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Thread: Need help with filter size.

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    Need help with filter size.

    OK so I manage a small apartment complex that has a pool. The De filter is getting to be a pain in the butt, especially now when we just opened the pool and are trying to get it ready for the season. So Im ready to swap it out for a sand filter. It being a commercial pool differs the requirements a bit compared to a residential pool. Im required to turn over water more often (technically 4 times a day) Its about a 50k gallon pool averaged out between the deep and shallow and the 925 lb filter says its can turn over 101k gallons every 12 hours according to the pentair specs, so that would be perfect. But the dealer is afraid the pump doesn't have enough GPM to properly back wash a filter that large. Is this really a concern? Its 3" suction and 2.5" return plumbing, 20x50 pool with a 10 foot deep end, 3 hp pentair variable pump powering the system. I have no idea what the GPM is of the pump. But I would think a 3 hp pump would be powerful enough to backwash the filter. The plumbing only has 2 90* bends. So Help me out, is it over kill to put in a half ton sand filter. The dealer is recommending a 500 or 600 pound filter. But I thought with filters the bigger the better. Im just trying to reduce the required maintenance. This being a rental the less maintenance the better, so I'm not out there every week pressure washing a de cartridge getting my self covered in green slime. Thanks so much!

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Need help with filter size.

    Worst case you might need 105 GPM to backwash a 900 lb filter. The actual GPM you get from a 3 HP pump varies depending on a number of factors, not all of which you have listed, still the odds are that you are getting at least that flow rate. For a commercial pool you often need to formally document that the flow rate is sufficient, something more solid than my educated guess.
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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Need help with filter size.

    The Intelliflo will deliver about 100 GPM on Curve-C which is typical of 2" plumbing. Given that you have larger plumbing and that backwash mode bypasses most of the return side plumbing, I would say that there should be no problem reaching backwash flow rates of over 105 GPM.
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