"Water Hammer"

What is water hammer?

Water hammer occurs when the flow of moving water is suddenly stopped by a closing valve. This sudden stop causes the whole column of water behind the valve, and itself, like a freight train crashing into a wall. This tremendous spike in pressure is called water hammer, and it not only acts like a tiny explosion inside pipes, it can be just as destructive.

Water hammer is usually recognized by a banging noise that is heard when water valves are shut off, though water hammer doesn’t always make these telltale noises. 

How much damage can water hammer do?

Uncontrolled water hammer will accelerate the failure of water filters, valves, backflow preventers, washing machine hones, pipe fittings, etc.  On a water line of just 50 PSIG, it will commonly result in pressure spikes of 250 to 400 PSIG. This pressure spike is not at the valve; it reverberates backwards from the valve throughout the plumbing system, rattling and shaking pipes until it is absorbed.  

What types of valves can cause water hammer?

Any quick-closing valve can cause water hammer. In residential systems, these valves are typically found at the washing machine, the dishwasher, the tub/shower, and the icemaker at the refrigerator. Kitchen or lavatory faucets, toilet ball-cocks and lawn sprinkler systems can also create the problem. Water hammer can occur on both hot and cold water systems.

Where can I get a water hammer arrestor?

Any plumber can furnish and install a water arrestor.  Do-It-Yourself versions is available from your local home store.