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Thread: Lots of air bubbles from main drain, but none from skimmers

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    Lots of air bubbles from main drain, but none from skimmers

    We have a 30,000 gal in ground pool with a 1 hp hayward super pump and a sand filter.

    Drawing only from the 2 skimmers we get no air visible in the pump housing during operation, but when we open the main drain inlet to the pump, we get a flood of air bubbles - really a torrent.

    1. I know it seems obvious that there may be a break or a crack in the main drain line between the bottom of the pool and that diverter valve just before the pump intake, but is there any other possible explanation? There are no known water leaks or unexplained water loss.

    2. If you can keep the pool clean just drawing from the skimmer baskets, do you really need to open the main drain during normal operation?

    Thanks for any expert tips!

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    Mod Squad Bama Rambler's Avatar
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    Re: Lots of air bubbles from main drain, but none from skimmers

    There's not many other possibilities than a leak. Since you say that there's no water leaking I'd start looking at the piping above the water line. Maybe just under the ground or even right at the valve.

    There are a lot of pools that have had the main drain blocked off completely because of a leak, so in reality you can get by without it.
    Dave J. TFP Moderator
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    frustratedpoolmom's Avatar
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    Re: Lots of air bubbles from main drain, but none from skimmers

    If you can't locate the source - angling your returns if possible so some go towards the bottom to improve circulation should help if you don't use the bottom drain.

    Any damp or wet ground visible?
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    Re: Lots of air bubbles from main drain, but none from skimmers

    Welcome to the forum.

    Check the above ground portion of the line first....especially the diverter valve for cracks, etc. That's the most likely.

    If your pool has a deep end, I would really try to bring the main drain into play. If not, you will probably be fine without it.

    Did you try it just one time or does it do it always. If there is any air in that line at all, it will take a while for it to purge.
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    Mod Squad JohnT's Avatar
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    Re: Lots of air bubbles from main drain, but none from skimmers

    Welcome to TFP.

    Are you saying that with the drain valve open in addition to the skimmers that you get bubbles?

    If that is the case, I'd check the valve that controls the drain before going too far looking for a problem.

    Some bubbles at first may be normal if the water in the line has dropped to the pool level, leaving air in the line up to the pump.
    TFP Moderator
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    Re: Lots of air bubbles from main drain, but none from skimmers

    Yes, you get tons of air bubbles when you open the main drain valve, while at the same time drawing from the skimmers. You also get a very low flow when pulling only from the main drain, and I'm not sure it would even prime this way. I first assumed this was due to the depth we are pulling from - however with a full pool, one would think that the static pressure of a full 6' pool would be enough to push water in the main drain right up to the top of the pool level. If so, it should not be hard to pull. That then takes me back to suspecting a line or fitting break, again in the main drain line. But again with no known water leaks that doesn't add up either. So it's perplexing.

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    Re: Lots of air bubbles from main drain, but none from skimmers

    I suggest you put a wet rag or the stream for the garden hose on the any above ground sections of the pipe in question. With any luck, you’ll find a spot that stops the bubbles and you’ll be able to keep your main drain with spending much cash. It sounds like you leak is above the water level.
    20,000 Gallon kidney sort of a sand filtered gunite in ground pool w/ hot tub.

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    Re: Lots of air bubbles from main drain, but none from skimmers

    Welcome to TFP!!

    Just to summarize the advice so far -- check the connections above pool water level on the MD line, between the pool and the valve. Use the hose or wet rag to isolate the source (I've also heard that shaving cream can be used to identify where the leak is). I wouldn't be surprised if you found a bad o-ring on the valve for the MD line
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    Re: Lots of air bubbles from main drain, but none from skimmers

    Quote Originally Posted by et
    Yes, you get tons of air bubbles when you open the main drain valve, while at the same time drawing from the skimmers. You also get a very low flow when pulling only from the main drain, and I'm not sure it would even prime this way. I first assumed this was due to the depth we are pulling from - however with a full pool, one would think that the static pressure of a full 6' pool would be enough to push water in the main drain right up to the top of the pool level. If so, it should not be hard to pull. That then takes me back to suspecting a line or fitting break, again in the main drain line. But again with no known water leaks that doesn't add up either. So it's perplexing.
    There is no static head difference between a skimmer and a main drain as the water level is the same for both. Also, it doesn't matter where you pull the water from, the static head is the same.

    However, it does sound like you might have a leak in the the main drain suction line and it doesn't mean that you would necessarily have a water leak. Air and water have much different density so depending what the leak might be, it could very well leak air with the pump on but not leak water with the pump off. If shuting off the main drain eliminates the air, then the air is comming in through that line.
    Mark
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