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A gardener just installed a drip irrigation system in my backyard. He didn't installed the back-flow preventer. When I asked him why, he told me for drip irrigation you don't need the back-flow preventer! His argument was that in drip irrigation, we have to install a pressure reducer so there is no need for a back-flow preventer.

Is he right on his argument?

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    The pressure reducing valve has nothing to do with a back flow device. Back flow valves prevent contaminated water from entering the potable household water. A pressure reducing valve doesn't function in this manner.
    – ojait
    Sep 26 '15 at 3:37
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I think he is mistaken. A pressure reducing valve is not listed in the code among the approved backflow prevention devices:

2009 Uniform Plumbing Code 603.4.6 Protection From Lawn Sprinklers and Irrigation Systems

603.4.6.1 Potable water supplies to systems having no pumps or connections for pumping equipment, and no chemical injection or provisions for chemical injection, shall be protected from backflow by one of the following devices:

(1) Atmospheric vacuum breaker (2) Pressure vacuum breaker (3) Spill-resistant pressure vacuum breaker (4) Reduced pressure vacuum breaker

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    Thanks a lot for your reply. Is Check valve same as Backflow valve? I was trying to see a simplest option which can be installed in the line , but couldn't find one. Any hint are appreciated
    – David
    Sep 26 '15 at 3:58
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    It all depends on what code applies in your jurisdiction. In many jurisdictions including my own, the UPC applies. As you can see, a check valve is not listed as an approved device. In a residential situation an atmospheric vacuum breaker for each zone is often simplest. In a case with many irrigation zones a single pressure vacuum breaker is used, but they require protection against freezing.
    – user39367
    Sep 26 '15 at 4:18
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    Is this qualify as a backflow preventer amazon.com/gp/product/B000FPDEU8?ref_=cm_cd_al_qh_dp_i
    – David
    Sep 26 '15 at 4:36
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    Thanks Cris, I am not much worried about code, but want to do things which make sense. The Gadner have put homedepot.com/p/Rain-Bird-3-4-in-FPT-In-Line-Valve-CP075/…. From the description at home depot site it says you might not need the backflow valve. Am i right on this?
    – David
    Sep 26 '15 at 5:28
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    You should probably consult a licensed plumber in your area. The RainBird automatic valve you selected has no backflow protection. An AVB can only be installed after a valve. A PVB is appropriate for installing before a valve. Both of these devices occasionally spray water, so they must be outside.
    – user39367
    Sep 26 '15 at 6:05
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Please note that this is for your own safety. It keeps you from drinking water that's been contaminated by nasty things such as animal feces, dead critters, fertilizers, or even pesticides. It keeps you from being sued by your neighbors if they get sick. As it is a law in Texas, even rural areas, we have to abide by it. $100.00 for a PVB with fittings is cheap for the piece of mind.

See:

§344.50. Backflow Prevention Methods.

(a) Any irrigation system that is connected to a public or private potable water supply must be connected through a commission-approved backflow prevention method. The backflow prevention device must be approved by the American Society of Sanitary Engineers; or the Foundation for Cross-Connection Control and Hydraulic Research, University of Southern California; or the Uniform Plumbing Code;

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here.
    – Daniel Griscom
    Jan 14 '20 at 16:53
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Even if it isn't code were you reside it would be wise to install one for your health. But check the valves that you have installed. Many irrigation valve manufacturer's make back flow valves built into them. It's usually just above the out flow threads on the valve. Or if you shake the valve you should hear it rattle. that is the check valve that allows water to only flow in one direction.

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    If the Uniform Plumbing Code applies, then a simple back-check will not suffice. That is also not listed as an approved device.
    – user39367
    Sep 26 '15 at 4:11
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It is also important to install back-flow preventers to discourage clogging of the drippers. After the irrigation cycle finishes, the volume of the pipe that was full of water will need to be replaced by air or it will collapse at certain points. If there is no 'vacuum breaker' type valve the air will enter the line through the dripper aperture bringing with it dirt and debris. If you want to decrease clogging of drippers and occurrence of dry-spots in the garden, I'd recommend installing such a device at the highest point of each station. If the line is very long, put one every 30 metres or so.

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