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Thread: Low Filter Pressure - Next Logical Step?

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    Low Filter Pressure - Next Logical Step?

    Hello,

    My system is running at 7-8 psi this year which is down for the previous season of 10-12+psi. I have cleaned all the strainers, ran the system without the filter cartridges and have disassembled the pump impellor for cleaning and inspection (nothing clogged). Visually, the flow rate is lower than the previous season which made me begin this investigation.

    The pool is a typical pool with a shallow and deep return jet, deep-end bottom suction and skimmer.

    What is the next logical step for troubleshooting this problem? Plumbing inspection? Motor tuneup/overhaul? I am uncertain of the age of the pump.

    Thanks for all the help!
    Carl
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    mas985's Avatar
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    Re: Low Filter Pressure - Next Logical Step?

    Lower than normal pressure, assuming the gauge is working properly, means there is probably a blockage or restriction on the suction side of the pump.
    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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    Mod Squad Bama Rambler's Avatar
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    Re: Low Filter Pressure - Next Logical Step?

    Welcome to TFP.

    Are there any air bubbles in the pump basket?
    Did the pressure change when you ran without the cartridges?
    Did the flow improve when you ran without the cartridges?
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Low Filter Pressure - Next Logical Step?

    The gauge is working properly, it zeros when the filter housing is vented. I have valves inline on both the skimmer and deep-end suction, will isolating the deep end and skimmer alternately show me where the blockage is or is a different inspection process needed? I have the ability to purge both return lines via an air compressor. Could that dislodge any blockage allowing it to pass through the system?
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Re: Low Filter Pressure - Next Logical Step?

    Are there any air bubbles in the pump basket?
    Did the pressure change when you ran without the cartridges?
    Did the flow improve when you ran without the cartridges?
    ??
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low Filter Pressure - Next Logical Step?

    There is a small amount of air in the basket as seen through the clear top. As a side note, I seem to be having to vent the air from my filter housing more often than last year. Sorry if this is a key piece, I was trying to handle one problem at a time.

    The pressure and flow did not change when run without the cartridges. When the pump was taken apart for inspection and put back together the pressure increased 1-2 psi from 6psi to the 7-8psi.
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Mod Squad Bama Rambler's Avatar
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    Re: Low Filter Pressure - Next Logical Step?

    The fact that you're having to vent air regularly from the system says there's an suction side air leak, and since the pump will pump water a lot better than it will pump air it makes sense that the pressure would be lower due to the entrained air. I would find and fix that suction leak first and see if the pressure comes back up.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Low Filter Pressure - Next Logical Step?

    I was able to go home during lunch and try a few different things. When I close the skimmer return line, the pump basket is bubble free and runs great albeit at a lower pressure (4-6 psi). When the deep-end return is closed, the pump basket becomes a roiling mess and runs at about 4 psi. This must be a air leak on the skimmer suction side. I have just one connection (black hose to hose bard with two clamps) above ground, the rest of the line is buried to the skimmer.

    Are there any tips for replacing suction lines on your pool? Is it something best left for a pool professional? I'm handy and don't mind the work. Are there any surprises I should plan for?
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    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Mod Squad Bama Rambler's Avatar
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    Re: Low Filter Pressure - Next Logical Step?

    Whoa there! Before you go to digging up lines, lets make sure your problem isn't somewhere else.

    Since it only happens with the skimmer, check the skimmer and make sure it isn't creating a vortex sucking in air. Check the weir and make sure it's working freely and correctly. Then run water over the valve to make sure it isn't sucking in air around the seals and/or stem.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Low Filter Pressure - Next Logical Step?

    The skimmer isn't creating a vortex and the weir appears to be operating normally.
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Re: Low Filter Pressure - Next Logical Step?

    I'll try the garden hose leak detection test when I am home this afternoon.
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Re: Low Filter Pressure - Next Logical Step?

    Check those black pipe hose clamps....those are terrible connections for a swimming pool.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low Filter Pressure - Next Logical Step?

    After some tinkering, tightening and a lot of water from a hose, the skimmer return line, at the hose clamp connection was leaking. I found that by dialing back the suction force on that line from full open to about a third stops the ingress of air into the filter, has my pressure at ~10psi while maintaining a good turnover rate at the skimmer.


    Should I expect the skimmer suction line to operate at full open? I tried to take the valve off the line to replace the hose clamp but didn't have any luck so I came to the conclusion that I did.
    20k gal., IG vinyl, Hayward C4025 425 ft2 150 gpm cartridge filter, 3/4 hp GE C1099 two-speed Pool Pump Motor

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    Mod Squad Bama Rambler's Avatar
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    Re: Low Filter Pressure - Next Logical Step?

    It should hold at full suction, BUT there's what's supposed to be and what's real world. If you have to dial it back then that's what you have to do. Put it in your list of things to fix down the road.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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