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Thread: Disolved Air Causing Dry Pump???

  1. Back To Top    #1

    Join Date
    May 2015
    Location
    Kennesaw, GA
    Posts
    28

    Disolved Air Causing Dry Pump???

    My pump and filter are about 20 ft and slightly down-hill from my in-ground pool. I have a new SWG and Pentair single speed pump. The plumbing includes a skimmer and vacuum line, and a single return. The water level in the pool is approximately 24 inches higher than the pump. If I don't shut of the valves to the two vacuum lines, and remove the pump's basket cap, water floods into the pump - as you would expect. So one might think that as long as the pool water is adequate there should never be a reason for the pump to be dry.

    However, the pump basket is often completely dry after having been off has been off for an hour or so. The presence of the air in the pump basket is preventing pool water from entering, and the pump seems to have difficulty clearing the air out of the line. When I see this situation I will normally shut off the pump and briefly loosen the pump's cap which allow the gravity-fed pool water to rapidly fill the basket, and I then re-seal the cap and start the pump.

    There is no evidence of any water leaking, and since the pool is above the pump, it would seem that if there were any kind of leak in the vicinity of the pump or filter, that gravity would keep the pump basket from becoming drained.

    MY CONCULSION: I am speculating that when the pump is off, dissolved air & gases are collecting and creating enough pressure to force the water out of the pump basket. I am also speculating that if I allow the pump to continue running for a minute or so the pump will be able to clear the line, but I am a bit concerned about running the pump when it is dry.

    Anyone have experience with this type of a phenomena/symptoms when the pump is below the pool level??
    Leo In Kennesaw, GA
    Older 40x20 rectangular pool
    38,000 gallons
    Vinyl In-ground - Buster Crabbe
    Pentair Chlorinator - Salt - SWG

  2. Back To Top    #2

    Re: Disolved Air Causing Dry Pump???

    It's not dissolved gasses. I suspect that you have a suction side air leak, which is filling the filter with air. Then when the pump shuts off, compressed air pushes water out of the pump.

    What specific pump do you have?
    Do you get air out of the returns?
    Try opening the filter air relief a few times to see if there is always air in the filter.
    Is any of the suction plumbing higher than the pump intake?

  3. Back To Top    #3

    Join Date
    May 2015
    Location
    Kennesaw, GA
    Posts
    28

    Re: Disolved Air Causing Dry Pump???

    I think you are right on. Filter pressure was the problem. Repeatedly created the problem this AM. The pressure in the filter was immediately blowing air back into the pump. Ran the backwash - which apparently took nearly a minute to clear out the air in the filter. Problem seemed to be solved. I believe this is a Hayward sand filter and a single speed Pentair 1 hp pump (1 year old). Not sure which model.
    Leo In Kennesaw, GA
    Older 40x20 rectangular pool
    38,000 gallons
    Vinyl In-ground - Buster Crabbe
    Pentair Chlorinator - Salt - SWG

  4. Back To Top    #4

    Join Date
    May 2015
    Location
    Kennesaw, GA
    Posts
    28

    Re: Disolved Air Causing Dry Pump???

    I think you are right on. Filter pressure was the problem. Repeatedly created the problem this AM. The pressure in the filter was immediately blowing air back into the pump. Ran the backwash - which apparently took nearly a minute to clear out the air in the filter. Problem seemed to be solved. I believe this is a Hayward sand filter and a single speed Pentair 1 hp pump (1 year old).

    Checked the models of pump and filter
    Pump - Pentair SF-N1-1A/340038
    Filter - Pentair/Tagelus

    Re your question about the plumbing - yes, all the suction/vacuum lines are above the pump.
    Leo In Kennesaw, GA
    Older 40x20 rectangular pool
    38,000 gallons
    Vinyl In-ground - Buster Crabbe
    Pentair Chlorinator - Salt - SWG

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