What Is a Water Hammer Arrestor?
A small sealed air chamber on a supply line that soaks up the pressure spike when a valve slams shut, which stops pipes from banging.
A short fitting with a piston and a sealed pocket of air or gas that sits on a water line near a fast-closing valve, such as the one in a dishwasher or washing machine. When the valve shuts and the moving water stops suddenly, the piston compresses the air and absorbs the shock instead of sending it through the pipes as a bang. Screw-on versions fit between the supply hose and the appliance, and cost $10 to $20.
Size them by the fixture and the thread: appliance versions use a 3/4 inch hose thread, and faucet versions use 3/8 inch. Old houses relied on air-filled vertical pipes behind the wall to do the same job, and those fill with water over the years, which is why draining the system sometimes restores quiet.
Fixes that use this
Bathroom
How to Fix Banging Water Pipes (Water Hammer) in One Evening
A bang when a faucet shuts off is water hammer. Check pressure, strap loose pipes, and fit a $15 arrestor on the noisy fixture. Most fixes are under $40.
Time30–90 min Cost$5–$60 moderate
Related terms
Flapper Fill valve Shutoff valve Pressure regulator Supply line