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Thread: Flow rate

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    Flow rate


    I work for a hotel that has a pool.. My local health department has asked that I come up with a formula to determine the actual flow rate for my pool.. I don't currently have any flow meters at all..

    I know how to determine what my flow rate should be as per state code..

    I just have no clue how to determine what it actually is... She did mention something about using motor size to determine the flow rate..

    Anyone know of the formula I would need to use?


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

    Re: Flow rate

    Welcome to TFP!

    You need to start by finding the pump curve for your pump. This is a chart that shows what the flow rate is for different amounts of total dynamic head (TDH). Then you need to try and figure out the TDH by making a detailed chart of your plumbing system with a list of all the fittings and pipe lengths. Doing this well enough to satisfy a health inspector is often a fair bit of work an can get rather complex.

    For a commercial pool this should all have been done when the pool was originally built, and you ought to be able to find the existing documentation.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    spishex's Avatar
    Join Date
    Oct 2008
    Hillsborough, NC

    Re: Flow rate

    You need to know the make and model of your pump along with the suction and pressure side pressure readings with the filter clean. You can use the pressure gauge on your filter (assuming it's working) for the pressure reading. You'll need a vacuum gauge for suction side (connected to the drain plug threads on the suction side of your pump).

    With the two pressure readings you can calculate your total dynamic head for the system, and with that you can look at the pump curve for your model which will tell you what your GPM should be.

    In a commercial setting like yours you should just have the boss spring for a flow meter and be done with it.

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