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I am getting ready to install a Zurn 34-720A Wilkins Pressure Vacuum backflow preventer on my DIY irrigation system. The main water supply is the pipe coming out from under the storage shed. It tees off to the left for the water hose bib and the irrigation is on the right. The other two PVC pipes in the pictures go out to the yard irrigation. The second picture is a mockup of my plan.

Should I move the water hose bib to the down leg (the outlet side) of the backflow preventer as demonstrated in the third picture? That way the water hose bib will be protected by the backflow preventer and the backflow will be installed 12 inches above the hose bib.

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    In many states all outdoor hose bib’s require at least a vacuum breaker. Backflow prevention is a step up from there. Yes I would plumb the hose bib after the backflow preventer. BTW, you’re not “protecting the hose bib” you’re protecting the water supply. Also your photoshop skills are quite good, +1 for the illustrations.
    – Tyson
    Aug 20, 2018 at 11:34
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    Placing the hose bib on the irrigation side provides a convenient attachment point for an air compressor if you need to winterize things.
    – Matthew Gauthier
    Aug 21, 2018 at 3:34
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    – FreeMan
    Aug 3, 2020 at 11:52

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Do whatever the county official or water company recommends. Back flow from the spigot should not need protection so as long as the irrigation system cannot flow back to the water source you should be fine.

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    Hose bibs do require at a minimum a vacuum break this keeps water from being siphoned back into the water main back flow prevenion is always a good thing.
    – Ed Beal
    Dec 11, 2018 at 21:15

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