Water hammer: Characterized by a sound that resembles the sound produced when
a pipe is “hammered.” This occurs when a liquid in a piping network encounters an
abrupt flow restriction (such as a closing valve) and is locally compressed.
The acoustic waves that are produced strike the pipe surfaces, bends, and valves as
they propagate and reflect along the pipe, causing the pipe to vibrate and produce
the familiar sound.
Water hammering can be quite destructive, leading to leaks or even structural
damage. The effect can be suppressed with a water hammer arrestor.