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Thread: Low suction, High pressure

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    Low suction, High pressure

    About 3 months ago I had a new DE Filter installed. The pressure on my old filter ran at 12 psi, the new one at about 18 psi. At about the same time as the new filter install, I noticed that the suction from the skimmers is lower than it used to be.

    Here is what I've tried so far:
    1) Backwashed the filter immediately after the installer left. Pressure the same.
    2) 2 weeks ago I totally disassembled the filter and hosed off all of the grids. No holes or tears but there were masses of palm fibers tangled around everything.
    3) Reassembled the filter, loaded it with DE and now the pressure is now at 20 psi.
    4) Bought a Drain King in hopes that something was stuck in the pipes and I could flush it out, but I couldn't get it in past the T-bend
    [attachment=0:3tnab62e]pump.jpg[/attachment:3tnab62e]5) Tried to work a snake into the pipe with the same results
    6) Turned on the pump and the pump wouldn't prime for over a minute. Turned it on and off several times and then it finally primed.

    Since I'm obviously not having much luck, should I just give up and hope that everything is a figment of my imagination? Or do you think that I have some kind of issue (the pool, not me ..) here?
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    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    mas985's Avatar
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    Re: Low suction, High pressure

    Higher pressure means that the return side has more restriction than it use to. This would also reduce the suction. So if there is a blockage and it is not the filter, then it would be after the filter so you could try to put the drain king into the pipe right after the filter.

    However, the problem you are experiencing is probably the filter since you just changed it and return side blockage is fairly rare. What was the type and size of your old filter and what is the size of your new filter?
    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: Low suction, High pressure

    The old filter was a 60 sqft Pac-fab Nautilus NS filter. The new one is a 60 sqft Pentair Nautilus FNS filter.

    When you say "try to put the drain king into the pipe right after the filter", do you mean here (sorry I only have a shot of the old filter)?
    [attachment=0:1bg1vlyk]oldfilter.jpg[/attachment:1bg1vlyk]
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    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    mas985's Avatar
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    Re: Low suction, High pressure

    The pump goes to the input of the filter (the one you are pointing to) and the output of the filter is the other port. You want the output port of the filter. This returns the water to the pool and if you do have a blockage, that is where it would be.

    But again, I suspect it is probably the filter itself but you can try the drain king anyway. It could just be that the new filter is working properly while the old filter was not filtering at all which could explain the lower PSI.
    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: Low suction, High pressure

    Good point about the old filter. I found that in the year that we've lived in this house just about all of the pool equipment has had to be replaced.

    I guess I'll play with the Drain King in the output port since I already have it.
    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    Rockcrawler's Avatar
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    Re: Low suction, High pressure

    Just being nosy, I was wondering how could you have a blockage after the filter? It would have to get by the pump screen and the filter itself to become lodged in the return line. Unless part of your old filter broke and a piece of it was in there.

    Just wondering???
    13,000 IG Plaster, 2hp whisperflo pump, 48 sq in pentair DE Filter, 1 skimmer, 2 eyeball outlets, 200 sq ft solar panels on second story, Auto Pilot SWG-36, Polaris ATV Cleaner

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    Re: Low suction, High pressure

    Unless part of your old filter broke and a piece of it was in there.
    Or if some obstruction got into the line when the filters were being exchanged. That's probably not the case but that psi does seem a bit high for a filter and pump that size....not much.....12-16 would be more common, I think.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low suction, High pressure

    So when I blast things out with the Drain King, were is the water going to come out? From the returns?
    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    Rockcrawler's Avatar
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    Re: Low suction, High pressure

    yup, I really don't think you have a blockage, I think the pressure is like that because you have a new filter, I wouldn't think of comparing an old filter with a new one unless maybe they were the same model, and then your pentair filter is rated to 50PSI mine runs at 20 with my solar heater on
    13,000 IG Plaster, 2hp whisperflo pump, 48 sq in pentair DE Filter, 1 skimmer, 2 eyeball outlets, 200 sq ft solar panels on second story, Auto Pilot SWG-36, Polaris ATV Cleaner

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    Re: Low suction, High pressure

    Hopefully nothing nasty (I'm thinking partially decomposed creepy-crawlies) is going to shoot out!
    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    Re: Low suction, High pressure

    xene97,

    What HP is your pump and what is the service factor (sf)? Both of these numbers should be on the plate on the pump motor.

    Is your filter rated for 50 gpm or something else?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low suction, High pressure

    Here's the label from the pump
    [attachment=1:iz9dyqyb]pump.jpg[/attachment:iz9dyqyb]
    If I read the Model correctly, according to Google the pump is a DuraGlass II 2 HP Swimming Pool/Spa Pump

    The motor was replaced around the beginning of the year since the old one basically melted (bad electrical wiring going to all of the pool equipment). It was replaced with this:
    [attachment=0:iz9dyqyb]motor.JPG[/attachment:iz9dyqyb]
    Century Centurion
    Total HP=2.20
    SF=1.10 or 10.0 (depending on which SF you mean)

    The filter is rated at 150 GPM ("This flow rate is based of 2.5 GPM per sq. ft. of filter area" according to the filter manual).

    Hopefully this helps.
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    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    Re: Low suction, High pressure

    Thanks!. That answers why your psi is somewhat higher than a normal system.

    That is one big pump for that pool!!

    The filter is large enough to handle it (barely) but it would explain to me why your psi is running up around 18. Mas985 is the guru but, from experience, that pump and filter (plus you may have some 1.5" piping, not sure) would seem to operate normally right around 18psi give or take.

    FWIW, that pump would do better on a 50,000 gallon pool. You are probably turning your pool water in under three hours when 8-12 hours would be normal.

    I don't know how long you're running your pump but your burnin' up some electricity when it's on.

    Back to your original question, I can't answer why the old filter seemed to handle the pump power better than the new one. Do you happen to know if the old one was rated any higher than 150gpm? I know you said they were both 60 sq ft. so I doubt it.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low suction, High pressure

    Nope. Both filters were/are definitely 60 sqft units. You can actually see the old stainless steel one in the second photo above.

    As to the pump, should we downgrade and get something smaller? Or can I run it for less hours (in the height of summer, about 10 hours)? I'd love to save on the electrical bill since our last one was obscene and I know this month is going to be much, much worse.
    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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    Re: Low suction, High pressure

    Duraleigh-

    I just checked the manual for the old DE filter (Nautilus NS 60 Stainless Steel DE Filter 60 sqft) and the old one is also only rated at 120 GPM residental (based on 2.0 GPM/sqft) or 90 GPM public (based on 1.5 GPM/sqft).

    Christine
    18K (I think) gal gunite pool, Pentair FNS DE Filter, Polaris 280 cleaner, TF-100 Test Kit

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