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Thread: Question about main drain

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    Question about main drain

    My pool has what I'm assuming is one main drain (white plastic cover with concentric grates) in the middle of the deep end; excuse my ingnorance, but what is the purpose of this?

    Although this question popped into my head last year (1st pool season), never had a problem with the drain, so the need to have this question answered wasn't pressing; however, while brushing my pool earlier tonight, whenever I brushed near the drain and surge of water whooshed by it, a bit of debris (algae? soggy leaves? same thing?) would come out of the drain. So I guess my second question is...what the heck's happening? and how do I get it to stop?
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    Re: Question about main drain

    Are you referring to a Main Drain, or a Leaf Trapper used in a Caretaker system?

    Most pools have two main drains. There should be two valves in front of your motor, a Skimmer and Main Drain Valve. Is your Main Drain valve open? If so, it's possible that someone has plugged your main drain. Some people find leaks in their main drains & instead of repairing them correctly they just plug off the main drain with a threaded cap. This causes water to become stagnate in the bottom of the drain & since Algae likes to grow in dark places (similar to the water behind your pool light) it's one of the 1st places algae will blossom.

    If you have several 1.5" round pop up jets in the bottom of your pool, you have what is known as a Caretaker system. Each one of those jets pops up and sprays a stream of water in a sweeping motion pushing debris, dirt, sand etc towards a centrally located "leaf trapper" in the bottom of the pool It will have a flat surface with two little crescent shaped holes in the top similar to this http://www.poolsinc.com/caretaker-le...ent-parts.html If this is your case, the caretaker system not being operated will cause the same water to be stagnate and grow algae.

    To fix Main Drain issue. 1) make sure MD valve is open 2) if it is, swim to the bottom, remove the two screws on the main drain cover and see if anything is blocking the piping.

    To fix Caretaker system. Operate the jets at least 30 minutes every day or every other day to flush the piping with fresh sanitized water.

    Let me know if you need any other clarification.

    Joe
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    Re: Question about main drain

    Algae grows in the dark? Bacteria yes, but Algae?
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    Re: Question about main drain

    ^^ Thanks for the explanation, Doc; here's some more info about my pool: There is only one valve in front of my pump (!). What does this mean? Is it possible that one valve controls both skimmer and drain? doesn't sound possible to me. This would mean that any time my pump is running, water is being drawn in from both the drain and skimmer?
    Experts please chime in!

    I'm currently in the process of draining some of my pool water (see my other thread), so I have my filter valve turned to waste; will this help dislodge some of that crud stuck in the drain?
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    Re: Question about main drain

    Quote Originally Posted by saysomething
    ^^ Thanks for the explanation, Doc; here's some more info about my pool: There is only one valve in front of my pump (!). What does this mean? Is it possible that one valve controls both skimmer and drain? doesn't sound possible to me. This would mean that any time my pump is running, water is being drawn in from both the drain and skimmer?
    Experts please chime in!

    I'm currently in the process of draining some of my pool water (see my other thread), so I have my filter valve turned to waste; will this help dislodge some of that crud stuck in the drain?
    Look under your skimmer basket and see if there's two holes. If there is, there should be some sort of diverter to adjust the balance between skimmer and main drain. There are pictures in the encyclopedia in pool school. My pool was misisng the diverter; it cost about ten bucks, and I can adjust things to draw from drain or skimmer, or some combination. Finding the balance point is trial-and-error, though.
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    Re: Question about main drain

    Ditto Richard. It may be the size of an oversized hot dog bun. There should be a little T handle that moves a plate. That plate adjusts the suction between Skimmer and MD.
    "When your pool is sick, call the doctor, I make house calls"
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    JasonLion's Avatar
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    Re: Question about main drain

    It is possible for a single valve to control both the skimmer and main drain, but only if it is a three way valve (three pipes coming into the valve in total). If you have that kind of valve, the two pipes would be skimmer and main drain, and the valve will allow you to draw water from either one, or both, of those places.
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    Re: Question about main drain

    Quote Originally Posted by Richard320
    Look under your skimmer basket and see if there's two holes. If there is, there should be some sort of diverter to adjust the balance between skimmer and main drain. There are pictures in the encyclopedia in pool school. My pool was misisng the diverter; it cost about ten bucks, and I can adjust things to draw from drain or skimmer, or some combination. Finding the balance point is trial-and-error, though.
    Under my skimmer basket are two holes; one is currently plugged with a rubber stopper (same as the ones I use to plug my returns). I guess I'm missing the diverter. Do all pool stores carry these?

    Once I do have one in place, how do I know I've reached the ideal balance point?

    Also, if I were to move the stopper to cover the skimmer drain and then turn on my pump with the valve turned to waste, would this help clear up the crud I mentioned in my OP?
    24k gal (100k L) inground vinyl|Watermaid EZY SWG|Hayward 1/2 hp & sand filter

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    Re: Question about main drain

    Quote Originally Posted by JasonLion
    It is possible for a single valve to control both the skimmer and main drain, but only if it is a three way valve (three pipes coming into the valve in total). If you have that kind of valve, the two pipes would be skimmer and main drain, and the valve will allow you to draw water from either one, or both, of those places.
    I can only see one pipe before the valve; my plumbing knowledge is very limited, but I'm guessing for a 3 way valve to function properly, the pipes would have to be joined directly at the valve point not at a point before the valve (in my case, this would be underground).
    24k gal (100k L) inground vinyl|Watermaid EZY SWG|Hayward 1/2 hp & sand filter

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    Re: Question about main drain

    Right, for that kind of valve to work, the pipes join at the valve. If it isn't one of those valves, the two possibilities are that the pipes connect underground, or that the main drain pipe comes up inside the skimmer (as others have already pointed out). It could still be either of those possibilities, though coming up as the extra pipe in the skimmer seems a little more likely. The one thing to watch out for is that the extra hole in the skimmer might not be connected to anything and removing the plug might cause a leak. It is more likely that it goes to the main drain, but you never know.
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    Re: Question about main drain

    Thanks, Jason; I'm going to remove the plug and keep an eye on the water level.

    What happens if a diverter in the skimmer is not used at all or not properly adjusted? and how do I know when I've reached ideal adjustment?
    24k gal (100k L) inground vinyl|Watermaid EZY SWG|Hayward 1/2 hp & sand filter

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    Re: Question about main drain

    Quote Originally Posted by saysomething
    Thanks, Jason; I'm going to remove the plug and keep an eye on the water level.

    What happens if a diverter in the skimmer is not used at all or not properly adjusted? and how do I know when I've reached ideal adjustment?
    Basic physics. Would you find it easier to draw water from the surface level of the pool, or from eight feet down through a pipe with bends? What happens is you get nothing from the drain and everything from the skimmer.

    Adjusting the diverter is just experimentation. I set it to halfway and watched the movement in the skimmer. Then I kept moving it until it wasn't all skimmer, but it looked pretty much the same. Then I took the brush and nudged some debris at the drain, when it got pulled in, I knew I had some flow there. The best part is, my pool temperature is uniform, surface to floor, no colder bottom layer!
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Question about main drain

    Okay so the plug is removed, and the main drain seems to be pulling in a bit of water according to the debris test Richard outlined above. I think what I should have done is plugged my skimmer opening and set my filter to waste, so that none of the crud would be ejected back in to the pool. Now the pool water seems just a bit cloudier than before. Lesson learned. Next step: Shock and buy a diverter! Thanks for the help, everyone!
    24k gal (100k L) inground vinyl|Watermaid EZY SWG|Hayward 1/2 hp & sand filter

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