During pressure testing, which practice helps prevent water hammer?

• A. Quickly closing valves to depressurize quickly
• B. Slow-closing valves, air chambers, or proper pressure relief
• C. Increasing testing pressure gradually without relief
• D. Vent all water to atmosphere before testing

Answer: (B)

Water hammer happens when a moving stream of water is suddenly stopped or redirected, causing a pressure surge that can damage pipes and fittings during a pressure test. The best way to prevent this is to use valves that close slowly so the flow is decelerated gradually, and to include devices like air chambers or modern water-hammer arrestors that cushion the surge by absorbing the extra pressure. A proper pressure relief mechanism also helps by preventing pressure from spiking beyond safe levels during testing. Together, these practices keep the pressure changes gentle and protect the system from shock. Quick valve closures or venting all water to atmosphere can create or fail to control sudden surges, increasing the risk of damage rather than preventing it.