Water Hammer Arresters

Water hammer arresters (also spelled “water hammer arrestors“) are used to stop the inertia caused by a sudden stop in the flow of water. Have you ever heard a load banging noise when you turn off your water or when the toilet is done filling up? If so, you are hearing what is known as “water hammer“.

Water hammer is the noise that is the result of fast moving water suddenly coming to a stop. When the water is suddenly stopped by shutting off a valve, the inertia causes the plumbing to bang up against a wall, stud or other plumbing. The noise from water hammer can be very load and will reverberate throughout your entire plumbing system and can often be heard throughout the entire home.

A lot of people don’t know that there are devices made specifically to prevent this phenomenon. They are called water hammer arrestors. The name was purposely misspelled in the title because that is what people on this site have been searching for, but the correct spelling will be used throughout the rest of the article for the sake of correctness.

Potential Damage due to Water Hammer

The noise itself may not bother everyone, but surely the damaged caused by the noise will. As the water travels through your pipes, it gains inertia. By the time the water hit’s the end of its course, the shut off valve, it has gained enough inertia to slam the entire pipe up against the inner side of the wall, joists or other pipes.

This action will eventually cause the brackets that hold the pipes in place to weaken and come loose so that the movement increases. Then, the constantly banging pipes will cause the soldered joints to come loose and leaks will eventually appear. So, while the noise may not be so bad to some, the damage that the noise represents should be enough to convince every home owner into wanting to stop it.

Luckily, there is a device to stop water hammer. It is called a water hammer arrestor. A water hammer arrestor is specially designed to absorb the excess inertia caused by the sudden cut off of the water’s flow.

A water hammer arrestor is basically a sleeve with a piston in it. They are attached to the pipes and when the water enters the sleeve after a valve has been closed, the water hit’s the piston. The piston absorbs the shock slowly so that the pipe doesn’t slam up against the wall or other plumbing. That in affect stops the annoying water hammer noise and the water hammer damage.


Price is always a concern when adding on to your plumbing. Not to worry, water hammer arrestors don’t have to cost an arm and a leg. You can get simple models for right around $20. Installation may be another matter.

If you have any plumbing experience, you can probably do it yourself as they are not any harder to install than a regular section of pipe. If you have to hire someone to do it, it could get a bit pricey depending on where they need to be and how many are necessary.

Stopping Water Hammer

There are other steps to stopping water hammer as well. Unfortunately it is not just as simple as installing a water hammer arrestor, although the will help. Before you start any work, you should inspect your plumbing carefully.

Go into the basement or wherever your plumbing is run, and watch all the pipes for movement while someone else flushes the toilet and turns faucets on and off repeatedly. Generally, where you see movement, you are likely to find loose mounting brackets and/or leaks.

Also inspect the rest of the mounting brackets and joints jus t to be sure. Besides water hammer arrestors, there is another trick that plumbers use to stop the movement of pipes. It is known as an air chamber.

Do it Yourself Air Chamber

An air chamber is simply a vertical copper pipe attached to the plumbing with a T-fitting. It has a cap on the top and is attached to the plumbing at the bottom. The idea is for this chamber to remain full of air and it will act very similar to the water hammer arrestor accept that instead of compressing a piston, it compresses air. Most homes should have them built in.

But, some homes don’t have them and the ones that do have problems. Air chambers will lose their air over time and it becomes necessary to drain the entire pipe system to replace the air in them. They can also become blocked.

Because built in air chambers are usually inside a wall, they are not easily fixed. So, here we will quickly describe how you can make a new one if you don’t feel like tearing apart a wall and/or draining all of your pipes.

The air chamber we describe here will fit behind a normal toilet since toilets are one of the most common causes of water hammer. This device will usually absorb any water hammer caused by a toilet. It is as described earlier, simply a vertical copper pipe added on to the existing plumbing. In this case we will be adding it onto the pipe leading to the shut off valve in back of the toilet.

You will need a decent size length of 3/8 inch copper tubing. The longer the vertical pipe, the better it works. You can even zigzag your “vertical” pipe behind the toilet tank if you want, but a length of pipe that nearly reaches the top of the toilet’s tank is sufficient in most cases. Then you will need a T-fitting to attach the vertical pipe to the pipe just before the shut off valve behind the toilet.

After that all you should need is to cap off the top and of the pipe. Make sure all of your fittings and the end cap are extremely tight and do not leak at all. The slightest leak will cause the air chamber to fill with water and leak.

Different toilets may require slightly different parts to do the job. That is why we don’t go into great detail here. What you need to do is inspect the back of your toilet and take some notes regarding the size of the fittings, shut off valve, etc. and go to your local plumbing supply store and explain what you want to do and they will be able to help you get the proper parts to do the job for your individual toilet assembly.