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Thread: Second set of valves is causing watering hammer?

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    DIY Junior Member breakpoint's Avatar
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    Default Second set of valves is causing watering hammer?

    Hello all, I have two set of irrigation valves, one set for the front yard and the second set for the back yard. While the second set turning off one after another after watering, a loud bang could be heard under the house where the water supply runs on copper. But I have no trouble at all with the front yard valves where located in the front yard and the second set located in the back yard. The only difference I can see from observing them is that the back yard valves are not raised high enough (6") wihen compared to the front yard valves. Can this be the problem? The irrigation system is layout with PVC pipes (1") and just had them for months. Please advise.

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    Forum Admin, Expert Plumber Terry's Avatar
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    It depends on how fast your valve is shutting off. A quck closing valve will create water hammer. Solving water hammer with a hammer arrestor is your best solution.
    You can buy them in different sizes.

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    In the Trades Jerome2877's Avatar
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    Distance adds to water hammer as well, the farther the run the more water hammer. A hammer arrestor just upstream of the shutoff will stop this.

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    DIY Junior Member mr-C's Avatar
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    Quote Originally Posted by breakpoint View Post
    Hello all, I have two set of irrigation valves, one set for the front yard and the second set for the back yard. While the second set turning off one after another after watering, a loud bang could be heard under the house where the water supply runs on copper. But I have no trouble at all with the front yard valves where located in the front yard and the second set located in the back yard. The only difference I can see from observing them is that the back yard valves are not raised high enough (6") wihen compared to the front yard valves. Can this be the problem? The irrigation system is layout with PVC pipes (1") and just had them for months. Please advise.
    I just went through this after working on my sprinkler system. I'm an engineer and here's my conclusions:
    The so called water bleed screw is really an air bleed screw. When the valve is installed the air bleed screw should be the highest part of the valve. It bleeds the air trapped on the back side of the diaphragm after replacing a valve or repairing. If there is air there, the valve will bang several times when opening or just before closing. This happens because air is compressible while water is not. You must have 100% water behind the diaphragm or else the valve will misbehave. The bleeder screw may be used for other things but its primary purpose is a means to get rid of the air. If the valve is not installed with the screw being high one may not ever get rid of the air.

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