Water hammer: Occurs in a piping system due to rapid fluctuations in pressure. Usually caused by change in pump conditions, or the opening or closing of a valve too rapidly.
Water horse power (WHP): The horse power equivalent of the pump calculated by using the following formula = head x gpm / 3960.
Water NPSHR: The net positive suction head (NPSHR) required. This is the suction required by a pump when it is pumping water. It is used as baseline value for estimating its NPSHR when pumping other types of liquid.
Watt: A measure of work. The rate at which work is done when an object’s velocity is held constant against an opposing force of one Newton. (Units are Newton meters/second).
Wave spring: A special washer that is used in mechanical seals when axial space is at a premium.
Wear ring: Restricts leakage from the discharge to the inlet on closed impeller pumps and should be replaced when the recommended clearance is doubled.
Welded metal bellows: A mechanical seal design that uses metal instead of elastomer. Excellent for cryogenic and hot applications.
Wet critical speed: API 610 d The critical speed of a rotor that includes the considerations of the pumped fluid. Compare to dry critical speed.
Wet end: The components of the pump that get wet from pumping the fluid. Stuffing box, impeller, volute, etc.
Wetted surface: Any of the internal surfaces of a pump that comes into contact with the process fluid.
Wobble plate: A plate that attaches to a rotating component to reduce vibration at high speeds by correcting the balance.