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Thread: Pump Loses Prime When Off

  1. #1
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    Pump Loses Prime When Off

    Replaced a 10yr 1.5 HP Jaccuzi Magnum force pump (pump had a flapper acting as check valve inside basket) with a 2 speed 1.5 HP Pentair Whisperflo.

    All works except pump slowly loses prime when shut off. Pump basket half full after 3 hours of pump being off.

    -Detected one leak before pump when pump shutoff and water squirted out. Added additional PVC glue. No more water detected when pump shuts off.
    -Added PVC tape and solvent to all PVC male thread and PVC unions.
    -Used red food color at all connections before pump and no detection.
    -With pump off and inbound valves shut I get slow bubbles coming pump intake up to the glass cover. I would have thought I would see leaks since all connections are below pump basket.
    -The chlorination system and other system between heater and filter not used for several years.
    -Spa drain (closed valve) typically closed during normal pump operation.

    -I might have had this problem all along and the previous pump with flapper minimizes the issue.

    Any idea on what to check next.
    Attached Images Attached Images
    Kenbob
    inground, 23,000 gallons, vinyl liner, sand filter, 2 speed Whisperflo 1.5 HP, gas heater

  2. #2
    Mod Squad Bama Rambler's Avatar
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    Re: Pump Loses Prime When Off

    Common places for an air leak is pump strainer basket lid, the drain plugs, those valve handles and unions. Low water in the skimmer is also common.

    It was most likely there all along but the check in the other pump masked it.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 1.5hp Dynamo pump. 24" Pentair Sand Dollar Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit
    You can stop SLAMing your pool when you pass the OCLT (You lose 1ppm or less FC overnight, & You have .5ppm CC's or less) & your water is clear.

  3. #3
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    Re: Pump Loses Prime When Off

    Update: wrap a bag around the coupler between the 2 90s before pump and filled it with water and the small amount of bubbles when pump was running went almost clear suspect that is where the leak and causes the slow drain of pump basket when pump is off. Still not sure why it does not leak when pump is off.

    Due to some commitments I am unable to fix for a few weeks. Any recommendation on a PVC glue that I could use temporarily until I replace the connection.
    Kenbob
    inground, 23,000 gallons, vinyl liner, sand filter, 2 speed Whisperflo 1.5 HP, gas heater

  4. #4
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    Re: Pump Loses Prime When Off

    Ken,

    It sounds like you are attempting pvc patching. PVC joints are a one-time put together and you typically cannot fix them by adding more pvc glue to the joint. Is that what you are asking?
    Dave S.
    Site Owner 42k vinyl and concrete pool, 1.5hp pump, 140gpm filter, No SWG
    TFTestkits owner
    TFTestkits , PoolMath , Pool School

  5. #5
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    Re: Pump Loses Prime When Off

    Yes as a temp fix due to other commitments until I can repair properly. Some say close all inbound pump valves use a vac on pump inbound to drawn PVC glue into the crack while there is a suction on the line
    Kenbob
    inground, 23,000 gallons, vinyl liner, sand filter, 2 speed Whisperflo 1.5 HP, gas heater

  6. #6
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    Re: Pump Loses Prime When Off

    Some say close all inbound pump valves use a vac on pump inbound to drawn PVC glue into the crack while there is a suction on the line
    In theory, you may have some success, but I doubt it. Certainly, prime the area first with pvc primer and cleaner.

    If you are attempting a temporary fix, I think I might try plain inexpensive latex caulk. Again, use PVC primer first and then put the caulk on and press it into the joint with your finger. I have never tried this so I have no idea it will work, but it will be easier to do and easier to clean up.

    This type of fix will ONLY work on the suction side of your system (if it works at all) You are spinning your wheels to try it on a pressurized joint.
    Dave S.
    Site Owner 42k vinyl and concrete pool, 1.5hp pump, 140gpm filter, No SWG
    TFTestkits owner
    TFTestkits , PoolMath , Pool School

  7. #7
    Mod Squad Bama Rambler's Avatar
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    Re: Pump Loses Prime When Off

    You might try some Pool Putty. Encase the whole joint in the epoxy. Leave the pump running as long as the container says it takes to obtain a full cure. I'd follow Dave's advice about using primer to assist the putty sticking better.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 1.5hp Dynamo pump. 24" Pentair Sand Dollar Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit
    You can stop SLAMing your pool when you pass the OCLT (You lose 1ppm or less FC overnight, & You have .5ppm CC's or less) & your water is clear.

  8. #8
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    Re: Pump Loses Prime When Off

    Thanks for all you input. I bit the bullet and replaced the PVC. Issue resolved. 1 or 2 bubbles the size of nickel on glass but no more and holding priming after pump stopped.
    Kenbob
    inground, 23,000 gallons, vinyl liner, sand filter, 2 speed Whisperflo 1.5 HP, gas heater

  9. #9
    Mod Squad Bama Rambler's Avatar
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    Re: Pump Loses Prime When Off

    Dave J. TFP Moderator
    24' x 52" Round AGP. 1.5hp Dynamo pump. 24" Pentair Sand Dollar Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit
    You can stop SLAMing your pool when you pass the OCLT (You lose 1ppm or less FC overnight, & You have .5ppm CC's or less) & your water is clear.

  10. #10
    Senior Member In the Industry

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    Re: Pump Loses Prime When Off

    Dave S.
    Site Owner 42k vinyl and concrete pool, 1.5hp pump, 140gpm filter, No SWG
    TFTestkits owner
    TFTestkits , PoolMath , Pool School

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