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Hammering water pipes are cause of great annoyance

QuestionOur seven-year-old gas water heater makes popping noises every time water (hot or cold) is turned on, the toilet is flushed, the sprinklers come on, etc. What causes this?

AnswerIf you had said that popping noises occur every time you use hot water, then I would suggest that the noises come from the water tank. If that were the case, the annoying rumbling, popping, and banging noises you hear would be the pockets of water trapped between layers of sediment that turn to steam as the water heats.

The sediment, essentially mineral precipitates, forms an insulating barrier between the water and the surface of the tank bottom so the tank requires much more energy to heat water. Additionally, excess heat on the tank's bottom can lead to premature tank failure. These are two good reasons to minimize or eliminate sediment buildup.

However, because the noises occur with both cold and hot water, I believe you are experiencing water hammering or air trapped in the pipes. These noises are not associated with the water heater.

True water hammering occurs when the water flow is suddenly stopped. Suddenly turning off a shower faucet can send pressure, or shock, waves down the water line and through the water, shocking pipes and creating a "hammer" noise. Experts say that the shock wave travels faster then the speed of sound and creates enormous pressure within the pipe. Over time, it can damage pipes and valves and eventually weaken pipe joints.

Think of it as a train traveling through a tunnel at high speed suddenly slamming into a ton of rocks at the end of the tunnel. The back of the train, unable to stop, continues forward and collides with each rail car in front of it to the point of impact, creating one horrendous crash. Closing a valve suddenly is like blocking the end of the tunnel. The impact causes a big thumping noise followed by echoes in the pipe.

The real culprits are dishwashers and washing machines. Their solenoid fill valves can cause the hammer noise, and worn solenoid valves can cause a repeated hammering noise, similar to a machine gun. It is also possible that such appliances demand more water than the pipes supplying it can safely handle.

A simple solution might be to install water hammer arresters in a vertical position at the shutoff valves; purchase them at any home center or plumbing store. Another possibility is that the appliances may need larger pipes. During our remodel I installed 3/4-inch copper pipes along with arresters on both hot and cold water supplies at the shutoff valves and we haven't experienced any hammer noise.

Noisy pipes aren't always a sign of true water hammering. It is also possible that air is trapped in the pipes, causing a vibrating or ticking sound that can be more annoying than true water hammer.

Air trapped at high points of the pipe system can be very difficult to push out. Because air rises above water, find the high spot (often right after the water heater), cut the pipe (make sure the water is off and the system is drained), and install a tee with a 1/2-inch ball valve on the tee outlet so it points up. Install a 2-inch nipple between the tee and valve. Make sure the valve is closed when you turn the water back on; the air will rise to the highest point, i.e., to the upright 2-inch nipple. Then open the valve a little bit and let the air escape; be prepared because water will also squirt out. Finally, cap the end of the nipple when you're done so the valve will not leak if it is accidentally opened.

Copyright © 2005, 2006, & 2008 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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C.R.S., Inc. · Spokane, Washington · USA

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