Water Hammer Arrestors: Why Pipes Bang and What the Fix Does
Water Hammer Arrestors: Why Pipes Bang and What the Fix Does
A loud bang in the walls when a faucet or washing machine valve shuts is usually water hammer. This guide summarizes what two manufacturer pages say about the cause and the device used to cushion it.
What water hammer is
Per Oatey, water hammer occurs when water flow is suddenly stopped or redirected, for example when a faucet is closed abruptly. The page says water at about 60 to 70 psi carries energy that has to go somewhere. Left untreated, it can range from an annoyance to serious damage, including joints blowing apart and water damage. Sioux Chief (via PexUniverse) names rapid closing of a valve, especially quick-closing or quarter-turn valves, as the cause of the pressure spike.
How an arrestor works
An arrestor gives the shock somewhere to go. Oatey describes a piston in a sealed, pressurized, gas-filled chamber; the piston keeps water out of the chamber, and the units work at any angle. Sioux Chief describes an air chamber with a lubricated piston acting as a cushion.
Installation points from the sources
- Supply lines must be rigid and securely fastened so the energy reaches the arrestor (Oatey).
- Connection types listed include PEX, copper (sweat and press), CPVC, threaded and compression.
- Oatey lists size AA for residential use and sizes A through F for commercial use. The pages give no sizing method. Not verified: which size suits your fixtures; ask a plumber or check the maker's chart.
- Sioux Chief states UPC/IPC listing and ASSE certification. Its page also carries a lead notice that conflicts with its lead-free statements, so confirm with the manufacturer before using one on potable water. Not verified: lead-free status of that product line.
Other causes to check
High supply pressure can add to the problem. Not verified: whether your banging comes from hammer or from loose pipes; a plumber should diagnose it.
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General information only. Not plumbing, legal or code advice. Confirm with a licensed plumber and your local building department.