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Thread: Calculating flow

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    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Calculating flow

    I am still trying to get a handle on everything that came with the pool that came with the house, and one of them is how long to run the filter. I searched the forum and got horribly confused with pressure drop and loss of head and all that.

    So I thought about it and figured out a simple way. I moved the valves so I was drawing out of the spa and filling into the pool. I timed how long it took to go from spillway to top step. 9" in 3:30. The spa at that level has a diameter of 83". Then I just crunched numbers and came up with 60gpm. That equates to 3600gph, which means to get a full turnover, I need to run the filter 4½ hours/day. Hopefully this may help someone else in the same predicament.

    Right now it's 3 hours a day, plus extra hours when I'm fussing with the chemistry or just brushing. And it all makes sense. When I run it those extra hours it does look sparklier. (Is that a word?) So the timer will get some adjustment. Is there any reason I can't get a second set of pointers and run half in the max sun and the rest in the evening hours?

    I've already got the intake flows evened out; all it took was a diverter? - flying saucer looking thing - in the skimmer and some trial and error. Now if I sweep silt to the main drain, it gets sucked in! My next pumping experiment will be aiming the jets. I intend to make some zero buoyancy empty soda bottles and a good mix of empty ones and check currents in and on the water.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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

    Re: Calculating flow

    The ideal pump run time isn't actually based on the number of turnovers you have, that is just a handy rule of thumb. The ideal pump run time is based on water clarity and circulation and is best determined empirically, see this Pool School article. Of course it is nice to know the flow rate.

    Yes, getting an extra set of trippers for the timer so you can run the pump at two different times each day is a good idea.

    A good way to check circulation is with food dye. It takes a fair bit of dye though. I use those small squeeze bottles of liquid food dye sold in the baking isle. It typically takes an entire bottle, 1 oz, to get a good idea of the circulation. The dye more or less vanishes after five minutes and is totally broken down in less than a day. It may cause a slight increase in chlorine consumption, but the difference in chlorine consumption is very small and usually not noticeable.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

    Re: Calculating flow

    In commercial applications, they require a 6 hour turnover rate. We will take the gallons in the pool and divide by 360 (the minutes in 6 hours) to get a gpm rate, which then allows us to figure what size pump(s) are needed to fulfill that requirement. If residential pools are designed using these same specs then it is safe to say that they should be able to maintain water cleanliness similar to Health Department controlled bodies of water.

    I run my pump 8 hours a day, every day. Cheap insurance (I run a Hybrid pump, at about 2.2 amps) to have a clean pool, in my opinion. Stagnant pools gross me out; pools need to run to maintain cleanliness. I see people turn their pump run times down all the time and then wonder why they have a difficult time maintaining water cleanliness. The only "benefit" that comes from running a pump for shorter periods is a few dollars saved on the electric bill. Not worth it in my opinion.

    Your math and run times look pretty good to me. Another set of dogs on the time clock to break up the run times is definitely an option.


    Edit: Looks like I posted at the same time as Jason! Looks a little redundant in parts, but I'll post anyway

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