3/4" Backflow or 1" Backflow? GPM

Discussion in 'Irrigation' started by jbell36, Sep 25, 2013.

  1. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,490

    The actual maximum flow ratings for backflow preventers matches that of water meters of the same size, and that is way off the charts compared with what flow rates you will actually be working with. You can get away with high flow rates in PVBs and DCVAs much more than you can with RPZs, which will spit water from the relief valve when a downstream valve slams shut.
     
  2. jbailey52

    jbailey52 LawnSite Bronze Member
    Posts: 1,061

    So can someone explain a little more to me... If you use a 3/4 backflow on a 5/8" meter, what size pipe is feeding the backflow, and which leaves the backflow? All 1" with 3/4" fittings for the backflow?
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  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,490

    Not enough information. Variables include length and diameter of the supply line going into the meter, and from the meter to your point of connection.
     
  4. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,616

    I don't get it, the price of a 1" vs 3/4" asembly is minor, it should be run from the setter in brass and a sch 80 mip to tie into the downstream main. Anyone who runs 3/4" mainline joins the hall of pikers and hacks. I wrote the regs for my purveyor and specified unions on both ends.
     
  5. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 46,490

    The price of brass being what it is, I could see a 3/4-inch full-port system shutoff valve and 3/4-inch DCVA with a 12 gpm flow. Of course, it used to be that most 3/4-inch DCVAs were using the same body casting as the 1-inch ones.
     
  6. txirrigation

    txirrigation LawnSite Senior Member
    from Texas
    Posts: 977

    We install 3/4 and run a 1" main. We limit all systems to 12gpm. It's had worked great the last 3,000 times we've done it...
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  7. AI Inc

    AI Inc LawnSite Fanatic
    Posts: 25,164

    We don't use dcva's. Cant , illegal here. Difference between 3/4 and 1" pvb is so small its not worth stocking more parts. Not to mention my fingers don't fit inside a 3/4 to rebuild.
     
  8. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    Can't do dcvas here either.
    3/4" PVbs are the most used here, then 1" PVB, then 3/4" RP. Rarely see a 1" RP.
     
  9. AI Inc

    AI Inc LawnSite Fanatic
    Posts: 25,164

    Although I will admit when a rp fails and it will, we replace em with dcva's
     
  10. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,616

    Obviously, you have no adult supervison, that is crossing the line. :rolleyes:
     

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