What is water hammer and how can it be prevented?

Water hammer is a pressure surge caused by sudden velocity changes in liquid flow, typically from valve closure or pump shutdown. Pressure rise is ΔP = ρ×c×ΔV, where c is wave speed (1000-1400 m/s in water). This can cause pipe rupture, joint failure, and equipment damage. Prevention methods: slow valve closure (closure time > 2L/c), surge tanks or accumulators, air chambers, pressure relief valves, controlled pump startup/shutdown using VFDs, non-return valves with dashpots, proper pipeline anchoring, and avoiding air pockets that can accelerate water columns.