Pressure and GPM - Designing System

Discussion in 'Irrigation' started by jbell36, Sep 24, 2012.

  1. jbell36

    jbell36 LawnSite Bronze Member
    from KANSAS
    Messages: 1,417

    i'll try to make this short...if you have a 5/8 meter with 50 psi on one side of town and a 5/8 meter with 90 psi on the other side of town are you able to put more heads on the 90 psi even though the meter is only 'rated' for what, 12-15 GPM?
  2. cjohn2000

    cjohn2000 LawnSite Senior Member
    Messages: 570

    Pulling too much water through a meter can "knock" it out of calibration. Obviously higher friction loss through the meter and pipe to and from, which would result in a lower dynamic.
  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,764

    There are several flow-capacity standards for what you see as a 5/8 meter. The old standard was 20 gpm as maximum flow. Those meters are increasingly less common. A modern variation is a 5/8-3/4 meter, with the 30 gpm max flow rating for a 3/4 meter in the 5/8 package.
  4. muddywater

    muddywater LawnSite Bronze Member
    Messages: 1,813

    It would prob be safe to run 4 rotors per zone at 50 psi and 6 rotors at 90 psi. Using 2, 2.5, and 3 gpm nozzles depending on rotor radius. And if it hit the fan, you have room to nozzle down.
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  5. muddywater

    muddywater LawnSite Bronze Member
    Messages: 1,813

    I have flow tested a 5/8s meter to push 30 gpm with 100psi. I could run 12 rotors at once(didnt put that many on a zone but it would push all of them)
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  6. 1idejim

    1idejim LawnSite Fanatic
    Messages: 11,358

    I know you are using a good flow meter but how and where are you making your test connection?
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  7. muddywater

    muddywater LawnSite Bronze Member
    Messages: 1,813

    I tapped about 1' after the meter. Can't remember if I had the backflow on at that time or if it was before I put the backflow in. I posted a thread about a year ago, and Kirl said I should have had about 20' of pipe after the flow meter to get a more accurate number, but I think it was close. It would push 12 5004 rotors with average 2.5 gpm nozzles.

    This was the first house in the neighborhood, so it was probably a lonely water main.
  8. muddywater

    muddywater LawnSite Bronze Member
    Messages: 1,813

    Well dug up those pics. Looks like it read 49gpm which sounds a little high. I know it probably had 60 psi dynamic pressure(visual guesstimate) with 12 heads running.


  9. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,174

    Love those fuzzy, upside down/ sideways pics. :dizzy:
  10. txirrigation

    txirrigation LawnSite Senior Member
    from Texas
    Messages: 977

    Or you can use the three variable equation. haha I kid I kid.

    I have in fact passed this super secret equation on to another member though. They now hold the holy grail.

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