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Thread: Low pressure on DE filter, what could be the problem?

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    Low pressure on DE filter, what could be the problem?

    I got a 20,000gallon in-ground pool with a DE filter. Two weeks ago I had the DE from the filter cleaned out and recharged with "fiberclear" type stuff. Seemed to work great and the pressure reading on the filter looked in the normal 15psi range.

    A week later now I noticed the pressure reading on the filter is very low, maybe only 3psi. However the water flow looks OK on the pool side.

    Stopped the pump, opened the pressure release valve, fastened the loose looking anchor bracket, restarted the pump and close the valve after air has been blowing out. However the pressure is still low.

    What could be the problem? Could it be we put too little of the fiber clear stuff in originally ( the pool guy didn't really measure it) and what was there got leaked out, so that the filter is running empty without resistance now? Or a leak somewhere? Can't identify any obvious problem. I"m kind of hesitant to try anything the would potentially break things.

    Thanks

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    Melt In The Sun's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Generally, low pressure is caused by a blockage in the suction line or an air leak. You say there's good flow; is there a bunch of air bubbles in the pump strainer basket? Could anything big have gotten sucked down the skimmer?
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Mod Squad jblizzle's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Does the gauge still go to zero when the pump is off? Maybe the gauge went bad.
    Jason, TFP Moderator
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    Re: Low pressure on DE filter, what could be the problem?

    Thanks for the reply. The return flow looks visually normal, check it by holding my hand in front of water coming out of the return jet its not really obviously weaker. Didn't notice any bubbles in the return flow either.

    The skimmer had baskets installed that should have protected anything large getting stuck in the underground pipes. As a test I switched the pump between getting water from the pool and the spa, which are going to the pump via separate underground lines, and get the low pressure reading in both cases. The valve to switch is just in front of the pump, which is itself protected by a basket.

    I noticed some residual filter stuff on the ground below the filter, could it be really just the filter leaked the fiberclear stuff? It has been raining so its hard to tell how much is is. What that explain low pressure?

    Is it safe to run to keep running the pump before getting to the bottom of this? Thinking it could be damaged by running it with too much or too little load.

    Thanks for advising.

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    Mod Squad jblizzle's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    With DE .... I do not recall seeing much of a pressure difference between starting the pump and adding the DE (maybe a couple PSI). I would not think running with no DE or fiber would be that much lower of a pressure ... so something is clearly amiss.
    Jason, TFP Moderator
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    Re: Low pressure on DE filter, what could be the problem?

    The pressure gauge resets back to 0 when switching the pump off.

    One more detail, today I also noticed that the pool water level was low, almost getting close to the skimmer level, but I don't think the pool ever got below that level. Not sure if that created a problem. I topped up the water level now.

    I also seem to remember to have a hire pressure reading before adding any filter material, strange.

    I don't believe the pool guy did lubricate anything before putting the filter together, could there be a problem.

    Any chance the pump is bad? Just from the sound and look of it did it seemed normal?

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    Richard320's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Try flicking the gauge with your finger a few times while the pump is running.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Low pressure on DE filter, what could be the problem?

    Check the pump impeller for debris caught in it. A partially clogged pump will show up as reduced pressure at the filter, even though you can feel flow at the returns.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Low pressure on DE filter, what could be the problem?

    Strange thing today the pressure is back up to about 8-9 PSI, still less than the 15 psi I want to see, but double than yesterday. That's after switching the valves be between pool and spa a couple times, and also open and closing the bump basket. Can't figure out what made the difference.

    I also noticed when shutting the pump off water splashes back out of the lid that's above the pump basket. Does this indicate anything abnormal?

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    Melt In The Sun's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Nothing should come out of that! It sounds like the gasket in that lid is missing or damaged...open it up and take a look. It should be nice and round, free of grit and nicks, and lubed up with some silicone- or teflon-based lubricant (not petroleum-based!). If it needs replacing, a pool store should have them for a few dollars. That should fix your low pressure problem.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Mod Squad jblizzle's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Quote Originally Posted by dblko
    I also noticed when shutting the pump off water splashes back out of the lid that's above the pump basket. Does this indicate anything abnormal?
    My old pump did that too ... sprayed all over the place when I shut the motor off. But, when running, it never pulled in air. I guess the suction was enough to seal up the lid.

    So ... that could be a problem, but also may not be a problem.
    Jason, TFP Moderator
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    Re: Low pressure on DE filter, what could be the problem?

    Can't see anything unusual about the O-ring. Also I could not feel any debris inside the pump impeller opening by just checking with my and under water. (having first made sure the system and fuses are powered off).
    There is some sticker on the lid saying: "Attention, the cover "O" ring has been factory lubricated. Do not apply additional lubricant for pressure testing."

    By the way, can one upload pictures to the forum?

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    Mod Squad jblizzle's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Mine had that sticker too which applied to the initial installation ... you still need to lube it.

    Yes you can upload pictures to the forum (Use the Full Editor and add attachment) or upload them to a place like photobucket and post the link here.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Low pressure on DE filter, what could be the problem?

    Quote Originally Posted by dblko
    Can't see anything unusual about the O-ring. Also I could not feel any debris inside the pump impeller opening by just checking with my and under water. (having first made sure the system and fuses are powered off).
    There is some sticker on the lid saying: "Attention, the cover "O" ring has been factory lubricated. Do not apply additional lubricant for pressure testing."

    By the way, can one upload pictures to the forum?
    Is this a Hayward "Northstar" or Jandy "Stealth" pump? If so, they are notorious for partial clogs from pine needles; and you have to pull the motor and expose the impeller to clean them!
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Melt In The Sun's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Quote Originally Posted by jblizzle
    My old pump did that too ... sprayed all over the place when I shut the motor off. But, when running, it never pulled in air. I guess the suction was enough to seal up the lid.
    Hm, learn something new every day!
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Mod Squad jblizzle's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Quote Originally Posted by Melt In The Sun
    Quote Originally Posted by jblizzle
    My old pump did that too ... sprayed all over the place when I shut the motor off. But, when running, it never pulled in air. I guess the suction was enough to seal up the lid.
    Hm, learn something new every day!
    It was one of the Hayward RS pumps:


    The lid is only tightened on the sides, so the water would squirt out 90 degrees from the screws I guess because the lid was not as tight there ... pretty poor design in my opinion.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Low pressure on DE filter, what could be the problem?

    The label on the pump motor says AO Smith Hayward.
    Would running the pump with the current 10psi performance vs. 15 psi normal create a problem, having not yet identified the issue?
    I mean could it overheat or burn out?

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    Mod Squad Bama Rambler's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Running the pump at 10 psi filter pressure is fine. Mine runs about that all the time. Even if the impeller is partially clogged it's going to draw less amps.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: Low pressure on DE filter, what could be the problem?

    Thanks. Sorry for going on with this, what is the relation of amps drawn and mechanical work?

    What case draws a higher current, a motor that runs freely without mechanical resistance or one that runs against heavy mechanical resistance? It seems that the free spinning motor should draw less amps than the motor that spins against a heavy load. Is that right?

    I wonder what a clogged impeller means in terms of the mechanical work the motor works against? Is that the case where the motor works harder because something is stuck in the impeller that puts up more resistance against it spinning at normal speed? Or is this that case that the pump runs more freely without having to lift as much water as before?

    What about the case where one for example of trying to run the pump while the supply line is closed?
    Maybe my problem is really air in the supply line? I guess in this case the motor would draw air and see less or a mechanical resistance and thus draw less amps.

    Thanks

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    Mod Squad Bama Rambler's Avatar
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    Re: Low pressure on DE filter, what could be the problem?

    Centrifugal pumps are funny things. They draw the most current under the lowest head moving the most water. Raising the amount of head (pressure) causes it to work less and therefore draw less current.

    Air is easier to move and has more slip than water, so introducing any air into the system casues the pump to work much less and therefore draw less current.

    A clog in the impeller inhibits the pump from doing all the work it was designed for, and thusly reduces the amount of current draw.

    Our resident pump guru, Mark (mas985) has a pet peeve about "a pumps ability to lift water". Pumps don't lift water. They create a low pressure on the suction side and the atmospheric pressure forces the water toward the vacuum.
    Dave J. TFP Moderator
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