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Thread: pumps in parallel

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    pumps in parallel

    When running pumps in parallel, do they need to be at the same psi?

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    JasonLion's Avatar
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    Re: pumps in parallel

    Welcome to TFP!

    psi isn't a pump specification, it is the result of the combination of a pump and a plumbing system.

    When running pumps in parallel they need to be matched pumps (same size, same design) with piping the same size and same length.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    mas985's Avatar
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    Re: pumps in parallel

    Pumps running in parallel have no choice but to run at the same PSI. The point where they combine has to be at the same PSI because it is a common node.

    However, you can run pumps in parallel of different sizes although the smaller pump will produce much less flow rate because both pumps see the same head loss that is created by both pumps. So the combined flow rate of both pumps is less than the sum of the individual flow rates when run separately.
    Mark
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    Re: pumps in parallel

    Ok thanks, the gauges on both pumps (which are the same size amp/volt and make) have guages that are reading differently. The first pump to pull off of the main pipe is reading 25 psi, the second off of the same pipe is reading 5-7 psi. My flow rate is about 1500-1700 when the butterfly valves are open about 50%. How can I correct the difference in psi.

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    asxetos's Avatar
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    Re: pumps in parallel

    The pumps might be the same in amp/volt and make (that is, they use the same motor) but one of them might be a pressure pump (high pressure with less flow) and the other might be a high flow pump (high flow with less pressure).

    Take a look at the impellers of these pumps if no flow/pressure chart is available.

    Assuming both are pressure pumps (or both are high flow pumps), then take a look at the geometry of the pipes feeding and exiting the pumps, until the point where these pipes meet, you should see a mirror image, leading to a Y connector (top of Y comes from each pump, bottom of Y is combined exit).

    Even better, post some pics.
    Donīt be fooled by the sheep on my bike, I swim with fish in my sound equipped pool.

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    JasonLion's Avatar
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    Re: pumps in parallel

    One or both of the gauges are broken. The pressure must necessarily be the same if their outputs are connected together.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    mas985's Avatar
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    Re: pumps in parallel

    Where are you measuring pressure in relationship to where the flows combine? Or do the flows never combine?

    If they are feeding different return pipes, then it doesn't matter.
    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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    Lershac's Avatar
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    Re: pumps in parallel

    Are their outputs connected together? Just making sure they are truly in parallel.

    If they both draw from the same intake system yet have different paths to the pool it is possible for the situation you currently observe to be normal and everything is working correctly.

    For example, main pump and a water feature pump that is plumbed separately from the filtration system.
    (DIY):16K Gal 20X30 rectangular IG Gunite, w/spa, CCP 520 filter,2 Pentair VS pumps, 400KBTU Pentair gas heater, Heat Pump for cooling, **update5.25.2013** added an intellichem with acid pump that will control existing SWG. My Build Thread Here

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