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Thread: Dirty filter, major loss in water flow.

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    Aleforge's Avatar
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    Dirty filter, major loss in water flow.

    This is going to be a really stupid question, but being winter with the pool closed up I was just thinking about it today and figured I would ask. My old pump burned up last september, I ended up having to replace it. This got super involved, old wiring was dry rotted, plumping wouldn't match up, etc. I replaced my old generic pump with a Pentair of the same HP. The filter was extremely dirty, my PSI over the summer was around 6-8PSI, and by the time I got it back running (a few weeks after it went down) it was up around 25-28PSI. I am guessing sitting around drying out didn't help...

    So long story short I needed to vacuume my pool before closing it and noticed very low suction. I could tell it was bad when I dropped the vacuum into the skimmer I could pull it out myself with it on.

    I thought at the time that when the PSI went up it meant the water needed more pressure to keep flowing at a normal rate. But now I am not so sure. I am buying a brand new filter before opening this spring and hoping that's all it is. I am worried if its not the filter I should of went up to a larger pump.

    Thanks!
    In ground (installed 2000), fiberglass, cartridge filter, Pentair Super Flo Single speed pump (2014).

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    JasonLion's Avatar
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    Re: Dirty filter, major loss in water flow.

    When you change pumps, it is common for the "clean" filter pressure to change. The new pump is rarely exactly the same as the old pump, so it will have a different pressure reading when the filter is clean. A larger pump means a higher "clean" filter pressure, and smaller pump would mean a lower "clean" filter pressure. The listed HP of the pump is only a rough guide to how large the pump is. Pumps of the same HP can vary dramatically in their actual power.

    If you are going to close the pool, or leave the pump off for weeks, you should clean the filter beforehand if at all possible. Obviously if the pump breaks you can't literally clean the filter beforehand, but you should clean it as soon as you figure out that the pump won't be working again right away.

    When the filter pressure goes up 25% or more from it's "clean" pressure, you should clean the filter.

    The filter pressure goes up because there is increasing resistance to flow. As that happens the flow rate declines (more resistance means less flow).

    Chances are that the filter pressure went up both because the filter drying out created more resistance to flow, and the pump got larger.

    Unless there is something you haven't mentioned, there is no reason to buy a new filter. At the worst you might need a new filter cartridge. Even that should wait on seeing how the filter behaves after it is cleaned throughly.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Aleforge's Avatar
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    Re: Dirty filter, major loss in water flow.

    Jason,

    First of all thanks for responding!

    I understand what you mean in regards to the pressure buildups. But does it mean no matter how much pressure builds up I should still be getting the same amount of overall flow?

    Cleaning wise, I don't have a way to backwash the filter. But your saying I should just clean it myself instead of buying new? I only came to that conclusion because it looks really dirty and the previous homeowner said he had to replace one every 2 years. Sorry I meant cartridge!

    Thanks!
    In ground (installed 2000), fiberglass, cartridge filter, Pentair Super Flo Single speed pump (2014).

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    Mod Squad jblizzle's Avatar
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    Re: Dirty filter, major loss in water flow.

    For a given pump/plumbing/pool setup, if the filter pressure rises, then the flow rate is going to drop. I am not sure I understand your question.

    You should be opening up the filter and cleaning the cartridge whenever the filter pressure rises 20-25% over the clean pressure. You give no indication of your pool size or the filter size in your signature, so no way to even guess how often that may be required. Generally it is needed every few months if your pool is clean. If you get algae, then you may be cleaning it every few hours.

    Without knowing the history of your existing cartridge, I might consider replacing it and then using the new pressure as your "clean" pressure.
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    Aleforge's Avatar
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    Re: Dirty filter, major loss in water flow.

    Sorry J,

    I wasn't sure if I explained my question properly. I guess the short version would be, if my filter is extremely dirty and the systems PSI is high would that make the actual flow through the system less. I thought maybe the PSI going up meant its taking more force to push the water through to keep it at the same flow rate. I swapped pumps, but it took a few weeks because of the can of worms I opened. Which I doubt helped the filter out. Fired it back up to clean so I could close it and the vacuum was getting much less suction than before. As well as the low return jet rate.

    This kind of worried me that the new pump wasn't working well.

    The current cartridge has been in the pool for two seasons now. I have a huge hairy dog (Newfoundland) and she sheds balls of fur that blow into the pool. I had a few algae build ups. Didn't clean the filter once this season but the PSI stayed pretty low until late summer when it was slowly rising. I am a new pool owner, I had no idea you were suppose to wash the filters on a regular basis.
    In ground (installed 2000), fiberglass, cartridge filter, Pentair Super Flo Single speed pump (2014).

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    JayBauman's Avatar
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    Re: Dirty filter, major loss in water flow.

    Pressure drop across your filter media (i.e. what you measure on the pressure gauge) is a combination of many factors, including cleanliness of your filter and the flowrate of water through your system. Therefore, you can't attribute changes in your pressure reading to filter cleanliness alone.

    Pump manufacturers have gotten better at design and manufacturing over time. Today's 1.5HP pumps can move the same amount of water as yesterday's 2.0HP pumps.....all while useing 25% less electricity. It's quite plausible that you replaced your old pump with a new one of same HP rating, but in fact the new one is capable of moving significantly more water. This would increase pressure drop across your filter, which would show up as higher pressure on the gauge.

    Anytime you make major changes to your pool plumbing, you should throw away all your historical pressure points and start over again. Install a new pump, clean the filter media, and read the pressure. This is the new "clean" pressure. When the number raises about 25%, it's time to clean your filter.

    I might have missed it....do you have sand, cartridge, or DE filter?
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    JasonLion's Avatar
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    Re: Dirty filter, major loss in water flow.

    Yes, a dirty filter will reduce the flow rate. A very dirty filter will reduce the flow rate dramatically.

    There is one pump, the IntelliFlo VF, that can maintain a constant flow rate up to a very high filter pressure, if configured to do so. Unless you have that pump setup to do that feature, your flow rate will fall as the filter pressure goes up. We don't recommend using that pump in that way, as the filter pressure will go up very rapidly as the filter gets dirty which causes extra stress on the system. Even with the IntelliFlo VF, if you don't clean the filter soon enough the resistance to flow will eventually get so high that it can't maintain the flow rate.

    You have two issues mixed up together, a new pump and a dirty filter. With the information available it is impossible to tell what state the pump is in vs just how dirty the filter is. My presumption is that the problem is the filter being dirty, and the pump is fine. What you have described is sure to have made the filter very dirty, and that alone would be enough to cause everything. But it is impossible to be sure of that until the filter is properly cleaned.

    JayBauman, signature says cartridge filter.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Aleforge's Avatar
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    Re: Dirty filter, major loss in water flow.

    Guys I really appreciate the help! I am going to cross my fingers that this all falls on the dirty cartridge.
    In ground (installed 2000), fiberglass, cartridge filter, Pentair Super Flo Single speed pump (2014).

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    Mod Squad jblizzle's Avatar
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    Re: Dirty filter, major loss in water flow.

    Yup, get a new cartridge installed and then report back. You could try to clean your existing cartridge and use it as a backup, but as neglected as it sounds, it may be permanently clogged.

    Take a look at this article: http://www.troublefreepool.com/threa...rtridge-filter

    And please add more pool and equipment details to your signature as described HERE as it will help us help you.
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    Mod Squad woodyp's Avatar
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    Re: Dirty filter, major loss in water flow.

    Quote Originally Posted by Aleforge View Post
    Guys I really appreciate the help! I am going to cross my fingers that this all falls on the dirty cartridge.
    Almost guaranteed!
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