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Thread: RPZ Backflow installations question

  1. #1
    DIY Junior Member ctlogistics's Avatar
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    Default RPZ Backflow installations question

    I need to install a Wilkins 975XL RPZ backflow preventer for my in-ground irrigation system. I'm getting conflicting answers from multiple city inspectors and the around the web.

    First question: Does a RPZ backflow preventer have to be installed above the tallest sprinkler head? One city inspector says yes, one says no.

    Second question: The instructions for installation say the maximum height off the ground is 30". The best place for this to come out of my house would be about 40"-50" above grade (backside of walk-out). City inspectors aren't sure about this maximum. I've seen new home installs (less than 6 months) where the units are installed more than 30" above grade.

    Any clarification would be great.
    Thanks.

  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Most codes call for a PVB backflow device on an irrigation system. That device needs to be installed 12" above the highest head on the system. An RPZ device doesn't. RPZ's are more expensive the PVB's. I would check with your inspectors to see if you can use a PVB.

    John

  3. #3
    DIY Junior Member ctlogistics's Avatar
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    Quote Originally Posted by johnjh2o1 View Post
    Most codes call for a PVB backflow device on an irrigation system. That device needs to be installed 12" above the highest head on the system. An RPZ device doesn't. RPZ's are more expensive the PVB's. I would check with your inspectors to see if you can use a PVB.

    John
    I wish the PVB would be enough. $75 vs. $250 - would be nice. However, the city was very specific about the reduced pressure device.

    The fact it doesn't have to be higher than 12" above the sprinkler head is a blessing. I appreciate the clarification.

    Now if I can just figure out the reasoning behind the 30" maximum clearance.

    Thanks for you reply. Very much appreciated.
    Last edited by ctlogistics; 09-03-2013 at 10:19 AM.

  4. #4
    Sprinkler Guy Wet_Boots's Avatar
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    There is no technical reason for a maximum height for the RPZ mounting. Considering the cost of pipe, though, economy argues well enough.

  5. #5
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    In my area RPZ must be installed 12" above the ground. The only reason for this is so you can see if the relief is dumping.

    John

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