Water Hammer
Water hammer is a pressure surge caused when a moving column of liquid is suddenly stopped or redirected, such as by a rapidly closing valve. The shock wave can rattle pipework, damage fittings and rupture lines.
When flow is halted abruptly, the liquid's momentum has nowhere to go, so its kinetic energy converts to a high-pressure wave that travels back through the pipe at the speed of sound in the fluid. The resulting bang can far exceed normal operating pressure. Mitigation includes slow-closing valves, air chambers, surge tanks and proper steam-trap drainage, since condensate slugs propelled by steam are a common cause in steam systems.