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Thread: Unusually Low Back Pressure

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    Join Date
    Apr 2009
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    Virginia Beach, VA
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    26

    Unusually Low Back Pressure

    I recently took apart my DE Filter to wash it out. After I put it back together, the back pressure was 10psi, which is about what it normally is after cleaning it, so I was happy. Recently, however, the back pressure has dropped. It's currently 2 psi. I've also noticed that the water is not reaching the top of the clear lid on the pump like it normally would. It only comes up to about a half inch to an inch below the lid. Does anyone know what the possible cause might be?

    I was out of town for about two months this summer and while I was gone, my wife asked a friend to come over to clean the filter for us. When I got back I asked him if he recharged with DE powder and he said he did not. I know this can cause damage, and when I took apart the filter I noticed a small tear in one of the grids where a small piece of debris was lodged in it. I had this happen once before (and have since replaced those grids), but that didn't cause low back pressure like I'm getting now. Do you think that may be the culprit this time?

    Thanks in advance for your help!
    Andrew - Virginia Beach, VA
    22,000 gallons; 16x32 rectangle; 3.5Ft-8Ft Depth; Pentair Whisper Flow 2 speed Pump 1.5/.5HP; Pentair FNSP60 DE Filter; Aqua Rite SWG. Polaris 180 cleaner.

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    37,879

    Re: Unusually Low Back Pressure

    No, the low PSI reading would be caused by something else.

    Low filter pressure usually means some kind of blockage on the suction side of the pump, or a failure to fully prime. Seeing air in the pump basket suggests trouble priming. Check to make sure all of the appropriate valves are open (if you have valves other than the main valve). Also, look to see that the water is high enough up the skimmer so there isn't a vortex forming that could draw in air.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Unusually Low Back Pressure

    From what I can tell, all of the appropriate valves are open and the water is about 2/3 the way up the skimmer, which is where I normally try to keep it. I took apart the filter, cleaned it, put it back together and recharged it with DE powder and still no change. There's barely any back pressure registering on the guage, so I'm not sure what to do. Do I need to call a repair man out to troubleshoot?
    Andrew - Virginia Beach, VA
    22,000 gallons; 16x32 rectangle; 3.5Ft-8Ft Depth; Pentair Whisper Flow 2 speed Pump 1.5/.5HP; Pentair FNSP60 DE Filter; Aqua Rite SWG. Polaris 180 cleaner.

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    duraleigh's Avatar
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    Apr 2007
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    Re: Unusually Low Back Pressure

    Do I need to call a repair man out to troubleshoot?
    Not necessarily. Do you have what seems like normal flow coming back into the pool or is it reduced?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    solarboy's Avatar
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    Re: Unusually Low Back Pressure

    I had similar problems on a pool with an unusually long suction line to skimmers (80 foot) and a 1/2 HP pump. Also the suction line dipped above water level at one point. We cured it by fitting a 1.5 HP pump.
    Self built 5500 gallon bare concrete (temporarily) pool with limestone coping, Pentair Swimmey 1/2 HP pump, Triton sand filter with DE, Simpool peristaltic muriatic acid pump with pH sensor and Monarch SWG. Home made solar heater with Pentair Compool control panel and 3 way valve. 1 skimmer, 1 main drain, 2 returns, 2" plumbing, Hayward auto fill valve.

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    Join Date
    May 2007
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    South Central NJ
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    Re: Unusually Low Back Pressure

    Check your pump basket. If it's cracked, I'd be willing to bet the impeller has debris stuck in it. With some pumps, you can reach the front of the impeller and pull out the clog while other may require the removal of a few bolts to split the front and back half. Also, before splitting the pump, check the lid gasket. A little debris there may be the cause too.

    Scott
    Owner of - PoolGuyNJ LLC
    Expert Pool and Spa Repairs, Renovations, and Augmentation. Helping people decide what is the right gear for meeting their needs. Expectations Set, Expectations Met, No Surprises.

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