(1) Valves for closing and opening media
The flow path is a straight-through valve with a small flow resistance and is usually selected as a valve for cut-off and open media. Down-closed valves (shut-off valves, plunger valves) are less preferred because of their tortuous path and higher flow resistance than other valves. Where a higher flow resistance is allowed, a closed valve can be used.
(2) Valves for controlling flow
A valve that is easy to adjust the flow rate is usually selected as the control flow. A down-closed valve (such as a shut-off valve) is suitable for this purpose because its seat size is proportional to the stroke of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexing valve body valves (clamping valves, diaphragm valves) can also be used for throttling control, but are usually only available in a limited range of valve sizes. The gate valve is a cross-cut movement of the circular valve seat with a disc-shaped shutter. It can control the flow better only when it is close to the closed position, so it is usually not used for flow control.
(3) Valves for commutating split
This valve can have three or more passages depending on the need for a commutation split. Plug valves and ball valves are more suitable for this purpose, so most of the valves used for commutating splits select one of these types of valves. However, in some cases, other types of valves may be used for commutation splitting by simply interconnecting two or more valves.
(4) Valves for media with suspended particles
When the medium has suspended particles, it is most suitable to use a valve with a wiping action of the sliding member along the sealing surface. If the closing movement of the closure to the valve seat is vertical, it is possible to hold the particles, so that the valve is only suitable for substantially clean media unless the sealing surface material allows for the incorporation of particles. The ball valve and the plug valve have a wiping action on the sealing surface during the opening and closing process, so it is suitable for use in a medium with suspended particles.
At present, in the petroleum, chemical, and other industries, the valve application, operating frequency and service are ever-changing. To control or eliminate even the slightest leakage, the most important and critical equipment is the valve.