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Water hammer is the term used to describe loud, banging noises in your pipes. It is caused when the water that has built up momentum flowing through the pipes is suddenly stopped by a rapidly closing valve. When water hits a sudden wall, it does not compress; it lashes back in a wave. This causes a severe spike in pressure (about 600 psi). Because of these hydraulic pressure spikes, water hammer can loosen pipes and damage fittings. This potential damage means that you will want to fix water hammer quickly. In this article, you will learn more about what a water hammer arrestor is and how to install it.

How to Cushion the Water

Air does compress; if there is a chamber full of air into which the water can go, the air will compress, and the water will have space not to shock. Often houses have air chambers in the plumbing to allow for this, but these fill with water and lose air over time and become ineffective.

You can try to refill them with air by completely draining your entire house’s plumbing system of water, then turning off the lowest faucet and refilling the system. As water moves up through the house, the chambers should stay full of air. However, these chambers do not work for long, as they immediately start filling with water/losing air again.

Fortunately, water hammer is still not at all difficult to fix. There is a small plumbing fixture you can add to your pipes called a water hammer arrestor. A water hammer arrestor stops (arrests) the noises by cushioning the water with air. Water hammer arrestors are fairly easy to install, relatively inexpensive, and quite effective in stopping water hammer. They are designed to keep their air cushion so that they will keep your water safely contained when it hits a sudden stop.

Installing the Water Hammer Arrestor – 8 Steps

a simple metallic water hammer arrestor

Step One – Locate the Problem

Identify the fixture that is causing the noise. Washing machines and dishwashers are frequent causes of water hammer because as they work, they start and stop the water suddenly and frequently, but any plumbing fixture could be the culprit.

Step Two – Collect Your Supplies

You will need a water hammer the right diameter for your pipes – two, if there is both a hot and a cold pipe going to the appliance, an adjustable wrench, a pipe wrench, pliers, and materials for either soldering copper or cutting and joining plastic pipe, depending on your plumbing. It’s also helpful to have a bucket to catch any water that didn’t drain, and towels or paper towels to clean up drips.

The best location for the water hammer arrestor is within six feet of the valve that is causing the pressure wave, so you are going to install the water hammer arrestor in the same room as the noisy valve.

Step Three – Access the Plumbing

Expose the plumbing fixtures for the appliance that is causing the noise. This could mean opening an access panel, pulling the washing machine or dishwasher away from the wall, or (if your plumbing is closed in behind walls) making a hole to access the pipes. Most likely, the valve beside which you need to install the water hammer arrestor is going to be readily accessible.

Step Four – Turn Off the Water

Turn off the water and drain the pipes; if you can’t turn off water to just that room, turn off the water to the whole house. You can drain the pipes by opening faucets, especially at the fixture on which you are working; the water will run out, and since there is no more coming in, they will be empty.

Step Five – Cut the Pipe

Cut the pipe. You will need to choose your location according to your plumbing set up. It needs to be beside the correct appliance; if the washing machine is the cause, adding it to the bathtub won’t do much good even if they are in the same room. You might be very close to the valve, or further if that is where the access is; be within 6 feet or less. Have your bucket ready to catch any water that runs out. Once the water is drained, you will cut out about a one-inch section of the pipe; the section cut out should be the right size for the water hammer arrestor fitting.

Step Six – Prepare the Pipes

If you have copper pipes, adjust the ends of the tubes, the t-fitting for the water hammer arrestor, and the arrestor by sanding and polishing them smooth and coating with flux. If you have plastic pipes, sand off any burrs, clean them very well and prepare according to your contact cement instructions.

Step Seven – Install the Water Hammer Arrestor

Connect the pipes to the t-pipe to which the water hammer arrestor will be connected. Connect water hammer arrestor to the t-pipe. Solder together (remember your safety goggles) if you have copper pipes; apply primer and contact cement as directed for plastic pipes. Repeat for the other side, if your appliance has a second water pipe.

Step Eight – Test the Water Hammer Arrestor

Allow the connection to cool or cement to dry before turning the water back on. Test the water hammer arrestor by having the appliance do whatever was causing the noise in the first place. While you are doing this, check carefully for leaks.

Other Related Issues

Water hammer can also be exacerbated by loose pipes, and can, in turn, make loose pipes worse. Loose pipes can also make loud noises. As part of evaluating the problem, you will want to check your pipes. If your pipes seem to be loose, tighten them up and add some pipe straps. It could minimize the problem and will add protection to your plumbing. You will also want to check the water pressure; pressure above 75 PSI can cause water hammer. If the water pressure is too high, replace or install a pressure regulator.

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