A water hammer arrestor is a small cylindrical device containing pressurized air or gas that absorbs pressure spikes from rapid water deceleration in pipes. It acts as a cushion, preventing the shock waves and banging sounds characteristic of water hammer.
Technical Details
Arrestors contain a sealed chamber with compressed air separated from water by an internal diaphragm or piston. When pressure spikes occur, the air chamber compresses, absorbing excess pressure energy. Standard residential arrestors measure 2 to 4 inches long and 1 to 1.5 inches in diameter. They connect in-line or at fixture supply points using 1/2-inch or 3/4-inch threaded connections. Typical air precharge is 40 to 60 PSI for systems operating at standard municipal water pressure.
Installation and Maintenance
Arrestors install vertically with the air chamber pointing upward to prevent water absorption. They require recharging every 5 years as air gradually dissolves into water. Building codes require arrestors on all quick-closing valves and behind washing machine hose connections.
Practical Significance
Proper installation reduces pipe stress and extends system life. One arrestor typically protects multiple fixtures within 12 feet of the installation point.