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Old 02-16-2011, 09:25 PM  
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Location: Yorkville, IL
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Default 'Water Hammer'?

I have been living in my home for a year now and every time I shut off a faucet, washing machine cycles, etc. the pipes knock.

The home is a ranch built in 1992. I have tried to drain the system to recharge the air chambers numerous times to no avail. I have installed Oatey knock arrestors in both the hot and cold water lines under the 2 bathrooms on the west end of the house and under the laundry/kitchen sink on the east end of the house... The knock is still there.

I have gone through every pipe hanger that I can find to make sure the pipes are not loose and re attached where they were.

I bought a water pressure gauge and tested the water pressure on the house and it is around 52 psi at rest when tested on the west side of the house near the water meter. When the washer cycles (washer is on the far east side of the house) the pressure never spikes over 60 psi.

I'm lost here...the knock arrestors say they pretty much all come with a 60 psi charge in them. Does this mean that they will do nothing until the pressure spikes over 60psi?

Any help would be greatly appreciated.

Thanks for reading!

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Old 02-17-2011, 02:14 PM  
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Yes that is what happens. Water hammer is a momentum thing where the momentum of water traveling in the pipes is suddenly stopped, and for a moment there is a sudden pressure increase at the point where the water is stopped that could actually go quite high, but you would see it as the needle of the gauge bouncing because it can't react quick enough to record the full pressure increase. The hammer arrestors absorb this.

I will say that somewhere possibly in a location you can't access there are improperly secured pipes. Possibly undersized pipes as well because they would increase the flow velocity.
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