Water hammer

Water hammer is a pressure surge caused by a rapid change in water velocity inside a pipe. The resulting pressure wave can produce noise, vibration, and damaging loads.

Joukowsky equation: An equation relating a sudden fluid-velocity change to the resulting pressure change in a pipe. It estimates the surge from the velocity change and wave speed.
Surge tank: A chamber connected to a pipeline that absorbs or supplies liquid during transient flow changes. It buffers flow changes and limits pressure excursions in long pipelines.
Valve closure: The stopping of flow by moving a valve toward its closed position. Rapid closure is a common trigger for water hammer in plumbing and pipelines.
Steady-state flow: Fluid flow whose properties at each location do not change with time. Water hammer is a transient event, unlike flow conditions that remain constant.
Pressure wave: A traveling disturbance in pressure that propagates through a medium. Water hammer propagates as a pressure wave through the pipe and its contents.
Water hammer arrestor: A device that cushions pressure surges, usually with a compressible gas chamber or spring-loaded piston. It absorbs abrupt flow stoppages near fixtures and appliances.
Pump trip: The sudden loss of a pump's drive or power, interrupting its contribution to system flow. A pump trip can create a pressure drop and subsequent surge as flow reverses or changes.
Water hammer in steam systems: Impact and pressure surges in steam piping, often caused by moving condensate or rapid condensation. It shares the name but involves steam-system mechanisms distinct from liquid-water surges.
Acoustic impedance: A measure of how strongly a medium resists oscillatory flow, determined by pressure and particle velocity. It helps determine how pressure waves reflect at changes in pipe material or geometry.
Slow-closing valve: A valve designed to reduce flow gradually rather than stop it abruptly. Slower closure reduces the velocity change that initiates a surge.

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