Water Hammer Arrestors

DEAR MIKE: Every time I turn off the water faucet in my laundry room, it sounds like someone is banging on the wall. Is my house possessed by evil spirits? Please help, the noise is frightening my kids. -- Cathy B.

DEAR CATHY: I'm going to banish these noisy ghouls from your house, and I'm bringing along my water hammer.

Actually, water hammer (commonly referred to as "banging pipes") is the problem, and occurs when a water fixture is closed suddenly, sending a shock wave through the pipes. This shock wave will travel back and forth until its energy is used up.

A shock wave can also be caused by a person slamming down a faucet handle, like a single-handle kitchen faucet. But most often it's caused by electric solenoid valves, such as those found in dishwashers and washing machines. These valves stop the flow of water very quickly, creating the shock wave.

Water hammer can also sound like the pipes are vibrating, leading people to believe that the pipes are loose inside the wall. This may be, however, water hammer can occur even if the pipes are securely fastened. If not, the noise would be much worse -- imagine the sound you'd hear when the shock wave knocks loose pipes against the framing of the house.

Water hammer can be prevented by installing a water hammer arrestor (about $10). It acts like a shock absorber by allowing the shock wave to dissipate in its air chamber.

A water hammer arrestor is roughly 8 inches long and has a cylinder about the diameter of a dime. Inside the cylinder is an air chamber, where the shock wave's energy is absorbed. A diaphragm separates the air chamber from the water in the pipes.

The arrestor should be installed as closely as possible to the source. There are arrestors designed for other areas in the home, but because you've isolated the problem to the laundry room, these screw-on gadgets that I mentioned will be just what the doctor ordered.

You can install an arrestor on your washing machine in about five minutes. Actually, you'll need two arrestors -- one for the hot water and one for the cold. The fittings are threaded, so it's simply a matter of screwing them into the system.

First, turn off the hot and cold water valves in the laundry room. Unscrew the washing machine's hoses where they connect to the water valves, then screw an arrestor onto each valve. Screw the hoses onto the arrestor fittings, then turn the water back on. If it leaks, give it another one-eighth turn. It's that easy.

Once the fix is made, your kids will no longer be scared by things that go bump in the night. 

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