into account when selecting the valves most suitable for installation in piping systems.
Valve selection should follow the principles:
1. Valves for cutting off and opening media
Flow path for through valve, flow resistance is small, usually used as the valve to cut off and open the medium of the valve. Downward closed valve (
Globe Valve, plunger valve) because of its tortuous flow path, flow resistance is larger than other valves, so less choice. Closed valves can be used if flow resistance is allowed to be large.
2. Flow control valve
Generally choose easy to adjust the flow of the valve as the control flow. Downward shutoff valves, such as globe valves, are suitable for this purpose because their seat size is proportional to the stroke of the closing section. Rotary valves (plug, butterfly, ball valves) and flexible body valves (pinch, diaphragm) can also be used for throttling control, but usually only in a limited valve diameter range. The
Gate Valve uses a disc gate for lateral motion to the circular seat. It only controls flow well when near the off position, so it is not usually used for flow control.
3. Reversing and steering valves
The valve can be provided with three or more channels according to the need of reversing and diverting. Plug and ball valves are more suitable for this purpose. Therefore, most valves used for reversing and steering are selected from these valves. However, in some cases, other types of valves may be used for reversing and diverting as long as two or more valves are properly connected to each other.
4. Valves for suspended particle medium
When there are suspended particles in the medium, when its closed part slides along the sealing surface, it is best to use a valve with a wiping function. If the closing section is perpendicular to the back and forth motion of the seat, the particle may be caught. Therefore, this valve is only suitable for basically clean media, unless the sealing material can allow particles to embed. Ball valves and plug valves can wipe the sealing surface during opening and closing, so they are suitable for media with suspended particles.
WUXI KVC-VALVE