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Thread: Pressure drops to zero when pump comes on

  1. #1

    Default Pressure drops to zero when pump comes on

    I installed a new jet pump, pressure tank, and check valve on my sand point well this spring in my cabin and everything was working great until about 1 month ago. When we first arrive at the cabin and start using the water the pump will cycle and as it turns on the pressure drops slightly. Normal enough. As the pump cycles on throughout the weekend the pressure drops to zero and there is no water coming out of the faucet for about a minute until I assume the pump gets re-primmed, then there is water again. I thought the check valve had a leak on the well side, and the water was falling back down the well so the pump had to get re-primmed every time it came on. I've tightened the valve but it is still happening. Could I just have a bad check valve and need to install a new one. I have not taken note of the exact PSI that the pump is kicking in at (I assume around 30-35psi, whatever it is set to at the factory) so shouldn't I have a little pressure left after the pump comes on? Instead it drops right to zero until is sucks water again. Someone said the pressure switch could be clogged but does that make sense? Why would the pressure drop to zero?

  2. #2
    Master Plumber nhmaster's Avatar
    Join Date
    Jul 2008
    S. Maine


    The pressure would drop to zero because the pressure switch isn't calling the pump to run so you use up the water (and pressure) in the tank. Eventually the pressure switch feels the drop and calls the pump again. If the check valve was bad or you had a suction leak you would have to prime the pump everytime. Shallow well pumps are not self priming.

  3. #3


    Actually the pump starts up first and then the pressure drops to zero at the faucet and no water comes out until the pump starts to suck water again. It takes about a minute until the water flows after the pump comes on.

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default flow

    That usually means your tank's precharge is higher than the pump cut in/turn on point so the tank runs out of water but the pump stays off until the pressure on the water in the piping drops to the cut in point.

  5. #5
    Moderator valveman's Avatar
    Join Date
    Mar 2006
    Lubbock, Texas


    Sounds like you have a check valve between the pump and tank. I would remove this check valve so the pump has the same as tank pressure when it starts.


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