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Thread: Main drains - How do they work?

  1. #1
    Senior Member ktdave's Avatar
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    Main drains - How do they work?

    In my pool, I have 2 skimmers, one of which (nearest to the pump) the dual main drain is connected to. In the bottom of this skimmer there are 2 holes, one with suction going to the pump, the other (no detectable pressure/suction) coming from the drain. I just don't see how any circulation is being created in the drain without it being somewhat of a closed system. Is this a "normal" configuration?

    Thanks for any insight.
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  2. #2
    Administrator JasonLion's Avatar
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    There are a couple of different ways that main drains get plumbed. That is the slightly cheaper and less desirable way. The idea behind that setup is that if the skimmer basket gets blocked with leaves the pump will draw from the main drain. Many of the two hole skimmers also have an optional float valve that fits between the pipes on the bottom and the basket that allows the pump to draw from the main drain when the water level goes below the skimmer.
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  3. #3
    Senior Member ktdave's Avatar
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    Thanks Jason!

    It seems like I could rig a "U" joint connecting the drain to the suction line that has a ball valve in it that could regulate the amount of flow btween skimmer and drain. I just feel that if the drain is there to be utilized, why not use it to create better circulation.
    11,000 gal. gunite w/midnight blue and white pearl PebbleTec
    Intelliflo 4x160 pump
    Intellichlor IC-20 SWG
    Pentair cartridge filter 420 sq. ft.
    Mastertemp 400K BTU heater
    Legend Platinum cleaner
    Pool School
    JasonLion's Pool Calculator
    TF Test Kits

  4. #4
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    Yes, ideally each skimmer and your main drain will be plumbed directly with home runs back to the equip pad. That way you can adjust circulation between main drain and skimmers.

    I use valves at the equipment pad to run one of my skimmers at the larger end of my pool at about 60% with the other skimmer about 40%. Meaning I direct more suction from one skimmer than the other. Further between skimmers and main drain I pull 70% from my skimmers and 30% from my main drain.

    This setup also has the benefit of changing suction to 100% from skimmers in case someone is paranoid about main drains. If I am doing heavy cleaning I can pull 100% from the main drain and turn the pump on high speed. I also have a main drain skimmer bag so I can clean it out pool side if needed.

  5. #5
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    I'm surprised, since yours is plumbed that way that you don't have a float valve, already.

    I never knew what it was called until I started hanging out here. I always called it "that plastic spaceship looking thingie with a sliding wing on the bottom that sits under the skimmer basket"

    Here's a pdf that explains how it works.

    http://db.waterwayplastics.com/Installa ... 0-0054.pdf
    Buggs

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  6. #6
    Senior Member ktdave's Avatar
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    Quote Originally Posted by Buggsw
    I'm surprised, since yours is plumbed that way that you don't have a float valve, already.
    I'm not suprised! This will be another call to my PB!

    Thanks for the info.
    11,000 gal. gunite w/midnight blue and white pearl PebbleTec
    Intelliflo 4x160 pump
    Intellichlor IC-20 SWG
    Pentair cartridge filter 420 sq. ft.
    Mastertemp 400K BTU heater
    Legend Platinum cleaner
    Pool School
    JasonLion's Pool Calculator
    TF Test Kits

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