How deep can a pump "suck" water from?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by gsecord, Jun 16, 2008.

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  1. gsecord

    gsecord New Member

    Messages:
    14
    Location:
    michigan
    can somebody explain why a shallow well pump wont suck water at a depth of 29 ft? what kind of pump will and do you have any suggestions
    thanks
    george
  2. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    A shallow well pump won't suck water from 29 ft because it is at or beyond the limit of the physics and mechanics of the system.

    "Sucking" water doesn't actually describe how it works. A shallow well pump removes air from the suction line and allows atmospheric pressure to push the water up. Because atmospheric pressure is limited (about 14.7 psi at sea level, but only about 14.2 psi in Michigan) that is the limit to which it can push the water. A pump can't produce a perfect vacuum because the water evaporates at perfect vacuum, but the real limit is a characteristic of the pump that requires a minimum Net Positive Suction Head, often abbreviated NPSH Required. It requires that minimum pressure (NPSH) to avoid cavitation at the inlet of the pump.

    Because of those factors, the limit for reliable operation of a shallow well pump is usually given as 25 ft of lift from top of water in the well to the inlet elevation of the pump. That is further diminished if the line from well to pump is too small or too long so that it causes additional pressure loss in the pipe.

    The alternative is to use a deep well jet pump that involves putting a venturi/ejector in the bottom of the well with a supply pipe and a lift pipe; or make the well big enough to install a submersible pump, which is usually a 4" minimum diameter well. Deep well jet pumps are so inefficient that most new deep wells are drilled large enough for a submersible pump.
    Last edited: Jun 17, 2008
  3. gsecord

    gsecord New Member

    Messages:
    14
    Location:
    michigan
    shallow well

    ok bob thanks for the information it was very helpful talk at you later
    george
  4. hj

    hj Moderator & Master Plumber Staff Member

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    suck

    A contractor came into our store once. He was building a concrete "slip form" building in Texas and wanted a pump to suck water to keep it lubricated as it was moved upwards. He wanted the tank to be on the ground and the pump to be on the successive floors as they were finished. I told him, "You can pump the water all the way to the Moon, but you can only "suck" it 25 feet". 15 psi air pressure at the Earth's surface it the limiting factor. The higher your elevation, the shallower the well has to be.
  5. pudge565

    pudge565 New Member

    Messages:
    24
    For every foot that you pull the water you will lose .5 psi. so at normal atmospheric pressure you should be able to raise the water about 28-29 feet. just learned this through a pump class for firefighting.
  6. Redwood

    Redwood Master Plumber

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    7,450
    Location:
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    Then there is the perfect vacuum factor...
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,301
    Location:
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    vacuum

    Which is the operational factor for a water filled barometer, at least until the water freezes.
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