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Thread: low speed pump: double time not = high speed filtering

  1. #1
    Junior Member
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    low speed pump: double time not = high speed filtering

    I wish I'd found this site long ago....

    A few years back I replaced a dead motor with a 2-speed whisperflo (1.65 SFHP). I find that at low speed, even running 24 hr/day, I don't get good filtration. At high speed for 10 hrs/day I can. (One difficulty is that in summer my pool can get > 90 degrees.) I know the ancient 1.5" plumbing limits things, but I would expect it is better at slow speeds. Is there a maximum head or minimum pump rpm threshold causing me troubles?

    I tried this with both my DE and sand filters. I have both in parallel, as I found my sand didn't filter algae well enough. Now I just run my low speed pump constantly through the sand and a std. motor on a DE filter for some hrs in summer and to vacuum.

    Sand filter: Hayward 3.1 ft^2
    DE: Hayward EC75

    -Thanks for advice!
    33000 gal, unheated 40 yr old pool in SoCal
    solar cover to help evap & keep very toasty

  2. #2
    Senior Member blakej's Avatar
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    Feb 2012
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    Phoenix, AZ
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    Re: low speed pump: double time not = high speed filtering

    Hey Lotus, it actually sounds like the trouble may be related more to your filter(s) than your pump. True, your 1.5” plumbing is not doing you many favors these days, but honestly it sounds like your filter or water chemistry are the culprits for the filtration problems you’re seeing. To rule out the function of the pump, check these things:

    *Make sure your pump pot is full of water
    *Make sure there’s water coming out of the return line
    *Check suction in the skimmer

    If these three points pass, your pump is operating as it should.

    Now the filters: make sure you’re backwashing regularly. If you go too long without backwashing, the buildup is eventually just going to carry back into your pool, which may account for some of your trouble. Also, check the pressure readings on your filters – they should be no more than 10 PSI over the starting clean pressure (your owner’s manual will tell you what that is). Also, how old is your D.E. filter, and have you ever replaced the grids? They’ll need to be switched out about every 5-7 years, so that’s also something to consider.
    Hope this helps…

  3. #3
    Junior Member
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    Re: low speed pump: double time not = high speed filtering

    No, the filters weren't clogged and they work fine at full rpm. I just thought of another idea I have never seen discussed: What if the same volume is run through the pump in the full & half speed cases, but at low speed just the surface water circulates? Thus high speed creates the turbulence to mix up the water.

    I may have a small leak in the input as I do get air in the pump basket. At low speed I see some flow out of the nozzles but have never tried to measure flow rates.
    33000 gal, unheated 40 yr old pool in SoCal
    solar cover to help evap & keep very toasty

  4. #4
    Senior Member In the Industry

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    Raleigh, NC
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    Re: low speed pump: double time not = high speed filtering

    as I found my sand didn't filter algae well enough.
    Their is no filter or pump of any type that will filter out algae from a pool.

    If that is the issue you are trying to solve, you must correct your water chemistry so that algae doesn't grow.

    Do not expect your filter(s) to get rid of live algae at any speed.
    Dave S.
    Site Owner 42k vinyl and concrete pool, 1.5hp pump, 140gpm filter, No SWG
    TFTestkits owner
    TFTestkits , PoolMath , Pool School

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