Water hammer is the pressure caused when a fluid in motion is suddenly stopped or is made to change its direction. It is also known as hydraulic shock. Water hammer usually occurs when a valve closes at an end of a pipeline system. This pressure can cause a lot of serious problems, such as explosion or collapse of the pipe, and appendages due to loud sound, and vibration.
Water hammer can be experienced in domestic plumbing, in dishwashers, washing machines, and in toilets. It can also happen in hydroelectric generating stations. It can be heard as a loud banging, repetitive banging, or as some shuddering.
The effect of water hammer can be significantly reduced with the help of water hammer arrestors. Water hammer arrestors are hydro pneumatic devices similar in principle to a shock absorber. When installed between the water pipe and the machine, it absorbs the shock reduces pressure in the piping system to safe levels.