Sprinkler anti-siphon valve ok?


Old 07-10-08, 07:27 PM
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Join Date: Jul 2008
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Sprinkler anti-siphon valve ok?

I added a zone to my sprinkler system this weekend, and thought I'd clean up the previous install a bit by hiding the ugly anti-siphon valve in a container in-ground.

Well, silly me, has since read that the anti-siphon valve is supposed to be at least 6" higher than the tallest sprinkler head.


I'm wondering, given that my water supply line to the sprinkler is pretty high (see picture), and feeds the sprinkler valves below it, will that prevent the siphon?

Or do I really have to rebuild this setup?

Worse, the zone I added to the system is for drip irrigation, and so the manifolds stick up about 8" above ground -- would I really need to move the anti-siphon valve to > 14" above ground?

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Old 07-14-08, 05:16 PM
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Yes sir! in MI. the law states that the RPAVB or bac-flo preventer must be 12" above the highest head, or you can use a double check in the basement at the source.
Old 07-15-08, 01:21 PM
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Location: Spokane, WA
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Backflow Prevention

Hi ebuglet:
The plumb-out and valve set-up in your photo will not prevent backflow as bylaws intend, and it should be rebuilt in order to place the RPAVB above ground.
The reason for backflow prevention on a sprinkler system is to prevent contamination of drinking water.
In the event of a local fire, the fire department can draw water from hydrants to such an extent that a back-siphoning effect is created in the neighborhood water lines. As water is pulled back through a sprinkler system, contaminants in the yard such as fertilizers and animal feces can also be pulled into the lines used for drinking water.
In my area, a RPAVB (Reduced Pressure Atmospheric Vacuum Breaker), a.k.a. PVB, is required to be 18" above the highest head to achieve optimum backflow prevention. PVB's are usually installed on the water supply line as it exits the house. Occasionally the supply line must be routed upward into the PVB, and then routed back down into the ground where the valve manifold is situated.
A double check is another form of backflow prevention that can be installed below ground, usually at the same level and in the same location as the valve manifold.

Last edited by autorainman; 07-15-08 at 01:29 PM. Reason: To be more specific

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