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Thread: pump size adequate for backwashing sand filter

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    pump size adequate for backwashing sand filter

    hi folks, i want to use a very small pump, run continually for my tub. i have a lower-threshhold flow switch to replace the one in the heater. however, not sure about the pump size yet. doesn't it take more pressure to backwash a sand filter than to clog it up in the first place? how much more pressure, and what does this mean for pump sizing?

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    Re: pump size adequate for backwashing sand filter

    What type and hp pump, what filter, and your changing a pressure switch in the heater? What type of heater.

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    Mod Squad jblizzle's Avatar
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    Re: pump size adequate for backwashing sand filter

    Welcome to TFP!!!

    I do not understand what type of spa and equipment setup you have. Please add your location (City, State or City, Country) to your profile and pool details to your signature as described HERE as it will help us help you.

    Standalone hot tubs usually have a 2-speed pump and cartridge filter ... so I am guessing this is not what you have?

    Are you not intending to have jet action any more?
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    Re: pump size adequate for backwashing sand filter

    hi folks, thanks for responding. i am building a tub setup with no jets from scratch. the heater i have is a raypak gemini 3 from the '80s and am shopping for a sand filter and pump now.

    rather than a 1/2 HP pump that runs occasionally, i've been looking into a much smaller circulation pump (1/10 HP for example) that would run continually. the reason is noise: the equipment is beneath our bedroom. location is SF, CA if it makes a difference. multispeed is definitely a desirable feature on the pump motor.

    my question is: how much pump do i need to be able to backwash the sand filter? i've only used cartridges in the past.

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    Re: pump size adequate for backwashing sand filter

    Welcome to the forum Bricktron

    You have three variables you would need to narrow down some to get an answer. There is a minimum HP you'll need to spin the pump but there is also a minimum of GPM the pump will need to be able to push through the filter to properly clean it and then there is the minimum GPM the filter requires. Since you are trying to go with the smallest motor you can, then you need to find out the requirement of the filter first, then a pump that meets or exceeds it's GPM requirements and a motor that will drive the pump.

    Would be helpful if you added your info to your signature.
    '70s IG Vinyl 32K gal, Lazy L, Hayward SuperPump 1.5hp 120V, S240 Sand Filter W/DE
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    Re: pump size adequate for backwashing sand filter

    all right, i put a little info in the signature though i had to keep it vague since i am still buying the equipment

    i understand that filters are rated for minimum GPM for filtration. if there is a second minimum GPM for backwashing which is a multiple of the first, that's the number i need to target with the pump's high speed. i bet this all probably means using a small filter, like a 12" one, but i should get my hands on the manual for one to read its specs.

    thanks folks!
    plumbing up wall-mounted equipment and plenty gauges below a 500G wooden outdoor hot tub.

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    JasonLion's Avatar
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    Re: pump size adequate for backwashing sand filter

    15+ GPM/square foot of sand surface area is typically required for backwashing.

    The best solution is a two speed pump. That will give you high speed to backwash the filter and low speed (1/8th the HP) for circulation.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: pump size adequate for backwashing sand filter

    Two speed would be great to have the quietest running pump under your bedroom and yet be able to backwash the filter when needed
    '70s IG Vinyl 32K gal, Lazy L, Hayward SuperPump 1.5hp 120V, S240 Sand Filter W/DE
    Solar Blanket, Well Water, Borax Added, TF-100 tester. ? too cold
    1979, 275gal Conway Emerald Spa P-100-2, ES-2 Spa Pack, bromine floater, indoor
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    Mod Squad jblizzle's Avatar
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    Re: pump size adequate for backwashing sand filter

    Just to add, running the pump continuously is rarely if ever required. The easiest way to save money on electricity is to not run your pump as much. I would suggest something in the 1HP 2-speed range and run on low for heating/circulation and on high for jets and backwashing.
    Jason, TFP Moderator
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    Re: pump size adequate for backwashing sand filter

    you all are great, one speed for each mode seems like how it should work. props to JasonLion for providing a number. now i can see about how strong the pump should be!

    jblizzle, i like the continual idea because it is the simples way to achieve rapid response time for temperature drops at any time, which really matters in night visits to a hot tub. my dad's tub pump is on a timer with manual override buttons (they are funny air switches), but using that is too complicated. the alternative is adding a low-voltage circuit linking a sensor right in the tub with a switching relay to turn on the pump, which is even more complicated, but as you say, it sure would save some power.

    say i did want to continually turn over 500G three times a day, which means a rate just over 1 GPM, and had a round 14" filter of just over 1 ft^2 area. regular circulation would see 1 GPM/ft^2, and in order to get 15 GPM/ft^2 for backwashing i'd need a second speed (or a second pump) 15 times as powerful. that's nuts, so i can see that i'd have to get a way larger pump or use a way smaller filter. exactly what i need to know before buying things. cheers!
    plumbing up wall-mounted equipment and plenty gauges below a 500G wooden outdoor hot tub.

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    Re: pump size adequate for backwashing sand filter

    You almost certainly don't need a variable speed pump. But they can generally have even lower flow than a 2 speed. And since you are a PG & E customer you get a rebate if you install a vs pump!!!!!

    http://www.pge.com/myhome/saveenergy...earchvariable/
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    mas985's Avatar
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    Re: pump size adequate for backwashing sand filter

    Why don't you just stick with a cartridge?

    -Better filtering
    -No backwashing
    -Less water wasted (CA drought)
    -Can be sized for very infrequent cleaning (I clean mine once per year)
    Mark
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    Re: pump size adequate for backwashing sand filter

    mas985, i have always disliked washing the cartridges, but you make a good case. does anyone put a multiport valve on a cartridge filter to facilitate filling and draining? also, would it just rip if i did gently backwash it?

    gwegan, good call. continuous variability on a pump would be sweet. the PG&E rebates say they are just for pool installations but perhaps the claim could be made anyway.

    thanks everyone for your advice!
    plumbing up wall-mounted equipment and plenty gauges below a 500G wooden outdoor hot tub.

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    mas985's Avatar
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    Re: pump size adequate for backwashing sand filter

    It takes me about 10 min per cart to clean once a year. Not a big deal. A multiport valve lowers efficiency by a lot so not worth it.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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