What is Water Hammer and Why is it Important That You Prevent it?

Posted by bloger 06/20/2016 1 Comment(s)

What is Water Hammer and Why is it Important That You Prevent it?

water hammer arrestor scheme of workingTalking to customers for more than forty three years, has taught me that it isn’t enough to clearly explain plumbing dangers. I have to convince people to take the necessary steps to prevent dangers.

Most people get alarmed when they hear banging noises in their pipes but find it difficult to believe they have a problem when everything sounds normal.


People don’t hesitate to spend money to make their pipes quiet. In this article, I hope I can convince you to be alarmed if there are no water hammer arrestors (shock absorbers) on the supply hoses to your clothes washer. Silent water hammer is worse than noisy hammering.


If there are no shock-absorbers (water hammer arrestors) on the clothes washer shut-off valves, there is a water hammer each time the washing-machine solenoid (fill valves) stop water flow (whether you hear it or not). This shock wave frequently causes premature plumbing failure.


My most effective way to explain what water hammer is:

When fast flowing water stops quickly, the energy of the flowing water quickly bounces back throughout the plumbing system. This shockwave creates a hammering effect in the water supply system in the home. Usually, if there are any loose pipes or any loose parts in the water supply system, banging (hammering) will be heard when uncontrolled shock waves travel from a fast closing valve. Unfortunately, uncontrolled shock waves can also create loose pipes and loose parts.

Water hammering and added stress contribute to premature failure. Fill valves on toilets, faucets, solenoid valves, pressure reducer valves, and other water control devices are exposed to a very stressful shock each time energy bounces back uncontrolled from a fast closing valve.

Shock absorbers (water hammer arrestors) installed close to fast closing valves, provide trapped air that absorbs the bounce back energy flowing back from the valve. Much like the shock absorbers on a car absorb energy traveling up from sudden impact, water hammer arresters capture the energy flowing back from a fast closing valve.

Capturing bounce back energy also helps to protect supply connections, pipes and water heaters. Water hammer seems to increase risk of premature plastic pipe failure, supply line failure to toilets and faucets and other connection failures. I also think hammering increases the frequency of pinhole leaks in copper water pipe. I think water hammering contributes to water heater heat trap problems, safety valve leaks and could even contribute to premature water heater failure.


Top quality plumbers, many years ago, used to make water hammering arrestors out of short pipes and caps. The problem with those type arrestors is that eventually, they would get water logged. Modern water hammer arrestors use rubber to separate the shock absorbing trapped air from water. Water hammer has always been around, now, better, easy to install arrestors have replaced capped pipes.  

If you need more convincing you can buy a pressure gauge with a hose connection and make some observations when your clothes washer solenoid valve closes. Usually it will be easy to see dramatic needle jumps on a pressure gauge even if it is attached on an outside faucet located far from the clothes washer.


Of course, the higher your water pressure is, the more dangerous the water hammering will be and the more it is likely that you will hear it. Some people stop noise by replacing a defective pressure reducer but fail to realize that the useful life of the new pressure reducer will be shortened by the silent-but-still present water hammering.

Much in the same way high blood pressure can be “the silent killer”, high water pressure and/or water hammer can cause major damage.


Homes that rely on a pressure reducer to control high water pressure coming in from municipal water mains must make sure the pressure reducer is working properly. Pressure reducers and other causes can also create banging and other strange noise.

It is important to make sure shock-absorbers are at least installed on the shut off valves for the clothes washer.

It is best to have a shock-absorber on every fast closing valve. They are recommended and are available for clothes washers, dish washers, ice makers and even toilets.

Most home owners are probably capable of installing shock-absorbers on clothes washer valves if they are capable of replacing their clothes washer hoses. Special, extremely easy to install water hammer arrestors usually only require one additional hose type connection.

I always strongly recommend people find a trustworthy plumber to do all plumbing. If you are determined to install your own water hammer arrestors for a clothes washing machine, I hope you will read my “Warnings and Tips Concerning Clothes Washer Supply Lines” article.  

I hope the communication skills I learned talking to customers and other plumbers for over forty three years will help you. If I can convince you to make smart decisions, I have done my job.

By Mike Quick / MikeQuick.com