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Thread: Main Drain not working?

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    buddywiser's Avatar
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    Main Drain not working?

    I was trying to drain some water out of my pool (High CYA). When I got below the skimmers, I shut both of them off at the pump, but no water would come through. After some reading last night, I'm wondering if this is the problem. Underneath the skimmer basket, the hole closest to the pool is plugged up. This one runs to the main drain right? Does is need to be unplugged? It looks to be a plug with a big square cutout in it.
    24000 Gal, 18x36 Vinyl
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    JasonLion's Avatar
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    There are many different ways to plumb a main drain. It might not be connected to the skimmer. Are you sure there isn't a pipe for the main drain at the equipment pad? Also, if it is connected to a skimmer, it would only be connected to one of the skimmers, not both.

    It doesn't make sense to me to have a main drain plumbed to the skimmer and have the hole plugged, though obviously it could happen. It seems far more likely that they simply used a double hole skimmer and the plugged hole isn't connected to anything.
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    buddywiser's Avatar
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    Yes, there is a pipe at the pad for the MD, and 2 more for both skimmers. I saw some illustrations that showed the MD going to the pump AND to a skimmer (the Equalizer for stopping air from going into the skimmer at low water levels). I just figured that all were like this. You're probably right, mine may not be. I was assuming that they were there for winterizing and I should have taken them out. Maybe my MD is just clogged up.
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    JasonLion's Avatar
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    If you take the pump strainer basket out you can often fit a garden hose with a drain king attached into the inlet pipe. With the skimmer valves turned off you can then try flushing the main drain pipe out back towards the pool. That will tend to make a little bit of a mess in the pool, but usually gets the pipe clear with minimal work.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    buddywiser's Avatar
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    Thanks a bunch! I'm going to go look around for one of these. That looks like a handy product to have.
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    buddywiser's Avatar
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    Okay, time to revisit this problem since it's getting near closing time. My main drain is still not working. I took off the main drain cover, put in the Drain King on the pool end, and water comes through to the pump. So it doesn't look like it's clogged. But I can't get the pump to suck any water from the MD. I'm pretty sure the skimmers are shutting off okay. There's just no water coming into the pump when I turn off the 2 skimmers. Any other ideas? Jason, you mentioned a possible leak. I've gone the whole season without a MD, so I'm not too worried. I can probably do without it, but it would still be nice to get it working.

    By the way, I just became a Lifetime Supporter cause this is the most awesome site!
    24000 Gal, 18x36 Vinyl
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  7. Back To Top    #7
    JasonLion's Avatar
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    When you say "There's just no water coming into the pump", what exactly happens?

    Some people need to prime the main drain by getting the pump running with just the skimmer(s) and then openning the main drain valve very slowly. That will allow the pump to clear any air in the main drain line without losing prime. Then the skimmer valve(s) can be closed and you should be drawing from the main drain only. This can be verified by checking that no water is being drawn into the skimmers and water is still coming out the returns. Also, watch the pressure gauge when turning off the skimmer to go to the main drain only, it should go up just a little bit. If it goes up dramatically the pipe is too clogged (could be just a partial clog).

    If the pump loses prime (pump strainer chamber fills with air) when switched to main drain only then you are either failing to prime the main drain or there is probably a leak letting quite a bit of air into the main drain pipe, probably at or near the equipment pad.
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    buddywiser's Avatar
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    When I open the skimmers only, the pressure is 13. I tried opening the Main Drain slowly (many times) but that did nothing. Opening and closing the MD has no effect on the pressure. The needle didn't move even the slightest bit. If there's a leak in the MD line, shouldn't opening and closing the valve have some effect on the pressure?

    Anyway, after I have all 3 open, when I slowly close 1 of the skimmer lines, the pressure drops to about 9 and a little bit of air gets into the pump. When I have both of the skimmers closed, more air gets into the pump and the pressure drops to 0.

    Just one more questions. My pump is 10 years old. And I had an electrician tell me that the motor is losing some power before. Does it take more power to pull from the MD than the skimmers because of the depth?

    Anyway, I thought a pic of my setup might help a little too. The MD is the upper rightmost line and the other 2 are the skimmers.
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    Hi, Buddy,

    If your pressure drops to zero when the skimmers are both closed, the main drain is not functioning at all. There is a blockage somewhere between the drain and the pump.

    My guess is a previous owner closed it off....is that possible or are you the only owner. The next most likely is that something got into the drain when the screen was off.....blocking the water from entering. (tennis ball)

    I can't picture the test you did with the drain king to insure you were getting flow from the drain.....something doesn't seem valid in that test because a pressure of zero means no flow....none. Describe how you did that again and I'll see if I can understand.

    Lastly, the obstruction is usually close to one end or the other. The valve that shuts off the drain could even be plugged but not likely. My guess is an obstruction near the drain....either on purpose or accidental.

    As an aside, the depth of the drain is unrelated to the pumps ability to draw water from it.
    Dave S. - Forum owner
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    buddywiser's Avatar
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    Dave,

    I dove down to the bottom of the pool and took the cover off of the main drain. I took a hose down and put the Drain King into the main drain line at the bottom of the pool. I then took the lid off of the pump. I then turned the water on and it started coming into the pump. The water level was low in the pump, so I could see the water coming in. The skimmer lines were closed and only the MD line was open. I dove in to make sure the Drain King was working. Everything was snug down there. That is what I can't figure out. I can run water from the MD to the pump with the Drain King, but I can't get the pump to draw it out on its own.

    It's a 10-year old pool, but this is my first year at this house. I was also thinking that the valve might not be opening or closing.
    24000 Gal, 18x36 Vinyl
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    Hi, Buddy,

    Man, that's puzzling. I'm curious about another easy experiment. Prime your system and get it up and running with little, if any air in the pump basket, then shut the pump off....The water should stay in the pump basket. Then close both valves to the skimmer but leave the MD valve open. Now open the top of the pump basket. Depending on how high your water pump is above the pool, the water should rather quickly pass thru the pump basket and back into the pool thru the MD. Your filter will gurgle quite a bit as the water drains from the filter thru the pump back into the pool.

    If the water recedes slowly out of the pump basket (or conceivably even overflows), then that confirms there's a blockage somewhere between the MD ball valve and the MD and confirms why you're getting 0 psi when you isolate the MD.

    Post the results of that back and we'll all help get it figured out.
    Dave S. - Forum owner
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    I'd bet you're pulling air somewhere on that main drain line, suspect being the valve perhaps. That kind often doesn't seal properly on the suction side IME.

    That aside, try priming your pump with the skimmers off and try to get it running that way with just the main drain. I know on my system for start up the pump is primed and only once it's running smooth with just the main drain then the skimmer valve is opened.

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    Okay, I tried a few things. I couldn't get it to prime with just the MD open. I've tried that numerous times over the last few weeks to no avail.

    Next test: Turned off pump - no air in pump. Closed skimmers - still no air. When I opened the pump, the water went down slowly. Not too slowly though. I would say it took about 5 seconds to go 2 or 3 inches. But If I had to guess I would say that the water went the way of the filter, not back into the MD line. Because when it went below the flapper, it kept going down at the same pace.

    So let's assume that it's getting air right at the MD valve. Wouldn't that have some kind of effect on the skimmers too? With both of the skimmers open, there is no air in the pump. Or could it just be pulling enough water from the skimmers to take the air out of play?
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    Buddy, I think that kinguni may have hit on the problem. I would take a look in that valve, as there is a union before the pump and all 3 valves have unions - it shouldn't be too hard to get in there. Once it's apart, if everything looks normal (be sure to check the o-rings that seal it, they may be rubber or plastic - if one on the MD valve is broken, pinched or missing, that could be the problem) - try the drain king from the topside, there's still a chance that there is an obstruction and reversing the flow through the line might clear it. (to save you from asking, a partial obstruction will allow water forced through it to enter the pump but when trying to suck through it, the water will cavitate, perhaps enough to kill the prime.)

    If you want to play with the valves a little before disconnecting the unions, get the system running off of the skimmers with the MD open. Now 'slam' the "NS" valve closed - if the pump starts collecting bubbles give a good listen around the MD valve, you should be able to hear the leak if it's above ground. If just closing the "NS" valve isn't enough to get the air to draw, slowly close the "FS" valve until you get the air and start listening for the leak. Given that running just the MD kills the prime quickly, you should still be able to hear or feel (wrap your hand around the pipe just below the 90 elbow) air passing through the pipe, if the source is below ground. Speaking of which, are you loosing water?

    This is the best I can come up with at the moment, hope it's somewhat helpful

    BTW- Happy Labor Day everyone
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

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    buddywiser's Avatar
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    Waste,

    You know, over the last few weeks I have felt that maybe I was losing more water than I should have. I actually found myself wondering if the heat pump that we put in this year may have had something to do with that. Since it gets a littler colder at night now (North Central WV), the heat pump runs more than it did. I was wondering if there was normal water loss during the heating process. And we still have about 5 kids a day swimming for 5 hours, so a lot of water gets splashed out of the pool. But I still think it's been more than usual.

    So last night I closed the MD at the pump, and plugged the MD at the bottom of the pool. I figure if there's a noticeable difference in water loss (to the good side) in the next few days, then that could be the problem. I'll post back with what I find out.
    24000 Gal, 18x36 Vinyl
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    Dude, you're doing it just the way the pros would Without pressure testing the line, you've isolated it and are checking for water loss. You seem to have a knack for this!

    I used to live in Wheeling, how're things in West BY GOD Virginia? :P How 'bout them 'Eers

    Please keep us posted with what you find! we're all rooting for you !
    Luv& Luk
    -Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

    POOL SCHOOL, TF Testkits, Jason's Pool Calculator, CYA vs. cl chart, (Just a few DARNED handy links!)

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    buddywiser's Avatar
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    Well, I think I may have the leak isolated. And it's not in the MD! Duraleigh mentioned ball valves sometimes not working correctly and letting water get through. So I just started playing around at the pump. When I unscrewed the pipe that leads to waste (No offense, waste ) I found that water was leaking out of the filter to the sewer when it was supposed to be shut off. Not much, but I think I may have found the culprit. Now if this is the true, then it probably explains why my CYA has gone from 130 to around 50 over the last 6 weeks. And the high CYA is how I found out that the MD wasn't working in the first place. So my next step is to take out the leak (new ball valve?) and then it's back to the MD.

    Waste, I'm in Morgantown and it's pretty crazy here, as you can imagine
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  18. Back To Top    #18
    buddywiser's Avatar
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    Re: Main Drain not working?

    I'm revisiting this issue. Every now and then I take some time to see if I can solve this problem, but haven't done so yet. My pool is in great shape with just my 2 skimmers working, but this still eats at me. To recap, my pump will NOT pull any water from the Main Drain.

    - If I put a Drain King at the pump, water comes through the MD.
    - If I put a Drain King through the MD, water comes out through the pump.

    I have tried to snake it out with no luck.

    The reason I'm posting at this time is because of what I came across today. There's a square "skimmer cover" that the previous owners never were able to lift up. It is located in the corner of the pool at the deep end. I messed around with it and got the cover off and under it is a PVC pipe that looks as though it heads straight to the MD. The pipe is open, sort of like it could drain standing water from the concrete through the little hole of the skimmer plate that sits above it.. There are 2 holes in the MD. The one that runs to the pump and the one on the bottom of the MD. The one on the bottom seems to be plugged up with gravel. I'm just guessing that this hole is where the PVC pipe heads to. I know that the MDs are sometimes connected to the skimmers, but I don't think mine is.

    If I'm correct and this PVC pipe leads to the bottom of the MD, could this be why I can't pull water from the MD. Maybe it's letting in air? Has anybody seen anything like this before?
    24000 Gal, 18x36 Vinyl
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  19. Back To Top    #19

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    Re: Main Drain not working?

    buddywiser,

    Can you post pictures of your skimmer?

    I'm not sure if I have the same setup that you do, but I have 2 pipes in my skimmer. One pipe goes to the filter pump and the other pipe goes to the main drain. There is a "float valve assembly" on mine which has a "flapper" that lets you adjust the percentage of skimmer versus main drain. Except that my "float valve assembly" was missing the "flapper" and I didn't even realize until I bought a new "float valve assembly" at the local pool store.

    Without the "flapper" 100% of the suction comes from the skimmer and 0% comes form the main drain. I went around 2 years from when we bought the house until I discovered this little fact. So I never had any flow through my main drain for this 2 year period.

    Titanium
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  20. Back To Top    #20

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    Re: Main Drain not working?

    Buddywiser: Is it possible that this extra skimmer plate with the pipe in it is an air inlet for winter closing? I have that setup and you have to plug the hole (mine has a threaded plug) in order to draw a prime when opening the pool.
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