In the face of so many valve classification and so complex conditions, to choose the most suitable valve for pipeline system installation, we should first understand the characteristics of the valve; Secondly, we should master the steps and basis of valve selection; Furthermore, we should follow the principle of selecting valves for petroleum and chemical industry.
The principle of selecting valves in petroleum and chemical industry: the flow passage is straight through valve, which has small flow resistance, and usually is used as cut-off and open medium valve; The valve which is easy to adjust the flow is used to control the flow; Plug valve and ball valve are suitable for reversing and diverting; The valve with wiping function is suitable for medium with suspended particles.
01. Valves for closing and opening media
The flow channel is straight through valve, and its flow resistance is small. It is usually selected as the valve for cut-off and open medium. Downward closing valve (stop valve, plunger valve) is less used because of its tortuous flow channel and higher flow resistance than other valves. Closed type valve can be selected when higher flow resistance is allowed.
02. Valve for flow control
Usually choose easy to adjust the flow of the valve as control flow. A downward closing valve, such as a globe valve, is suitable for this purpose because its seat size is proportional to the stroke of the closing element. Rotary valve (plug valve, butterfly valve, ball valve) and flex body valve (clamp valve, diaphragm valve) can also be used for throttling control, but usually only in a limited range of valve diameter. Gate valve is a disc-shaped gate to cross cut the round valve seat. It can control the flow only when it is close to the closed position, so it is not usually used for flow control.
03. Valve for reversing and diverting
The valve can have three or more channels according to the need of directional diversion. Plug valve and ball valve are more suitable for this purpose, therefore, most of the valves used for directional diversion are selected as one of the plug valve and ball valve. But in some cases, other types of valves, as long as two or more valves are properly connected with each other, can also be used for diversion.
04. Valve for medium with suspended particles
When there are suspended particles in the medium, it is most suitable for the valve with the function of wiping by sliding the closing part along the sealing surface. If the back and forth movement of the closing part to the seat is vertical, particles may be trapped. Therefore, this kind of valve is only suitable for basically clean medium unless the sealing surface material can allow particles to be embedded. Ball valve, plug valve and butterfly valve can wipe the sealing surface in the process of opening and closing, so they are suitable for medium with suspended particles.