Shut-off psi

Discussion in 'Pumps and Tanks Well Forum & Blog' started by Bob999, Aug 13, 2009.

  1. Bob999

    Bob999 In the Trades

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    448
    Location:
    Pennsylvania
    One of the rating factors for submersible pumps is "shut-off psi". Where is this pressure measured--at the pump or at the pressure tank?

    If it is measured at the pump then what is the formula for determining the maximum pressure that could be developed at the pressure tank?
  2. valveman

    valveman Moderator Staff Member

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    Location:
    Lubbock, Texas
    Shut off head minus static water level gives max pressure available at the surface.
  3. Bob999

    Bob999 In the Trades

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    448
    Location:
    Pennsylvania
    I want to make sure I understand your answer and that it applies to the data I have.

    My pump as a Grundfos 16S15-14 with a 1.5 hp motor. The published data is posted here:
    http://www.us.grundfos.com/web/download.nsf/Pages/9CA58FA9920C5CFB88256561006FDC9C/$File/S4_16-ez.pdf

    Note that the "shut-off psi" varies with lift.

    In my example the well is 200', the pump is at 175' and the static water level in the well is 90'.

    So I am trying to determine the maximum water pressure the pump will produce at a CSV located at the surface.

    Am I correct in using the following: interpolating from the Grundfos table linked above the shut-off psi is 145. If I subtract the static water level of 90 ft then the max pressure at the CSV is 145-90=55 psi? This doesn't seem to yield the correct answer because my pressure switch is 40/60 and the pump does provide 60 psi to the tank.
  4. valveman

    valveman Moderator Staff Member

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    Location:
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    A 16S15-14 has a shut off head of 405' or 175 PSI. Take the 90' the pump has to lift away from the shut off head and you get 315'. Divide 315' by 2.31 to get 136 PSI shut off head at the surface. So max pressure on the inlet of the CSV is 136 PSI.
  5. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
    Cave Creek, Arizona
    well

    The specifications tell you that if the dynamic water level is 400' below the surface, the the pump will deliver 200 gph, and will only be able to deliver 25 psi of pressure to the system at that depth. If the pressure switch were set above 25 psi, the pump would never shut off, and would probably overheat or destroy itself because of cavitation.
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,579
    Location:
    Lubbock, Texas
    If the shut off head of the pump is 405', then if the water level is 405', the pump is moving 0 flow. If the water level is 400', then the pump will only be able to lift 5'more, or deliver 2.1 PSI more pressure but, that is at 0 flow rate. Since the pump is set at 175', if the water level pulls all the way down to 160', that pump will still deliver 15 GPM at 60 PSI.
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