Water hammer arresters are engineered devices used in plumbing water supply systems to absorb and mitigate pressure surges caused by the sudden stoppage of flowing water – or water hammer. Water hammer is not a hammer made of water, but occurs when a valve closes quickly, creating a shock wave that travels through the piping. This shock wave can result in noise, vibration, and potential damage to pipes, valves, and appliances. Water hammer arresters control this effect by providing a measured cushion of air, which is permanently separated from the water. The air cushion is compressed under the pressure surge and dissipates the energy. Arresters are typically installed near quick-closing valves or appliances that use solenoid valves, like washing machines, dishwashers, and ice makers. Water hammer arresters are often required by plumbing codes in applications where water hammer can occur.