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Easy to stop water hammer - BANG!

Dear Ms. Builder: We have a new house and when the clothes washer or a faucet shuts off, there often, but not always, is a loud knock. It is really annoying at night. What is it and how can I fix it? - Pat N.

Dear Pat: The noise that you hear sounds just like its name - water hammer. Excessively high water pressure, along with the plumbing design (or lack of it) in your house is the problem. You most likely live at the bottom of a big hill or in one of the lowest areas in your community.

In low elevation areas, the supply water tower is much higher than your house. The greater the elevation difference between the water tower and your house, the higher the water pressure. It can get as high as 120 psi (pounds per square inch). I prefer a water pressure of about 60 psi.

When the pressure is too high and the water is on full force, like when washing clothes or flushing a toilet, it is flowing through the pipes very fast. When it is quickly shut off and the flow stops almost instantly, this creates a shock wave that you hear as water hammer - a loud BANG!!

Although your house is already completed, the plumber should have installed 3/4-inch pipes as much as possible throughout your house. My guess is that your plumber used only 1/2-in pipes and did not consider your high-pressure location. With a larger pipe, the speed of the water is reduced.

Don't fret though. There are still two things you can do in combination to get a good night's sleep even if the kids flush a toilet. You will have to 1) install a pressure-reducing valve and 2) install an expansion tank. If you can solder a copper pipe, this is not a difficult job for most do-it-yourselfers. Check your local plumbing codes.

A pressure-reducing valve is a simple device that has a screw to adjust the water pressure to any psi setting you want. It is usually installed immediately where the water main enters your house. If you still want high pressure at an outdoor faucet for washing your car, install it after that branch.

Some plumbers recommend installing a pressure gauge along with a pressure-reducing valve. In order to save some money, I skip the gauges and just adjust it for enough pressure to rinse my hair in the shower. If you still hear water hammer, adjust the screw in a little further.

Many pressure-reducing valves can block the flow of water back into the main water inlet. This can create a problem because, as the water temperature in your water heater varies throughout the day, the water expands and contracts.

If the pressure-reducing valve blocks the water flow back into the main, this expanding water has no place to go. The water pressure buildup can cause faucets and the water heater pressure and temperature safety valve to leak. This is not a good situation.

Solving this problem is simple too. Just install an inexpensive expansion tank in the cold water side of the water heater. This is a small tank, like a propane gas tank, that has a flexible bladder inside. If the hot water expands, the excess goes into this tank, so there are no leaks or problems.

To install a pressure-reducing valve, shut off the water to your house. Remove a section of pipe long enough for the pressure-reducing valve and an isolation valve on either side of it. Solder the valves into the line and adjust the pressure. The expansion tank is mounted on a tee in the cold line.

Tools and materials required - tubing cutter, propane torch, two isolation valves, pressure-reducing valve, expansion tank, copper tee, sandpaper, wire brush, solder, flux

Send your questions to Ms. Builder, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com/msbuilder.