Pipes Knocking

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greggor36

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Hello - Every time I run my washing machine or dish washer, the pipes bang when the water is shut off during their cycles. I've also noticed the toilets in the house also give a light bang when shutting off. I've had a water arrestor installed on the washing machine line but that hasn't helped. I have also had the whole townhouse water pressure adjusted to a safe, required level as well but the knocking continues. My questions are...

1. Is there anything I can do to stop the knocking of pipes? Would the walls need cut into in order to inspect and fix the knocking?

2. What's the liklihood one or more of the pipes could burst within the walls if this isn't repaired?

Thank you for all advice and help!
 

Reach4

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I've had a water arrestor installed on the washing machine line but that hasn't helped.
You need one for hot and one for cold.

Maybe you need bigger water hammer arrestors.

If this is an older house, you might get some improvement by turning off the water and drain water from your lower outlets. This is because older houses had water hammer arrestors that were just empty vertical pipes that may drain water after a while with the water off and faucets open. They may not drain out. Seems worth a try.
Air-chamber-200.jpg
 

Widgit Maker

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Air chambers (if installed) are water logged. Air chambers are vertical sections of pipe installed at each fast acting valve (toilets and single handle faucets). Air gets trapped in these air chambers and acts as a cushion when the flow of water is abruptly stopped. Over time the air is absorbed by the water and must be recharged. Air chambers are the same thing as water hammer arresters except they have no bladder.Turn off the water to the home. Open all faucets and flush all toilets. Let the pipes drain. Wait as long as possible before turning the water back on. The water in the air chambers can be held a vacuum and it may take some time for the air chamber to loose its vacuum.
Close all faucets and close the stop valves at each toilet. Turn the water back on. Let the air trapped in the line push it way up into the air chambers.
Single lever faucets let water out because it is under pressure. They don't let air in very well. It may be necessary to disconnect the supply tubes or remove the valve stems of stop valves to let air in.

This process has to be periodically repeated.

It may be helpful to install a expansion tank on the main cold water input line. It is basically the same thing as a giant size water hammer arrester.
 

greggor36

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Thank you Reach4 and Widget Maker! You both gave me some good ideas and things to try! I’ll let you know how things turn out! Thank you both again! You guys are the best!
 

Jadnashua

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FWIW, air chambers are mostly a waste of time and materials. IF you need arrestors, an engineered one needs to be installed. It helps to install them as close to the offending valve as possible. I have mine for the WM attached to the WM, not at the valves before the hoses.

You mentioned water pressure, but what is your current water pressure? Code wants it to be no greater than 80psi, and many find that is more than they need. That bang is caused by the inertia of the water movement. The more pressure, the faster it moves, the more energy it has and the harder it is to stop it quickly, just like trying to stop your car. Some toilet fill valves have a more gradual shutoff than others, and changing the toilet fill valve may help. If you can stand the extra time it takes for the WM to fill, you could try partially closing the valves which limits the volume (not the pressure), and volume equates to weight and energy, making it easier for the arrestor to do its job.
 

greggor36

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FWIW, air chambers are mostly a waste of time and materials. IF you need arrestors, an engineered one needs to be installed. It helps to install them as close to the offending valve as possible. I have mine for the WM attached to the WM, not at the valves before the hoses.

You mentioned water pressure, but what is your current water pressure? Code wants it to be no greater than 80psi, and many find that is more than they need. That bang is caused by the inertia of the water movement. The more pressure, the faster it moves, the more energy it has and the harder it is to stop it quickly, just like trying to stop your car. Some toilet fill valves have a more gradual shutoff than others, and changing the toilet fill valve may help. If you can stand the extra time it takes for the WM to fill, you could try partially closing the valves which limits the volume (not the pressure), and volume equates to weight and energy, making it easier for the arrestor to do its job.
 

greggor36

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Thanks for your input jasnashua! I appreciate it! I will check the psi on my water pressure. I thought it was set to an acceptable level when they fixed the main valve but I'll double check. Thank you again! Your input is very valuable! I'll see what I can do from all the suggestions to get this fixed. Thanks again!
 
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