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Thread: pump sizing advice

  1. #1
    General Engineering Contractor ballvalve's Avatar
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    Default pump sizing advice

    Got a 350' deep well. Hit water at 305',came up to 25' from top. Driller says 30gpm. So theoretically no drop in pumping height if I am moving 10 gpm.

    Have a old stock Dayton pump, older, heavy, maybe a Myer with cast iron head. Its a 10 stage head, I put a franklin 3/4HP motor on it. Going to fill a 5000 tank with tethered float valve - no outlet psi. If the water stays at 25'. its another 50' up to the tank. So perhaps 75' head with no outlet psi.

    What do you think. No need for fast refill. I think I might need to throttle it back to up the head [?] -keep the amps in range. Any thoughts?

  2. #2
    Moderator valveman's Avatar
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    A 10 GPM, HP should pump 5 or 6 GPM at 300 feet. It only needs about 100’ or 40 PSI on it to keep from being in upthrust. So if you are running a 40/60 pressure switch, or into an irrigations system that is zoned for less than about 12 GPM, you already have enough backpressure.

    If you are filling a cistern, you should use a ballvalve, (of all things ) to keep about 40 PSI back on the pump.

  3. #3
    General Engineering Contractor ballvalve's Avatar
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    Thanks, thats about what I thought for the cistern. I suppose checking amp draw, keeping it under FLA along with psi would be ideal.....

  4. #4
    Moderator valveman's Avatar
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    Most submersible pumps are non-overloading. They won’t pull higher than FLA, even when pumping out of a barrel with no discharge pressure. So it is hard to set a throttling valve according to amperage. If you throttle enough to see the amperage drop a bit, it maybe throttled more than it has to be. Won’t hurt anything, but you maybe leaving a few GPM in the well.

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