Knocking-Jack Hammer sound from pipe

Old 07-14-01, 12:05 AM
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I have a problem with a knocking pipe. It is only one pipe and it is only when I turn on the outside sprinklers. Is there anything that can be added to the pipe that supplies the sprinklers to quiet it down.
Old 07-14-01, 03:44 AM
Mike Swearingen's Avatar
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The pipe is probably knocking where it passes through or against wood due to normal water pressure running through it.
Locate those points, and tap a wood wedge into the hole with the pipe, or clamp the pipe to the joist or whatever.
Good Luck!
Old 07-14-01, 06:28 AM
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Here is another thing to consider.
Water pipe can only carry so many Gallons Per minute. Each size a max. If you have pressure on the high side lets say for example over 60 lbs and you have a small pipe that is getting the max GPM pushed through that pipe.
The water is going through the pipe very fast. This increases the chance for what is known as water hammer. The two cheif causes are amall pipes and high pressure.

The two main fixes are increases water pipe size which will decrease the velocity. Or decrease the pressure. With a sprinkler system the performance could be affected by decreasing the pressure. Increasing the pipe size would improve performance.

If this is what is causing your issue poor design of the sprinkler system is the number one cause of water hammer. There is an excellent web site on the subject at:
It has all the information you will ever need on sprinkler systems. I used the information to design mine and it works great and I have fewer stations than many in the neighborhood.

Good Luck
Old 07-15-01, 04:30 PM
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Thanks you guys for your quick responce to my knocking problem. When John mentioned a pipe/pressure issue possibly causing the problem, I turned the pressure down at the pipe that supplies the sprinklers, knocking was reduced dramatically and I was still able to get good coverage.

Thanks Guys.

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