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Fri, Nov. 22

Ask the contractor: It’s not a jackhammer, it’s a water hammer

Loud banging in pipes may mean that it needs air added to cushion water after its shut off. (Metro Creative Graphics)

Loud banging in pipes may mean that it needs air added to cushion water after its shut off. (Metro Creative Graphics)

Help, we have “jackhammer” noise inside our walls. What is going on?

— Ed and Nancy, Prescott

Most likely you have a water hammer condition. A water hammer is a specific plumbing noise and not a generic clanking and clinking and pipe clatter sound. It occurs when you shut off the water suddenly and the fast-moving water rushing through the pipe is forced to stop or change direction, creating a sort of shock wave and a hammering noise.

Water hammer is the sound of moving water being suddenly stopped cold by the closing of a valve. Think of running full speed and suddenly running into a brick wall. The force, or inertia, of this water is transferred instantly from the water to the pipe, and then into the fixtures or framing of your home. Hard to ignore, this hammer-like sound can be heard throughout all your plumbing.

Plumbing systems have air chambers, or cushions, that compress when the shock wave hits, softening the blow and preventing this hammering. These chambers can fail in time because water under pressure gradually absorbs the air.

If you never had hammering and then it suddenly starts, most likely your plumbing system’s air chambers have become waterlogged. You can cure water hammer by turning off the water behind the waterlogged chamber, opening the offending faucet and permitting the faucet to drain thoroughly.

Once all the water drains from the chamber, air will fill it again and restore the cushion. If the air chamber is located below the outlet, you may have to drain the main supply lines to allow the chamber to fill with air again. Don’t panic, but this pressure wave can cause major problems, from noise and vibration to pipe collapse. Water hammers can cause pipelines to break if the pressure is high enough.

In the home, water hammers may occur when a dishwasher, washing machine, or toilet shuts off water flow, because these devices use quick-acting solenoid shutoff valves. The result is hearing loud banging or repetitive banging. It would be best to contact a plumber to have them check the water hammer and they can be eliminated. However, water hammers can and do occur with toilet valves and plain old faucets as well.

Water hammers can be stopped — the hammer is controlled by the installation of either permanent air chambers, water hammer arrestors, or both. The permanent air chamber is simply a vertical section of copper pipe with a cap on the end that is attached with a T-fitting to the supply line near a shutoff valve or appliance. They are installed on both hot and cold water lines. The chamber is filled with air which absorbs the force of the moving water by compressing within the chamber, acting like a shock absorber.

The three culprits causing water hammers are first the length of the pipe the water is traveling through. You can’t do much about the length of your pipes, assuming that you can’t move your house closer to the water source. But it is an important factor in creating water hammers, so it is useful to take a look at it, especially as it relates to the pipe size.

The second variable is time, or specifically how fast the water is being stopped. When a closing valve is causing water hammer, time is how long it takes for the valve to close.

The third factor that influences water hammers are the velocity of the water. The faster the water is traveling in the pipe, the greater the water hammer. It is this last factor which is easiest to correct.

Sandy Griffis is executive director of the Yavapai County Contractors Association. Email your questions to her at or call 928-778-0040.

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