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Thread: Pressure drop on sand filter

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    ned8377's Avatar
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    Pressure drop on sand filter

    Anyone know what would cause the pressure to drop about 4-5 psi on the sand filter for no apparent reason? It has not been back washed etc. Could it have developed a channel through the sand? I've seen it do this once before and then it would go back to normal pressure after a while. Thanks.
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Mod Squad YippeeSkippy's Avatar
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    Re: Pressure drop on sand filter

    Did you remove a cleaner or turn any of the valves? You didn't backwash before the drop I take it? If you're concerned about sand channeling you could always pop it open and look. Perhaps give it a little clean while in there..... Just a suggestion
    My Amazon Smile for November12K Fiberglass IG, Infinity 4000 automatic cover, SWCG, Hayward Sand Filter, Hayward 1.5 Pump, Doheny Discovery Robot, Savi Melody LED pool lights, outdoor speakers and other assorted doo-dads. Sundance Altamar Hot Tub.
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    Re: Pressure drop on sand filter

    No didn't change anything. Actually, the only other time I noticed it was after a back wash and then a couple of hours later it was back to normal. This time, I have not back washed. Went outside to check things and noticed pressure had dropped. Thanks!
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: Pressure drop on sand filter

    PSI drops because of decreased flow on the suction side. Of course, a faulty gauge can be an issue, but typically, you will find some obstruction somewhere between the impeller on the pump to the skimmer(s).

    Most folks assume the worst and think it is the underground pipe.........while it can be, it almost never is.

    What have you inspected so far on the suction side of your system.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Pressure drop on sand filter

    Ok, I went out and emptied all the skimmer baskets and pump strainer. Not sure how to check the impeller. Ended up with same pressure. Then I backwashed as usual and it went back to same pressure. You are right that an obstruction could decrease pressure since turning off the main drain or skimmer will do the same but they are all on. I have a return jet in the shallow end that blows close to the top of the water so I can visually see the circulation and it is better than it has been in the past. All the skimmers seem to have good circulation. When turning off the main drain pressure drops further as it should.

    I've always had a problem with the pressure running too high in my opinion at about 26 psi after a backwash. I would wait for it to get up to no more than 35 psi before backwashing again and it would always go down to about 26-27 psi. Now it is running at 20 psi which is more in the range of where it should be.

    If the flow, from the return jet, in the shallow end is, visually, at least or greater than it usually is and all the skimmers seem to be sucking normally, am I right to assume there is probably no obstruction?

    Thanks for your help!
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: Pressure drop on sand filter

    Now it is running at 20 psi which is more in the range of where it should be.
    Why? What is different from when it was at 26 psi?

    Decreased pressure (that's you) and an increase in flow (that's apparently you, too) indicate you have removed a restriction from the pressure side of your system.

    When did that drop in psi occur?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Pressure drop on sand filter

    Maybe the gauge is defective. We had weeks of rain starting around Sept 24 here in NC. Ever since then there have been droplets of water inside the gauge that won't go away. Went out and started the pump this morning and now pressure has moved from 20 psi to about 24 psi. You can see where I used to have it set at 26 to about 35.

    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: Pressure drop on sand filter

    Moisture inside the gauge, is usually a sign of a gauge in need of replacement. TFTestkits.net sells a real good one that is glycerin filled. Lots of folks here have one and really like it.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Pressure drop on sand filter

    If this was my filter I would change the gauge for one that I could read.

    I have installed one of these on my sandfilter, it's a high quality gauge at a reasonable price.

    http://tftestkits.net/Flow-Meters-and-PSI-Gauges-c12/

    HTH,
    Dom
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    Re: Pressure drop on sand filter

    seconded on the tftestkits glycerin guage...it's a very good price...I just got one a month ago...very happy with it.
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
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    EVChargeGuy's Avatar
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    Re: Pressure drop on sand filter

    I third the Glycerin filled gauge, got one this year from TFTestkits and there is no guessing as to the real pressure
    IG Tear Drop, Dark Gray Gunite , 27,000 gallons -Age 50+-years, very old Hayward Split Egg Sand Filter with side mount Multi-port- Hayward SP2600VSP Pump- Hayward chlorine feed (not used since finding TFP) - Laars 315K BTU Oil heater- LoopLoc Safety cover- AquaBot RAPIDS 4WD- TF-100 Test Kit w/ Speedstir- 390 Gal Hot Springs Spa Envoy installed May 2017

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    Re: Pressure drop on sand filter

    What does the glycerin do? Does it keep the water out? Also, would I not need a gauge that goes over 30 psi? I guess my gauge has always been registering too high. Thanks for the advice.
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

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    Re: Pressure drop on sand filter

    I think it might have something to do with withstanding lower cold temperatures as well as smoothing out the needle when it moves, but one thing I did not like about it then
    changed my mind is the bubble showing at the top of the rear mount one.

    Then I realized the left and right edges of the bubble is the exact area where markings would be for "time to back wash"
    and "just backwashed" areas of the gauge...at least on my pump/filter setup it is.

    Most residential pools should not need a gauge going beyond 30.
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
    (1.5 HP motor) Raypak PR266AEN (266k btu) gas heater. TF-100 Test Kit.
    Dolphin E10 Cleaning Robot.

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    Re: Pressure drop on sand filter

    The glycerin protects from freezing down to around 4 degrees F. (I think). The air bubble in the gauge is mandatory.....pressure equalizer.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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