Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). Water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It's also called hydraulic shock.
This pressure wave can cause major problems, from noise and vibration to pipe collapse. It is possible to reduce the effects of the water hammer pulses with accumulators and other features.
Rough calculations can be made either using the Joukowsky equation, or more accurate ones using the method of characteristics.
Read more about Water Hammer: Cause and Effect, Water Hammer During An Explosion, Mitigating Measures, The Magnitude of The Pulse, Expression For The Excess Pressure Due To Water Hammer, Dynamic Equations, Column Separation, Simulation Software, Applications
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—Henry Wadsworth Longfellow (1807–1882)
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—Lyndon Baines Johnson (1908–1973)