What is Water Hammer? Four Plumbing Tips on How to Solve It

Water Hammer Can Cause a Lot of Noise and Damage

broken leaking copper water pipe
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While water hammer sounds like a complex or foreign term, it's very common and something you've probably experienced. If you have ever been in a home and heard thumping or pounding when you turned off a faucet, you have witnessed the water hammer effect. 

A water hammer occurs when water suddenly changes direction for example when you turn off the faucet. The momentum change causes pressure waves in the pipes and can be a plumbing nuisance to the point that when pressure is high, it can cause serious pipe damage.

Solving Water Hammer Problems: Install an Air Chamber

Water hammers can be solved by installing an air chamber which prevents water from generating waves that travel through the pipe. An air chamber is a vertical pipe located in the wall cavity next to the water valves where the water is turned on and off. It is recommended to install air chambers at critical locations throughout the building. An inspector cannot tell if an air chamber is working just by looking at the pipes, so in order to verify that they are working properly, you will need to do the following:

  • Shut off ​the main water valve
  • Open the building’s highest water faucet.
  • Drain all water from all pipelines by opening the lowest water faucet, normally located in the front yard or the basement of the building. Air will replace water in the pipeline, automatically filling all air chambers.
  • Once water has stopped flowing from the lowest water faucet, turn it off, and open the main valve.
  • Air pushes out of the horizontal and open vertical water lines, sputtering as it exits the faucets inside. However, air remains in the air chambers, eliminating water hammer.

The air chamber might not drain properly if it’s clogged and it should always be larger than the water supply line to reduce clogging possibilities.

Air chambers can be cleaned by removing the cap from the pipe and cleaning the debris located inside the chamber. Air chambers act as like a shock absorber, reducing the change in water pressure that causes the water hammer effect.

Pressure Reducing Valve Can Alleviate Water Hammer Issues

Water hammer can also occur when water pressure is too high. Installing water pressure regulators can solve water hammer issues due to water pressure. Whenever you have the opportunity, consider installing a pressure reducer valve at the location where the main water supply enters the home instead of installing multiple air chambers. A pressure reducing valve could also protect against high water pressure that could damage dishwashers, ​toilets, and other water-supplied appliances. A water pressure exceeding 100 psi could void warranties and damage this equipment, so a pressure reducing valve will protect against both water hammer and high pressure. Normal water pressure runs between 30 and 55 psi. To calibrate a water pressure valve, use a screwdriver to adjust it below 50 psi.

Installing Mechanical Water Arrestors

Mechanical water arrestors could be an alternative way to install air chambers in places where air chambers are impractical.

Arrestors are sealed units with a spring and air bladder to absorb the water movement, and mitigating the water hammer effect. They are the preferred alternative in commercial buildings and when used for high water pressure applications. Mechanical water arrestors do not need to be recharged like air chambers, but they will need to replaced after their life cycle has been reached. Some codes have eliminated air chambers in favor of mechanical devices.

Mechanical shock arrestors are manufactured to a nationally recognized standard from the Plumbing and Drainage Institute, known as PDI - WH201, which also includes a method of sizing these devices.

Solving Water Hammer Problems: Attaching Pipes

Water hammer could also occur when a pipe-mounting strap becomes loose. A pipe mounting strap is used to attach pipes to framing to reduce pipe movement when water is running through it.

Do not use galvanized or steel straps on a copper pipe, as material reactions could create electrolysis, leading to a plumbing leak. Clips and plumber’s tape minimizes the possibilities of water hammering in the pipeline, as they will restrict pipes from moving.