Uh-oh, potential backflow hazard?


Old 04-26-09, 02:21 PM
Thread Starter
Join Date: Oct 2006
Location: SF, CA
Posts: 66
Uh-oh, potential backflow hazard?

Yikes! I may have made a huge mistake in plumbing my drip irrigation system.

I have a rainwater catchment tank with a pump that connects to a manifold with 5 anti-siphon irrigation valves. Four of the valves go to watering zones one of the valves comes from the house water supply. I mounted the valve coming from the house such that the anti-siphon portion of the valve should prevent water from the tank back-flowing to the house. However, now that I think about it the anti-siphon irrigation valves may not be designed for significant water pressure, the pressure from the pump is around 50 psi.

Anyone know if this is the case? Is the anti-siphon valve designed only to prevent the siphon from a drip zone?

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Old 04-26-09, 04:47 PM
Join Date: Nov 2008
Location: Michigan
Posts: 386
the anti-siphon valve, or atmospheric valve is not legal in many places anymore. You are correct that the 50 PSI coming out of the pump could potentially push water backwards into your house. I would hope it wouldnt do any harm, but its possible. Reversing the flow forcibly into your house is never a good thing either... depending on the PSI of your home supply.

Using the rainwater collection for the drip is a great idea so long as you filter out any debris from the gutters.... this can cause the drip tubes to clog.

It might be easier to seperate the single zone that runs from the house water from this water collection system but I think you are using the house water as a backup in case you use up all of the water in your tank.

If that is the case you will most likely need a backflow prevention device (also called a vacuum breaker). Your city or township or whoever is in charge of this in your area would have some guidelines of what you need to make this legal. You could be one of the few places where an atmospheric valve is still legal, but they are quickly becoming a thing of the past. Fast.

There are some other things you could do but I do not wish to reccomend anything that could potentially be illegal where you live. Having a fine and your water shut off is not very fun.
Old 05-01-09, 10:35 AM
Thread Starter
Join Date: Oct 2006
Location: SF, CA
Posts: 66
I spoke with the local sprinkler supply store and they told me that by code I should probably have a double check backflow prevention valve but that a check valve rated to 30psi would probably work. There is a backflow prevention valve installed at the meter, so my main concern is water backflowing to the house.

I purchased the check valve and a 30psi pressure reducer.

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