Click on the alphabetic index to display terms beginning with the corresponding letter or search for a term below.

Penstock valve

A type of simple gate valve, used to contain fluids in open channels. Often found in waste water treatment plants.

Pilot valve

Small valve requiring little power which is used to operate a larger valve. See also solenoid valves.

Pinch valve

A valve in which a flexible hose is pinched between one or two moving external elements to stop the flow. This valve is often used in slurry and mining applications, as its operation is not affected by solid matter in the medium. It is also used with certain gases, as the absence of possible leak paths to the atmosphere ensures good emission control.

Plug valve

This multi-turn valve derives its name from the rotating plug which forms the closing element. The plug may be cylindrical or truncated. In the open position, the fluid flows through a hole in the plug. Lubricated plug valves rely on a sealing compound injected between the plug and the valve body, whilst sleeved plug valves are fitted with a ‘soft’ insert between the plug and the body.

Pneumatic actuator

A device fitted to the valve stem than uses pneumatic energy to open/close or regulate the valve. Depending on the configuration, the compressed air may both open and close the valve, or just open the valve. In that latter case, a spring will typically be fitted inside the actuator to return the valve to the closed position.


Device that ensures the closing or throttling element of a valve moves to or maintains the correct position.

Pressure reducing valve

A self-operating valve used to reduce any excess pressure in a system, eg steam. Also known as a PRV. The valve opens if the internal pressure exceeds that holding the closing element onto the seat.

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