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Thread: DE Filter: low pressure in filter & slight leak after cleaning

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    Question DE Filter: low pressure in filter & slight leak after cleaning

    Hi!
    I have a Pentair FNS 36 Plus DE filter for an in ground pool. Last weekend I cleaned the DE and replaced it making sure to lube the O Ring and tap the band connecting the two halves of the filter tank while tightening.

    When I restarted the pump I noticed a small trickle of water coming from the back of the band that holds the two halves of the filter together. I also noticed that the pressure gauge on top of the filter was pretty low (~4 psi). I vented the filter tank of all air, waited a few seconds and found there was more air to vent. It seems that water is seeping out and air is seeping in.

    I took the filter tank apart and inspected the O Ring - it looked ok - I re-lubed it and reinstalled it and put the band back on. When I restarted the pump I see the exact same behavior - small leak, low pressure, air in the filter tank.

    I hope it is just a bad O-Ring but it looks ok to me - is there anything else I should look for before ordering a replacement? I read related threads in this forum and have checked the ORing in the pump basket and have looked for any obstructions - none are obvious. Also of note is that there is good suction at the skimmer so the pump appears to be working well. Thank you for any advice you can give!
    Rinkelhause

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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Update:
    1. I tried disconnecting the kreepy krawly and running the pump just pulling water from the skimmer. The pressure in the DE Filter tank went up to 15psi and there did not seem to be any leak! Is it possible the leak is being caused by low pressure? Does the high pressure in the DE Talk cause the O-Ring/Seal to become more effective?
    2. Decided to order the new O-Ring since I cant think of anything else to do - will try install it today when it arrives and will update this thread.

    Any thoughts? Anything I am missing?
    Thanks!
    R

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    Richard320's Avatar
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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    My guess is that the two tank halves are slightly deformed, which is why they're difficult to get back together.

    Restricted intake - the vacuum and all that hose - means lower pressure. If there's a tiny gap somewhere between the two halves, it leaks. With higher pressure, the tank halves spread and close the gap and no more leak. Go stare at the filter with the pump off and watch it when you flip the pump on. You'll see the thing sort of shudder when the pressure is on. And you can also imagine how high that lid would shoot if the clamp wasn't there to hold it on.

    A new O-ring would be my first step. Clean all the seating surfaces well and grease up everything that slides together. And if there's any kind of sun fading, anything that tells you how the two halves were aligned before when it didn't leak, try to match that.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Mod Squad JohnT's Avatar
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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Your filter is pressurized with water, so it can't leak air while the pump is on. Your air leak is happening someplace before the pump impeller, which is right after the water flows out of the pump basket. A likely spot is the lid of the pump basket strainer.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Richard320, Thanks for that advice! I will replace the O-Ring and see if I can find any sun fading on the tank that would indicate warping. It doesnt seem to be deformed, when I mate the two halves on the O-Ring I am able to turn the top and it glides smoothly on the lubed O-Ring. All the equipment is in a shed so it is protected from the elements. I will look for that shudder the next time I turn it on and will report back.

    JohnT, Thanks for the help! I will see if I can find that air leak - I read the suction side air leaks page (Pool School - Suction Side Air Leaks) and will use that to try find out where that is happening.

    Will update status later today. Thank you both for the help - much appreciated!
    Rinkelhause

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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Update:
    1. On my lunch break I was able to look at the filter tank and turn on the pump - I did not see any shuddering. I also inspected the top and bottom for warping and could not find any evidence of that. The O-Ring arrived so I will get to install it later today.

    2. I took the pump basket strainer lid off and inspected, cleaned and lubed to O-Ring to ensure a good seal. After putting it back together and running the pump no change. Here is something I observed that I did not report before: When I run the pump, there is 2 inches of air at the top of the pump basket strainer. When I turn the pump off, this immediately fills back up with water. From reading the Suction side leak page I assume this is my problem.

    The leaking O-Ring in the filter is just a side effect of the low tank pressure. Does this sound right?

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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Update:
    1) Installed new DE Filter Tank O-Ring. After startup there was no change in behavior - still a small leak, air in the pump strainer and low pressure in the DE Tank (~4psi)

    2) I tried waving a burning incense stick around the pipe that comes from the pool to the pump and could not locate any air leak (I saw a youtube video where the smoke gets pulled into any holes/cracks that are sucking air)

    3) I just remembered seeing a small bit of water where the pump motor meets the pump strainer assembly (they are bolted together) when the system was shut down/started (catnt remember which) a couple of weeks ago. I cant seem to get it to happen again by starting/shutting down the pump but this could indicate a source for air entering the system right? I plan to unbolt the motor from the pump strainer assembly to see if I can spot a bad gasket/o-ring (I assume there must be one). If that does not turn up something the only other possibility is an in ground pipe air leak so I may add some PVC to bypass the existing route to test that theory, although that is the nuclear option.

    Does this sound like the right way to go? Any other advice would be greatly appreciated,
    Thanks!
    Rinkelhause

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    Re: DE Filter: low pressure in filter & slight leak after cleaning

    Update:
    Over the weekend I tried numerous things but the problem is still present:

    - Replaced Filter Basket O-Ring
    - Replaced whisper flow Gasket
    - Replaced whisper flow pump O-Ring
    - Replaced whisper flow shaft seal
    - Caulked around pipes leading to the Pump (obviously a temporary fix but aimed at diagnosing the source of the air leak)

    There is an interesting symptom though: when I open the jandy valve that pumps water coming from the filter tank up to the solar heating system on the roof the pressure in the DE Filter tank goes up and the amount of aim in the pump filter basket is reduced! Is is possible there is a lack of back pressure in the system?

    One last thing I can try is replumbing the pipe coming from the ground to the pump. Any other suggestions?
    Thanks,
    R

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