July 24, 2008
Banging, Vibrating Water Pipes
Q. My water pipes sound like they're going to vibrate right out of the walls. I turn on the faucet in my bathtub, and the pipes behind the walls go "bang, bang." What's the problem and how do I solve it?
-Pam R., Huntington
A. The problem is called water hammer, and it can often be a difficult thing to correct. Here's what's happening when you hear that "bang, bang" behind the wall:
The water pressure in the supply lines of a residential home should be about 70 pounds per square inch (psi). In the case of water hammer, the pressure is too high, maybe more than 100 psi. This high pressure is great for running the inground sprinkling system, hosing suds off the family van and for pulsating showers, but it can reduce the life of your faucets and any of the valves in the home plumbing system. The banging is caused when the flow of this highly pressurized water is stopped or started abruptly.
You have a couple of alternatives: There are water-surge shock absorbers that can be installed on the supply line, or you can try to reduce the pressure near the faucet causing the water hammer by increasing the diameter of the supply pipe closest to the faucet.
If you choose to install "shock absorbers," you'll need one on the cold-water supply and another on the hot-water supply. They run about $11 each. I found one called Quiet Pipes made by Oatey (www.oatey.com; 800-321-9532), a Cleveland-based plumbing specialty company, at an area home center. This device must be attached to a half-inch female threaded tee, so you'll have to cut the existing pipes and solder the tee into place. The Quiet Pipes device then screws into the tee. The best place to install this for water hammer on a tub faucet is probably in the basement before the supply line reaches the flooring, or on the supply line near the faucet. You might have an access panel to the faucet pipes in a closet on the other side of the wall. (Step-by-step installation instructions are on the package.)
If you choose to increase the diameter of the supply pipe to the faucet, you'll also have to sweat pipe. In your case, your tub faucet is probably fed by half-inch pipe. If you can locate the feeder pipes to the faucet in the basement, change as much of each pipe as you can get to -- hot and cold water -- to 3/4 inch pipe. This likely will reduce the pressure considerably and could eliminate the water hammer. To do this, you'll need a run of 3/4-inch copper pipe and four couplings that will allow you to connect half-inch pipe to 3/4-inch pipe.
To do both these jobs, you'll have to be able to sweat copper pipe. It's not that difficult a task. (For a refresher on sweating pipe, read my column from Sept. 23, 1999.)
Water hammer often occurs near the supply pipes for washing machines. Activating a washing machine can cause quite a bit of pressure in the supply lines. If this is your problem, Oatey makes a special water-surge shock absorber that fits on the faucets that supply the washing machine. No sweating of pipe is necessary. These also cost $11 each.
I've heard of one more corrective measure, but I'd try it only as a last resort. There are pressure-reducing valves that can be installed near the shutoff valve for your water supply. But these valves change the pressure in your entire system, so the exterior hoses and the sprinklers won't operate with the same high-pressure efficiency after the valve is installed. In addition, the valves must be set correctly and they can wear out.
Plus, these valves can cause problems with water heaters. If the bypass on a pressure-reducing valve malfunctions, the pressure in your hot water heater can be affected and you can have water hammer problems again. To guard against this, an expansion tank can be installed on the cold-water inlet of your water heater.
If you have to resort to a pressure-reducing valve, by all means have a qualified plumber install it.
Copyright © 2008, Newsday Inc.
