Water Hammer

Water hammer occurs when flowing water is abruptly halted—typically by a fast-closing solenoid valve, check valve, or fixture shutoff—and the momentum of the moving water column creates a shock wave that reverberates through the piping system. This shock can reach hundreds of PSI in an instant and produces the characteristic loud bang or series of bangs.

The problem gets worse on long runs of pipe, high water pressure (above 80 PSI), and with quick-closing devices like washing machine inlet valves or dishwasher solenoids. Over time, repeated hammer can crack fittings, rupture seals, and loosen connections. You'll hear it most often immediately after someone shuts off a faucet hard or when an appliance cycle ends.

The fix depends on the cause. Install water hammer arrestors (air-charged or spring-loaded devices) near the offending valve or fixture to absorb the shock. If the whole system is prone to hammer, a whole-house arrestor on the main line helps. Reducing system pressure, installing slow-close valves, or ensuring proper pipe support can also mitigate the problem. Code often requires arrestors on washing machine and dishwasher supplies.