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Thread: Low Pressure in Return when set to Filter

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    Low Pressure in Return when set to Filter

    I've read some previous threads concerning this topic but still can't get my problem fixed. I have a Doheny's 1.5 hp pump hooked up to a hayward sand filter. When the multiport valve is set to filter the return pressure is very low, but if it is switched over to recirculate then the pressure is fine. I have tried backwashing the filter and priming the pump again, but all was to no avail. Has anybody else had this experience.

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    Richard320's Avatar
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    Re: Low Pressure in Return when set to Filter

    Sounds like the sand is hardened into a brick. Have you ever used any clarifiers or flocculents? I'd try Deep Cleaning a Sand Filter to break up the clods.
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    Re: Low Pressure in Return when set to Filter

    I assume you mean there is very little circulation in the filter mode (filter psi would be high), right?
    Dave S.
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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by duraleigh View Post
    I assume you mean there is very little circulation in the filter mode (filter psi would be high), right?
    Yes that's what I mean.

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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by Richard320 View Post
    Sounds like the sand is hardened into a brick. Have you ever used any clarifiers or flocculents? I'd try Deep Cleaning a Sand Filter to break up the clods.
    The sand is actually only a year old, it was just replaced last year and no chemicals except for chlorine have been used in it. Would it have had time to harden in a year?

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    Mod Squad jblizzle's Avatar
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    Re: Low Pressure in Return when set to Filter

    I think it would be good to open up the filter and inspect the sand:Deep Cleaning your Sand Filter
    That would rule out the sand itself.
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    Re: Low Pressure in Return when set to Filter

    I think it is definitely something to do with the sand because I backwashed it again today. The return line had very good pressure after backwashing, but after a few hours the pressure has dropped off again. Looks like its going to need a deep cleaning.

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    Mod Squad jblizzle's Avatar
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    Re: Low Pressure in Return when set to Filter

    What does your water look like? Maybe the filter is just doing its job.
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    Re: Low Pressure in Return when set to Filter

    After you run for a while does the psi get higher or lower? If the pressure "dropped off" then the psi would be lower
    Dave S.
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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by jblizzle View Post
    What does your water look like? Maybe the filter is just doing its job.
    Water is crystal clear now but it wasn't a week ago. We had an algae bloom that I'm just now getting under control.

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    Quote Originally Posted by duraleigh View Post
    After you run for a while does the psi get higher or lower? If the pressure "dropped off" then the psi would be lower
    Pressure is higher but flow out of the return is lower. I wasn't thinking when I said the pressure dropped off, I just meant the flow did.

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    Mod Squad JohnT's Avatar
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    Re: Low Pressure in Return when set to Filter

    How long do you backwash the filter?
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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by JohnT View Post
    How long do you backwash the filter?
    I just backwashed it until the water coming out of the waste was clear. Probably around 3 minutes and then rinsed for 1 minute.

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    Re: Low Pressure in Return when set to Filter

    How did you "get control of the algae"? Are you following the SLAM process? Passing the OCLT?
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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by jblizzle View Post
    How did you "get control of the algae"? Are you following the SLAM process? Passing the OCLT?
    I used the SLAM process. I shocked it with bleach and then continued to keep chlorine at shock levels until water was clear. It's actually still at shock level but I think I'm going to let it come back down now because the water looks very good.

    I'll probably do the OCLT tonight.

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    Re: Low Pressure in Return when set to Filter

    The filter is still just filtering out dead algae. Keep backwashing when pressure rises 20-25%.
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    Re: Low Pressure in Return when set to Filter

    Letting the pressure rise makes the filter a better filter filtering out smaller particles. The dirt accumulated helps the filtering process.
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    Re: Low Pressure in Return when set to Filter

    Quote Originally Posted by Hayward Pool View Post
    Letting the pressure rise makes the filter a better filter filtering out smaller particles. The dirt accumulated helps the filtering process.
    So the accumulating dirt is kind of a poor mans DE ? How high should you let the pressure rise ? The same 20 - 25 % ?
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    Mod Squad jblizzle's Avatar
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    Re: Low Pressure in Return when set to Filter

    The 20-25% is always the TFP recommendation.
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