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What is Water Hammer

By May 12, 2021May 26th, 2021No Comments
water hammer

Have you ever heard a loud banging or knocking sound in your pipes right after the flow system of water shuts off? This was probably what is known as water hammer. What is water hammer? It happens when fluids are forced to change direction or stop abruptly in a water system. The water slams into it and a shockwave occurs. The banging noise is the result. This is not a good thing and we will look at how to prevent it.

We will discuss why you need to know about water hammer, the causes, effects, how to prevent it, other things to think about, and when to call a professional.

Why You Need to Know About Water Hammer

When water hammer happens, you might think it is no big deal. However, the water slamming into the system can cause pressure spikes, hydraulic shock, and long-term effects to the system. Also, it can happen in any pipes in or outside of the home. We will look at the effects and how to prevent them from happening so you aren’t spending thousands of dollars for a repair or replacement.

Causes of Water Hammer

Water hammer can be caused by four different situations:

1. High Water Pressure

This can come from a faucet, appliance, or average use in the household. Do you hear water hammers frequently? It could be that the water pressure is too high. Thus, requiring you to buy a residential water pressure gauge kit.

  1. To test it, turn off all the appliances that use water. This includes the refrigerator and irrigation system.

2. Then, screw the pressure gauge onto a valve or hose bib that’s close to your main water supply source

3. Open the valve slowly until it’s fully open.

4. Next, when the needle on the gauge stops moving, read your residential pressure.

5. Lastly, test one more time to be sure the reading is accurate. If the pressure exceeds 80 psi, you will need to contact a professional to install a pressure regulator or replace an existing one on the water main.

Make sure to turn the appliances back on and notice if there are any issues. Did you find that the sprinkler system won’t turn back on? You will need to investigate as well as any other appliances that don’t turn back on.

2. Old Pipes

Old pipes don’t fit securely together anymore after several years and can wiggle when water flows through or a water hammer occurs. Going into the basement or crawl space to check the pipes is a good idea. Try wiggling them some to see if they move. If they do, you will need to get pipe supports or plumbers tape to hold them together better. Remember if you have copper pipes, don’t use galvanized or steel straps. Mixing the metals can cause issues.

You may want to contact a professional to see if it is time to replace your pipes and the material that would be good for your home.

3. Water in Air Chambers

These are vertical pipes that keep the waves from forming in the pipes and regulate the water pressure. It is important to have these as they can help prevent water hammer. Older pipes may not have them so calling a plumber to install them is a good idea.

Sometimes water is stuck in the air chambers and by opening up all of the faucets, you can get the water cleared out. To do this:

  1. Turn off the main water supply
  2. Open faucets and valves, and allow the air chambers to drain
  3. Turn the faucets off and turn the water back on and this should fix the problem
Water hammer arrestor

4. A Strong Appliance That Causes It

The cause may be one of your appliances such as the washing machine, the dishwasher. sprinkler system, or another appliance. If you hear the water hammer when the appliance turns on or off that might be the culprit. Installing a water hammer arrestor may fix the problem. There are various types so you may need to contact a professional to help you get the right one installed.

The Effects of Water Hammer

1. Damage to the Pump and Flow System

Ignoring when water hammer happens can be catastrophic. This is because even if the water hammer only happens one time, there can be damage to gasketed and expansion joints, damage to pumps, valves, and instruments. In addition, collapsing of pipe walls and welded joints can happen.

water hammer

2. Leaks

Leaks can occur because of damage that is done by the water hammer. They may start as small leaks but the damage done might not be noticed for a while.

3. Property Damage When Pipes Rupture and Fail

The rupturing and failing of the pipes can shut down the whole system and cause a lot of money for replacement. In addition to the replacement, the water can also cause damage to electrical systems. This depends on where the failing pipes are.

water pressure reducing valve

How to Prevent Water Hammer

There are several ways to prevent water hammer:

  • Air chambers- as mentioned above, these can help in reducing the amount of force of the water when the valves close.
  • Flush old systems to clear them out
  • Install pressure reducers and regulators in the supply line
  • Reduce operating pressure
  • Reduce pressure in the lines with silent check valves or ones with springs

Other Things to Think About

When you are checking the pipes and appliances, there are a few other things you can do as well.

In the winter, make sure you put outdoor faucet covers on the spigots. This will help keep the pipes from freezing. Also, if you go out of town for a while, or maybe you are a snowbird down south, you will want to winterize your home. Adding the faucet covers on so it will help keep people from using your water, along with keeping pipes from freezing is a good idea. Don’t forget to dewinterize your home when you return.

Check valves in the home – one of those is on the water heater. You may need to flush the water, so you can do this when you are also checking the air chambers. Your water heater is usually located in the garage and has a TPR valve or sometimes called a T&P valve.

When to Call a Professional

Call a professional if you aren’t sure why water hammer is happening or you discover other issues. You will also want to find out if you need to replace pipes or an appliance how much it will cost. The idea is to stop water hammer from happening before the damage is done.


If you notice water hammer happening in your home, a little investigating can help prevent it from reoccurring. Catching it early is important to avoid damage. We can listen for the sounds of water hammer in your home while conducting a home inspection in the Atlanta area. Think you may need our services? Leave us a comment below!

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