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Thread: How critical is a main drain?

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    How critical is a main drain?

    I have a 16'x32' hopper bottom IG vinyl liner pool. Deep end is 8'. Pool is 20+ yrs old, only has one return in the shallow end parallel to the 16' side, same side of pool as skimmer which is mid pool on the 32' side. Main drain centered in the 8' deep end.

    About a month before I planned to open this year, I noticed the pool cover seemed to be getting lower on the water surface. Sure enough, something was leaking, so I had to open early to try to get a handle on what was going on. Water level would drop below all the usual suspects like return, skimmer and cut in steps, so they weren't the source of the leak. Luckily I was able to add water and stay ahead of the leak, which settled into losing about 2" or so every day. When the water finally warmed enough to get in I spent several hours with a dive mask examining the liner and die test the main drain, as we'd had a new roof put on our house the prior fall and even though the pool was covered there were about 8 nails in the deep end. Main drain seemed ok and I couldn't find a thing in the the liner, which was frustrating. Finally I removed the grate cover of the main drain and sure enough die showed there was a small draw into the line. I plugged it last night, and didn't lose a bit of water overnight.

    At this point my realistic options as I see them are to simply keep it plugged and operate the pool with just the skimmer and one return. However my pool seems to suffer from inadequate circulation and I get dead zones around the deep end walls and algae growth in an otherwise crystal clear no CC pool, especially when the pool isn't getting used as much. I've been contemplating actually re-plumbing the main drain to be a return to increase deep end circulation, but am now wondering how long this leak has been going on and I've been chalking water loss up to evaporation, as with my skimmer closed my whisper flo has never been able to fully pull from the main drain, I get about 1/2 a pump pot of air and low flow. Maybe that's why circulation has been bad in the deep end?

    What would you do? I have talked to the people at Marlig and they seem to think their fix a leak product has a shot at sealing the main drain line. Would be cheap enough to try, but if it won't solve the circulation issue I'd be just as inclined to simply leave it plugged.

    Thoughts?

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    JasonLion's Avatar
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    Re: How critical is a main drain?

    Fix-a-leak won't work on suction lines unless you reverse the water flow to make it a pressure line temporarily.

    Having a main drain is nice, but hardly essential. Many many pools don't have main drains. With only one return you want to spend a little time getting it aimed just right, so the water circulates in oval around the pool, surface debris is carried to the skimmer, and also slightly downwards to promote mixing of deep water.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: How critical is a main drain?

    Quote Originally Posted by JasonLion
    Fix-a-leak won't work on suction lines unless you reverse the water flow to make it a pressure line temporarily.
    Yes and this could be easily done with my set up.

    Having a main drain is nice, but hardly essential. Many many pools don't have main drains. With only one return you want to spend a little time getting it aimed just right, so the water circulates in oval around the pool, surface debris is carried to the skimmer, and also slightly downwards to promote mixing of deep water.
    My pool has never had an eye, just a 1.5" threaded opening which is about 18" down from the top of the wall and aimed straight at the opposite wall. Do you think an eye would help circulation wise?

    After I typed the OP I'm leaning towards trying the fix a leak just to satisfy my curiosity as to why the pump can't full pull from the main drain.

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    JasonLion's Avatar
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    May 2007
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    Re: How critical is a main drain?

    Yes, a properly aimed eyeball fitting would make a huge difference.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: How critical is a main drain?

    Thanks.

    I'm looking at this one-

    http://eco-blu-pool-components-llc.webstorepowered.com/

    In my rectangular pool, would you still direct the flow parallel to the wall but downwards? Or more angled towards the deep end? Right now it's pointed right at the wall and making the turn even just coming out of the 1.5" opening.

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