Water hammer is a pressure wave created when moving water stops very quickly, such as when a washing-machine solenoid valve closes. It is recognized by a bang that coincides with shutoff; prevention involves valve-closing behavior, pressure, and absorbing the pressure wave rather than randomly fastening pipes.
Confirm that the bang happens exactly at shutoff
An immediate bang when a fast valve closes or an appliance finishes filling fits water hammer. Noises that occur as pipes heat up or during steady flow may have a different cause.
Check whether household water pressure is excessive
High pressure increases the energy of the wave and wear on fixtures and valves. Measure with an appropriate gauge or have it checked; do not adjust a pressure-reducing valve without knowing the target and procedure.
A hammer arrestor works best near the fast-closing valve
Washing machines, dishwashers, and other solenoid valves can benefit from a properly sized arrestor installed for that branch. Do not substitute an improvised air chamber without understanding plumbing requirements and maintenance.
Loose pipes can amplify the noise without causing the pressure wave
A moderate pressure wave can make an unsupported pipe strike framing or metal. Correct accessible supports without crushing pipe or approaching wiring; when banging is widespread, investigate water pressure and the hydraulic cause first.
Sources
- U.S. Environmental Protection Agency WaterSense — Home Maintenance — Household maintenance related to water, leaks, and efficient use.