Pump sizing

Discussion in 'Irrigation / Sprinkler Forum' started by dougle, Mar 16, 2008.

  1. dougle

    dougle New Member

    Messages:
    21
    What would happen if i connected a jet shallow pump 3/4hp to a system (lateral)that required only 5 gpm. Flow out of the pump with no pressure (no resistance) is 9gpm. I have no pressure settings on this pump, turn it on and let it pump. Will the pump burn out as the resistance (5gpm) is not enough for the pump? i know that the pressure will increase as it tries to put 9 gpm out. have i got this right? just trying to size a system.
  2. Bob NH

    Bob NH In the Trades

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    3,317
    Location:
    New Hampshire
    The pressure will increase and the pump should work fine.

    Shallow well jet pumps are tolerant of throttling and will operate at a point that is stable for the conditions of lift and discharge pressure. The final pressure will depend on suction lift and flow rate and will probably be somewhere in the range of 50 to 70 psi.
  3. dougle

    dougle New Member

    Messages:
    21
    Thanks Bob, I assume then that increasing the flow rate (ie adding another head) would reduce the pressure? (ie to 40-45psi) thanks
  4. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Yes. You can test the pump, or look at the curve for the particular model.

    9 GPM is quite low flow for a 3/4 HP shallow well jet pump.

    Here is data for a Goulds 3/4 HP J7 convertible or J7S shallow well jet pump. The unbolded entries are GPM at the Pressure/Lift conditions.

    . . . . Pressure - PSI
    Lift, 30.0, 40.0, 50.0, 60.0, MaxP
    5 ft, 21.3, 18.3, 12.5, 6.6, Max70
    10 ft, 18.8, 17.3, 11.3, 5.0, Max 68
    15 ft, 16.4, 15.5, 9.6, 3.7, Max 66
    20 ft, 13.6, 13.2, 8.3, 2.0, Max 63
    25 ft, 10.0, 9.9, 6.4, 1.0*, Max59

    *The 1.0 GPM entry at 60 psi doesn't make sense for a pumping condition that makes 59 psi max but that is what was in the table.
  5. dougle

    dougle New Member

    Messages:
    21
    Thanks so much Bob.
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