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Thread: Maximum GPM For 1.5" Pipe

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    ChuckDavis's Avatar
    Join Date
    Aug 2010
    Durham, NC

    Maximum GPM For 1.5" Pipe

    I just upgraded my Hayward SuperPump with a variable speed motor and 2.5 HP impeller. (See

    In Hayward's documentation for the SuperPump VS they recommend a maximum 45 GPM flow rate for 1.5" pipe.

    My new pump has a button to speed the pump up to maximum RPM for vacuuming, but at max speed it is putting out 65-70 GPM.

    Is the 45 GPM recommendation a "don't blow up your system" limit or am I safe to run at 65-70 GPM for vacuuming and backwashing? If 65-70 GPM is too high, is there a GPM flow rate between 45 and 65 that is safe?
    15,000 gallon IGP, epoxy surface, waterfall, borates (!), not closed in winter
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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Maximum GPM For 1.5" Pipe

    You can run it as fast as you want. Not sure where they got 45 gpm but it there is no reason for it that I can think of.

    Pool pumps commonly push 60-80 gpm through 1.5" pipe.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Maximum GPM For 1.5" Pipe

    The particular filter wants 45-60 GPM when backwashing, and that range should also be just fine or even perhaps a little much when vacuuming.

    There is no specific flow limit, but as the flow rate gets higher the system gets less efficient. 45 GPM is a suggestion of the max flow rate for reasonable efficiency, but that is just an arbitrary suggestion.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  4. Back To Top    #4

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Maximum GPM For 1.5" Pipe

    See Maximum Flow Rates for PVC Pipes for more info. As Dave and Jason noted (posted around the time I was writing this), there really isn't a maximum, though it becomes very inefficient to use such narrow piping for higher flow rates since pump sizing and energy costs go up dramatically.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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