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Stop! Hammer Time

No not the guy, the hammering you hear in the wall when the water is shut off. Water hammer.

Imagine—you just finished filling up a pitcher of water at the kitchen sink and everything seems normal, but the moment you turn the faucet off, the pipes start rattling so loudly you think the entire house might just collapse.

Water hammer is loud and obnoxious, and although many homeowners have experienced it at one time or another, there are still many misconceptions about it.

Below we discuss the causes of water hammer, solutions for dealing with it, and how you can prevent it from happening in the future.

Why It Happens

Water hammer isn’t just a generic term for loud pipes. Water hammer is a specific plumbing term, and it happens when a large amount of water is stopped quickly, causing a shock wave to run through the piping system. The rattling you hear is the result of a lot of water slamming into a closed valve.

Air chambers, which are vertical pipes located where the water-supply pipe exits the wall, are installed to help prevent water hammer. When a valve closes, the air from these chambers compresses and prevents the water from hitting the valve too hard. If these chambers are blocked, damaged, or waterlogged, there is no cushion to prevent the impact.

In addition to waterlogged air chambers, water hammer can also result from having loose mounting straps. When these metal straps don’t fit snuggly, the pipe can vibrate against them when water is turned on and off.

Excessively high water pressure can also be a culprit. The quicker the water is moving through the pipes, the more of an impact it will make when a valve suddenly closes.


When your pipes start to rattle, chances are, you need to replenish your air chambers with air. Head down to your basement and shut of your home’s main water supply valve.

Open the highest faucet inside your house. Then find the lowest faucet, which is usually on the first floor outside or in the basement, and turn it on. The water left in the pipes will start to drain, and as it does, air will replace it.

When the water is completely drained, turn off the lowest faucet and reopen the main value. Water will be pushed out the main water lines but will remain in the air chambers.


Preventing water hammer takes occasional maintenance like any other plumbing problem.

Check all accessible pipes once or twice a year to make sure their mounting straps are tightened and properly connected. Doing so will prevent unnecessary vibrations.

Most modern homes have a water pressure regulator, but if yours doesn’t, consider installing one. Paying your local plumber a few hundreds bucks up front will be a good investment in the long run. Not only does high water pressure increase the likelihood of water hammer, it is also wasteful and can damage washing machines and other water-supplied appliances.

Test your water pressure whether you have a regulator or not. You can either do it yourself with a water-pressure gauge or call a professional.

Normal water runs between 30 and 55 psi. Just to be safe, it’s best keep the pressure below 50 psi.

Final Thoughts

Now the next time your pipes start to rattle, you’ll know why it’s happening. Use the tips and information in this article to take care of the problem sooner rather than later, and share it with your friends if they’re having water hammer issues too.

How have you dealt with water hammer in the past? Any tips?

Share them in the comments!

Image: Flickr