Q–The water pipes in my new home are driving me crazy. Every time the toilet or washing machine shuts off, there is a loud bang. The noise can happen at faucets but is reduced if I shut the water off very slowly. What is happening? Can this problem be solved? Is it expensive to fix?
A–You are a victim of water hammer. The source of the problem is abnormally high water pressure in your water system. My guess is that your existing water pressure is 115 pounds per square inch (PSI) or higher. I’ll bet you live at the bottom of a hill or near the lowest point of your municipal water system. The volume and weight of the water resting in the water mains above your house creates this high pressure. Some places in my city have main pressures that commonly exceed 150 PSI.
High water pressure is wonderful for hosing down driveways or powering lawn sprinklers. However, it wreaks havoc with faucets, valves and water heater pressure valves. The hammering noise within your pipes is created when the water flow is stopped abruptly. The average house has about 75 pounds of water within the piping system. When you rapidly shut off water to a fixture, the weight of the water crashes against the faucet, valve or sidewalls of the pipe. This creates the vibration and noise within the pipes you have been hearing.
The problem is easily solved by installing a pressure-reducing valve in your water system. These valves have a handy adjustable screw that allows you to adjust the pressure on the house side of the water system. Factory settings are usually between 50 and 60 PSI. I happen to prefer a setting of 70 PSI, which allows you to take vigorous showers.
Installation of these valves is not too difficult. They require simple soldering skills. However, you will need to check with your local plumbing inspector before you proceed. Some states and municipalities will not permit an unlicensed person to cut into or make alterations to the public water supply system. Your household water lines are really part of the public system. Under certain conditions (when a water main breaks or a fire engine is pumping), water can actually flow from your house into the public water supply.
The cost of installing a pressure-reducing valve depends on how much extra piping work you decide to do. Remember that everything on the house side of the valve will operate at the lower pressure. If you want to maintain the high pressure for your outdoor hose faucets, you undoubtedly will have to install additional water lines from the high pressure side of the new valve.
If you are able to perform the work yourself, your cost will be minimal. If you must use a plumber, the cost can easily exceed $500 or more.
The installation of a pressure-reducing valve can sometimes cause problems with a hot-water heater. Certain pressure-reducing valves contain a bypass that allows water to flow back into the municipal system and this bypass can malfunction.
When cold water enters your hot water heater and is subsequently heated, the volume of the water increases. Before the pressure-reducing valve was installed, this water actually was pushed back towards the street. If your new valve does not have a bypass or the bypass malfunctions, you can once again be troubled with water hammer.
It’s therefore wise to also install a simple expansion tank on top of the cold water inlet into the hot-water heater. This tank contains an air chamber that is separated from the water by a rubber bladder. The extra volume of heated water simply causes the bladder to expand within the tank. The expansion tank needs to be sized correctly. Just tell the plumbing supply house the capacity of your hot-water heater and it will know which size you need.
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Have questions about the remodeling process? Write to Tim Carter, c/o The Chicago Tribune, P.O. Box 36352, Cincinnati, Ohio 45236-0352. Questions will be answered only in the column.
For detailed instructions on installing pressure-reducing valves and hot water heater expansion tanks and other tips on reducing water hammer, send $2 and your name and address to Tim Carter at the above address. Ask for Builder Bulletin No. 187.
For a list of past Builder Bulletins and a wide variety of individual job bid sheets, send a business-size, stamped, self-addressed envelope to the same address.
Ask the Contractor can also be accessed via the Internet at http://www.chicago.tribune.com/homes/articles/askcon.
