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Thread: Blowing out skimmer and main drain

  1. Back To Top    #1
    ship of fools's Avatar
    Join Date
    Nov 2011
    Albany, NY

    Blowing out skimmer and main drain

    Hello everyone ... 2 year lurker and first time poster here.

    I bought a house with an existing pool two years and stumbled on this site and have learned enough that i believe next year i will take the plunge and become a BBB convert. I started off using Sustain and have had good results but as you all know it is a wee tad pricey

    In the meantime i have a quick question. Two years ago i paid a guy to close the pool and watched him. Last year my brother and i did it with him directing and me doing the work (he owned a pool for many years) and had no trouble.

    This year i have been planning on doing it myself... ran through several online guides etc and feel very comfortable of the steps and process to get things done.

    Of course i have an issue ...... when i am blowing out the main drain and close the valve it appears that the bubbles continue to flow out even though the valve is closed before i shut the compressor off ... it appears that air is still coming out of the skimmer when i blow it out ....... i was under the impression that once i shut the valve there would be an air lock ... but if i still see bubbles coming out wouldnt that mean water could leak back in?? Is it possible the valves are old and shot?? .. It is a 30 year old pool and i did have intermittent issues getting good suction with the vacuum this year.

    Outside of this i am very comfortable and confident doing the rest .... but these could obviously cause some major problems so i need to get some answers or call a pro.

    Thanks in advance
    21,000 gallon inground
    Haywood Sand Filter
    Vinyl Liner

  2. Back To Top    #2

    Join Date
    Jun 2007
    New Jersey

    Re: Blowing out skimmer and main drain

    I'm no expert, but I think I can respond to this. When you blow the main pipe, it is is full of air that has displaced water and is flowing up through the drain. When you close the valve, some air will continue to the surface because it is past the lowest point in the plumbing, and is free to go to the surface though the drain. This is what you see. Water then enters the plumbing to replace this air and traps the air that remains on the other side of the low point and further rises until the trapped air in the pipe is compressed to a pressure equal to that of the column of water in the pool above the level of the of the water in the drain pipe. This will still be below the frost line and will remain liquid through the winter.
    Current: 28,000G 18'x36' I/G AnthonySylvan Plaster; Waterway 60 sq.ft. DE Filter; 1.0hp x 1.65 SF Two-Speed (B2982) WhisperFlo; 2004-Present
    Previous: 40,000G 20'x40' I/G Koven unlined WWII salvage 5/8" marine steel; Lomart Stainless Sand Filter; 3/4hp Hayward SuperPump; 1946-2003 (managed by me from about 1964)
    Ancient Taylor K-2000, upgraded with Taylor CH, TA, and FAS-DPD, and TFT CYA tests.

  3. Back To Top    #3
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    SouthWest Alabama

    Re: Blowing out skimmer and main drain

    Durk did a very good job of explaining what happens. As long as the water remains below the forst line there's nothing to worry about.
    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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