What is "water hammer"

Water hammer \Wa"ter ham"mer\ (Physics)

1. A vessel partly filled with water, exhausted of air, and hermetically sealed. When reversed or shaken, the water being unimpeded by air, strikes the sides in solid mass with a sound like that of a hammer.

2. A concussion, or blow, made by water in striking, as against the sides of a pipe or vessel containing it.

3. A metal hammer used when heated, as by dipping in hot water, to blister the skin, as for counterritation.

n. 1 (cx uncountable English) A surge of pressure in a pipe carrying a fluid; especially the banging sound in a steam or hot water pipe caused by bubbles of air, or by an abrupt alteration of the flow. 2 (cx countable historical English) A metal hammer used when heated, as by dipping in hot water, to blister the skin, as for counterirritation.

n. the banging sound of steam in pipes

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). A 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 is 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, expansion tanks, surge tanks, and other features.

Rough calculations can be made either using the Zhukovsky (romanised as Joukovsky or Joukowsky) equation, or more accurate ones using the method of characteristics.