How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What causes a banging sound in the wall when I shut off the bathroom faucet?
Wednesday, October 17, 2018
What you experienced is called “water hammer.” When water flow is halted quickly, the water pressure has lots of energy that must be dissipated. If the water can bounce against an air cushion, pipes won’t pound. Most homes have anti-hammer devices installed in the water piping. Older homes have a foot-long elbow of pipe with air trapped at the top (as shown below in illustration “A”) located at one or several places in the system. New homes have a manufactured air chamber device called a water hammer arrestor (as shown in the illustration “B”). Over time, the older type of anti-hammer device can lose the air cushion in the pipe leg and no longer be effective.
To reintroduce the air cushion in your pipe system, do the following:
- Turn off the water to the home at the main shut-off valve, which is either at the water meter or where the water service enters the house.
- Open all faucets and allow the water to drain from them.
- Slowly open the main valve part way and close the faucets, one by one, as the water runs steadily.
- After all the faucets are running steadily, fully open the main valve.
- Test to see if the anti-hammer arresters are working by quickly shutting off a faucet.
If the above sequence doesn’t eliminate the water hammer in your pipes, we recommend calling a plumber to evaluate and repair the problem. If not fixed, repeated water hammer events will damage the pipes. To learn about water hammer arrestors, like the one shown below, that would permanently fix the problem, see our blog post What are the pipes sticking out near my water valves?
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