How to Reduce Water Hammer in a PVC Pipe

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It's easy to spot plumbing problems like leaks or low water pressure, but some issues are more subtle, or you might not be sure of what they are. Water hammer is one issue related to water pressure that's noisy but doesn't seem to disrupt your water flow. It can cause plumbing issues down the road, though, even in PVC pipes.

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What Is Water Hammer?

When you hear banging or vibrations in your plumbing, water hammer is likely the cause. Metal pipes typically make more clanging and banging with water hammer, but PVC pipes can also experience the vibrations. It happens when you shut off a faucet or when a valve shuts on an appliance, like your washing machine when it's finished filling. All of the pressure that was flowing through the pipe suddenly stops, creating a shock wave that travels back through the pipe to help disperse the pressure.

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Effects of Water Hammer

As the pressure travels back through the pipe, it causes vibrations that can make the pipes shake and sometimes bang into the wall or nearby structures. PVC pipes often experience expansion as they absorb the shock waves. While this doesn't usually affect the pipes, it can affect the various joints and fittings used to connect the plumbing. The damage can be especially hard on solvent weld fittings in your PVC plumbing.

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Installing Water Hammer Arrestors

Adding water hammer arrestors to your PVC pipes can help reduce the water hammer effects. This simple device sticks out from the pipe and has air inside. When a valve shuts off and the pressure increases, water moves into the water hammer arrestor and compresses the air cushion to release the pressure.

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Install the arrestors on hot and cold water supply lines. You can add them near your washing machine, refrigerator ice maker, dishwasher, and bathtubs to prevent water hammer when using those appliances and fixtures. If you have a residential irrigation system, it can also be a major source of water hammer and should have an arrestor installed. There are different types of arrestors for different water lines, including devices for your laundry connections and showers. The ideal location is no more than 6 feet away from the valve for each item.

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Ensure you choose water hammer arrestors that are compatible with PVC plumbing. Sioux Chief and SharkBite are two manufacturers that make water hammer arrestors for different types of plumbing, including PEX and PVC.

How to Install an Arrestor

Water hammer arrestors are often installed near appliances or plumbing fixtures. An arrestor placed on the supply lines to those fixtures prevents water hammer vibrations from traveling back into the PVC pipes. The steps to install a water hammer arrestor can vary depending on where you install it:

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  1. Shut off the water supply to the appliance or fixture. Turn on a nearby faucet to release water pressure and empty the pipes.
  2. Unscrew the supply line from the stop valve.
  3. Screw the water hammer arrestor onto the valve.
  4. Reconnect your water supply line to your water hammer arrestor by screwing it onto the end. Hand-tighten the connection and use a wrench to tighten the connection another one-fourth turn.
  5. Open the stop valve and turn on the water.
  6. Check for leaks at the connection.

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Adjusting Water Pressure

Another possible way to minimize water hammer is by lowering the water pressure to your home. However, this option should only be used if the water pressure is too high. Lowering it too low can cause poor performance in your plumbing fixtures. You can check your water pressure and make changes to the water pressure regulator if needed.

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Residential water pressure shouldn't be below 40 psi or above 80 psi. Anything above 80 psi can cause major damage to your plumbing. If your water pressure is on the high end, you can either have a water pressure regulator installed if you don't have one or adjust the one you already have.

The water pressure regulator adjustments are relatively easy. You'll need to grab an adjustable wrench to loosen the locknut. Lower the pressure of the water by turning the adjustment screw counterclockwise. Avoid making major adjustments, as you can quickly drop the pressure too low.

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