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January 14, 2015
Have you noticed a banging noise coming from your walls when you flush a toilet or run your washing machine?
This is known as “water hammer” and can be quite a nuisance.
Let’s look at why this happens and how you can fix it.
Why water hammer happens
To understand what causes water hammer, think about a train.
It’s chugging along at full speed and, all of a sudden, a large boulder rolls onto the track. The train crashes into the boulder, causing every train car to crash into the car in front of it—making a lot of commotion.
This is similar to what happens, on a smaller scale, inside your pipes.
When you flush your toilet, water runs through the pipes quickly. But as the toilet finishes filling up, it suddenly closes a valve, causing water the crash against it.
This creates noise and vibration, sometimes causing the pipe to bang against the wall (aka the water hammer).
How to eliminate water hammer
The fix to your water hammer problem depends on when and how your home was built.
If your home was built in or before the 1960s:
Older homes were frequently built with air chambers to prevent water hammer. An air chamber is simply a pipe connected to your pipes with a “T” fitting and capped off at the top. This capped off pipe was filled with air.
From our train analogy, an air chamber is like a switch in the train’s track that allows the train to use an alternate track to avoid the boulder and safety come to a complete stop. The air space compresses and absorbs the shock.
However, these air chambers can eventually become completely filled with water (making them ineffective), leading to water hammer. Because of this, air chambers have been pretty much discontinued.
Luckily, there’s a simple fix. Here what you need to do:
Turn off the water supply to your home.
Drain all the water from your home’s pipes — open all the faucets, flush all the toilets and run the washing machine and dishwasher.
Turn the water back on.
If your home was built between the 1970s and 1990s:
Homes built from the 70s through the 90s typically have little to no water hammer protection. So if you are noticing loud, knocking noises from your pipes, you will likely need to contact a professional plumber to have water hammer arrestors installed.
See below for more info on water hammer arrestors.
If your home was built since the 1990s:
Modern homes are built with water hammer arrestors.
These are small devices that are connected to your water pipes and contain a spring-loaded shock absorber. This spring absorber diverts the force of the water when a faucet is shut off, greatly reducing water hammer.
And unlike the air chambers of old, these devices never become water logged.
So if your home is newer, and you’re experiencing water hammer, one or more of your water hammer arrestors may have malfunctioned (although this is rare), or there were no water hammer arrestors ever installed.
Other problems that can cause loud, banging pipes
Sometimes the banging noise isn’t water hammer. If you have functioning air chambers or water hammer arrestors, you might have a different problem:
The straps that connect your plumbing to your home’s wall studs could be loose, causing the pipes to vibrate. (This can actually be caused by water hammer.)
High water pressure. Your home may need a pressure reducer valve installed to quiet the pipes.