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Thread: Main drain - what is this?

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    Main drain - what is this?

    I closed my pool today. In doing so, I blew the main drain line out using a compressor. This usually causes the main drain cover to come off because it is not physically fastened down.

    When I looked into the main drain, I saw a piece of plastic pipe sticking into the main drain cavity from where the main drain connects to the pipe under the pool floor.

    I swam in to take a look. I could not remove the plastic pipe but it did slide back easily into the main drain pipe. The pipe was very thin and I could squeeze it with my fingers. Also, the piece of pipe that was visible had perforations in it.

    I'm thinking that the piece of pipe is not part of the actual plumbing because it was so thin. Also the spot where the main drain connects to the drain pipe appeared to be in tact.

    What was it?
    15,000 gallon unpainted plaster. Sand filter. Polaris 380.

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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Main drain - what is this?

    I am guessing but it could be the hydrostatic valve. But you shouldn't pull out the perforated pipe. That could mean the pool is leaking now. There should be a cap/float that seals to prevent water from flowing out but allows water to flow in from outside the pool shell.

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    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: Main drain - what is this?

    The main drain does not have a hydrostatic valve. The pool has 2 hydrostatic plugs which look like this -

    The perforated pipe was clearly coming out of the suction line that connects to the side of the main drain.
    15,000 gallon unpainted plaster. Sand filter. Polaris 380.

  4. Back To Top    #4

    Re: Main drain - what is this?

    Below the bottom of the main drain, there is usually a well point that connects to the bottom threaded hole from the bottom. The well point is perforated. A hydrostat is usually threaded into the same hole from the top. However, what you're describing does not seem to be something that is working as designed.

    Note: The main drain cover should always be properly secured for safety. If it ever comes off, it should be replaced with the most current approved drain cover.
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