When and How to Install a Water Hammer Arrester

Plumbing repairs
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Have you ever heard the pipes rattle or bang when the toilet fills and then suddenly stops. Or how about when the washing machine is done filling you hear a loud bang from the pipe. This pressure surge is called a water hammer. Water hammer is caused by the sudden stop or change in direction of water flow. This is very common in residential plumbing. In most cases, water hammer does not cause any damage to plumbing but it can be very annoying.

In some rare circumstances, water hammer can cause failure to fittings or pipes.

The first thing to do when you hear water hammer in your house is to check the water pressure. Often you will hear much more hammering and knocking noises when the household water pressure is too high. Test the water pressure with a gauge that can screw onto an exterior hose bib or behind the washing machine. If the pressure is above 75 psi then a pressure regulator should be installed or replaced if the existing one has gone bad. The pressure regulating valve should help maintain a safe and even water pressure and thereby prevent the water hammer.

It could be that the household water pressure is within the normal limits of pressure but you have recently installed a new washing machine, dishwasher, or ice maker line and this is causing a water hammer. If that is the case you can install a water hammer arrester at the source to stop the hammering.

There is a type of water hammer arrester that can fit onto an existing water shut off valve. Look for one of these at your home improvement or hardware store.

I recently installed a water hammer arrester on a washing machine water supply line because it was hammering badly every time the washer stopped filling.

First I checked to make sure the pressure to the house was not high. When I found that the pressure was normal I installed the water hammer arrester and it solved the problem.

Installing a Water Hammer Arrester on a Washing Machine

  1. Turn off the water at the washing machine valves. To effectively solve the problem make sure to install water hammer arresters on both the hot and cold water supply lines. Most likely both sides have the same pressure and both will require water hammer arresters since both hot and cold valves on the washing machine are built the same.
  2. Disconnect the washer hoses from the water supply valves. Take care that you do not lose the washers at the end of the hoses.
  3. Connect the water hammer arrester to each water supply valve. Check to make sure that there are washers in the swivel nuts before connecting the hammer arresters. The washers can easily fall out and the arrester will leak badly without one.
  4. Tighten the arresters onto the valve hand tight and then just a bit more with pliers so they are snug.
  5. Connect the washer hoses to the water hammer arresters taking care that you match up the hot water hose to the hot water supply. Once again make sure that the hose washers are in the swivel nuts.
  1. Turn the water back on and check for leaks. Tighten any joints that may be leaking just a bit more. The arresters will work at any angle so position them so they work for your situation.

Note: Most of the water hammer arresters I have seen are installed on the washing machine valves but the instructions may recommend connecting them directly to the back of the washing machine if possible because it protects the washer hoses as well. The problem with connecting the arrester to the back of the washing machine is that it can make the washing machine sit further away from the wall. If space is a tight connecting the arresters to the valves may be the only option.