What causes water hammer and how is it prevented?

Water hammer is a pressure surge caused by sudden velocity change - rapid valve closure, pump trip, or check valve slam. Pressure rise approximately dP = rho*c*dV, where c is acoustic velocity (1000-1400 m/s for water). Effects: noise, vibration, pipe rupture, equipment damage. Prevention: slow valve closure (5-10 pipe lengths travel time), surge relief valves, surge tanks or accumulators, flywheel on pumps (extends coastdown), soft-start/stop on pumps, and air chambers. Analysis using method of characteristics for critical systems.