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Thread: Very low pressure, suction seems to be working great.

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    Very low pressure, suction seems to be working great.

    I just moved into this house and replaced the broken old pump with a new pentair variable speed. So this will be my first time reading the pressure gauge. All the pipes are 2". I cleaned the DE filters thoroughly by taking them out. . At 2000 rpm, the psi is at 1-2psi only! The skimmer is doing a great job so i highly doubt the suction lines are blocked. I dont have a check valve either. Even if i switch to the drain, its still at 1-2psi. I even changed the gauge to make sure thats correct and made sure nothing was blocking the path way to the gauge. I have 4 return jets (3 in the pool, 1 in the spa) and if i switch the valve to the spa, i have 4 return jets in the spa.. IS it possible that this system is very efficient?? If i lower the rpm of the pump, its pretty much at 0-1psi. If i make it at 3000rpm, i can get it up to 7psi.. Is there any harm in having a low pressure system?
    At my previous house after I clean the filter, the pressure would be around 12-13psi which is normal.

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    Mod Squad zea3's Avatar
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    Re: Very low pressure, suction seems to be working great.

    I have a 1 hp 2 speed pump. At low speed the pressure barely moves off 0. On high speed it is around 10. As long as you are getting good flow into the skimmer and out of the return you should be fine. Your water will filter more efficiently at low speeds and subject the filter to less wear and tear.
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    mas985's Avatar
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    Re: Very low pressure, suction seems to be working great.

    Pressure seems a little low to me. On a typical pool with three suction lines, 2" plumbing and 4 x 1" eyeballs, at 3000 RPM, pressure should be around 15 PSI. A couple of questions:

    What is the filter pressure at full speed?

    How high is the pump relative to the water level?

    How many suction lines do you have pool to equipment pad?

    How many return lines do you have equipment pad to pool?

    How many return eyeballs are there?

    What type/model backwash valve do you have?

    Do you have a heater?
    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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    Re: Very low pressure, suction seems to be working great.

    Quote Originally Posted by mas985
    Pressure seems a little low to me. On a typical pool with three suction lines, 2" plumbing and 4 x 1" eyeballs, at 3000 RPM, pressure should be around 15 PSI. A couple of questions:

    What is the filter pressure at full speed?

    How high is the pump relative to the water level?

    How many suction lines do you have pool to equipment pad?

    How many return lines do you have equipment pad to pool?

    How many return eyeballs are there?

    What type/model backwash valve do you have?

    Do you have a heater?
    I just tested it out at 3000rpm to match your speed.
    11psi when skimmer is 100% on and 100% pool return jets.
    8psi when its 50/50 (drain&skimmer) and 50/50 (pool&spa jets)
    5.5psi when skimmer is 100% and 50/50 (pool&spa jets)

    At 2000 rpm
    2psi when skimmer is 100% on and 100% pool return jets.
    0-1psi when its 50/50 (drain&skimmer) and 50/50 (pool&spa jets)
    0psi when skimmer is 100% and 50/50 (pool&spa jets)

    I don't have a heater.
    I have (2) 2" suction pipes to equipment pad and I have (2) 2" return pipes from pad to pool.

    The 2 drains (spa&pool) and the skimmer pipes are all 2"
    The return jets are all 1"
    I have a hayward DE-4800 filter with no backwash valves or anything fancy, and a brand new pentair variable speed 3hp pump.
    I don't have a check valve.
    The pump/filter sits 22inches above the pool water line. The spa sits 7inches above the pool water line.
    I have 4 return jets to the pool (3 in the pool, 1 in the spa) If i switch the valve to the spa, i have 4 return jets to the spa. Combined I have 8 return jets.

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    mas985's Avatar
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    Re: Very low pressure, suction seems to be working great.

    I have a hayward DE-4800 filter with no backwash valves or anything fancy
    How do you backwash the filter?

    Anyway, the extra information on operation was helpful and explains the low PSI:

    Pump elevation will drop the pressure by 1 PSI for any speed

    No backwash valve means less head loss which lowers pressure

    A closed off a suction port increases suction head loss which reduces flow rate and drops pressure

    Multiple return pipes reduces return head loss and thus drops pressure

    So combining all of those will drop pressure a lot. Filter pressure should be at it's highest when the suction is set to 100/100 (both fully open) and pool return only.
    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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    Re: Very low pressure, suction seems to be working great.

    Quote Originally Posted by mas985
    I have a hayward DE-4800 filter with no backwash valves or anything fancy
    How do you backwash the filter?

    Anyway, the extra information on operation was helpful and explains the low PSI:

    Pump elevation will drop the pressure by 1 PSI for any speed

    No backwash valve means less head loss which lowers pressure

    A closed off a suction port increases suction head loss which reduces flow rate and drops pressure

    Multiple return pipes reduces return head loss and thus drops pressure

    So combining all of those will drop pressure a lot. Filter pressure should be at it's highest when the suction is set to 100/100 (both fully open) and pool return only.
    I always take the filter lid out to clean the grids. Even at my old house that had a multiway valve, i never used the backwash setting. I wasnt sure how much DE gets taken out when I backwash so instead I got into the habit of taking the lid off.
    BTW, when i mean "50/50"=100, (its both fully open) I hope that didnt throw you off.

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