Every Pool Owner's Worst Nightmare

[Vinyl_Guy]

I don't know anything about main drains, because my IG pool doesn't have one, so hopefully somebody else will come along to give you useful information about that.

Yikes what a mess. Seen a few trees, tree branches (actually big limbs) too take out liners.

1. Should I have whoever replaces the liner see what's what with that main drain?

If you've been given any advice or told you need it for circulation, it's really ideal to have it looked at now (see next quote).The previous owner may have plugged it in an attempt to stop a leak or for who knows what reasons. It could be just fine, and only needs to be unplugged to reactivate it. So for that reason I'd have it checked out. You could gain the use of it for only the additional cost (if any) of a pressure test. A pressure test is a must, to make absolutely sure there's nothing wrong with it. If something is wrong physically with the "pot" (the body under the drain cover), it's the only time to fix it. I normally didn't charge to pressure test a main drain when doing a liner replacement. But that was me.

Might I get a lot more water circulation with it open?

Well this is a question for the ages. One of the very smart poster here might be able to explain it or answer it. Think of it this way. If your pump is fully primed, would an additional line add more volume to the flow? Or would it just reduce the suction on the existing lines already in use (skimmers and "sidewall" suction), thus spreading it out amongst more sources of suction? A lot of things can influence whether volume changes. Power of your pump. How many returns you have, because getting the water back in the pool is also related to how much a pump will "draw". Bottom line when your talking circulation, we're looking for the time it takes to draw the entire volume of the pool out, into the filter, and back into the pool (turn over). Or GPM gallons per minute, in relation to your pool size , . The more GPM effects particulate matter, more GPM means more particulate matter being skimmed, sucked and filtered. More GPM also means your chlorine , if put it in the skimmer, or in an auto-feeder will output more, but since most auto-feeders have a "choke/dial" this isn't a factor. The most that would happen is you'd have to actually turn your feeder back a notch. Unless your auto-feeder while fully "open" wasn't able to inject enough chlorine into the pool, more volume will help that. But that's rarely the case. How more volume affects "floating" type chlornation or manually adding chlorine, is a question for the chemical experts on this forum. I'm a nuts and bolts guy .

Would any debris that gets sucked into it then land in the sand filter or the secondary trap at the pump?

Yes, the same as any other point of suction (skimmer or "sidewall" suction). If your finding yourself vacuuming the "hopper" (bottom square area) of the pool, it might help. Anything that finds it way down there and then near the drain will get sucked into your pump basket, and anything too small for the pump basket will go into the filter, same as the skimmers. With a proper lid on the drain, the opening for debris is actually smaller then the plumbing in a skimmer. Unless you've got additional devices on in your skimmer for such things. So the "Barbie Doll" in the suction line scenario is less likely with a main drain. Again that's with a proper drain cover, which leads to your next question.

And, what about safety, that concerns me after hearing stories of children being eviscerated at commercial pools by the main drain. That said, I wonder where the leakage problem was?

Saftely wise if it's a standard vinyl liner main drain "pot". You need (probably by law in your state), an anti-vortex cover. Do not under any circumstances (if the line is reactivated) have a cover that looks like a "grate" installed. The cover should have no openings on top,it be domed and only have openings around its edges.

Picture of typical anti-vortex cover (it is "domed").

Absolutely do not have a main drain cover that resembles anything like this, with a flat and slotted surface!!!!!!

The theory being, if you can cover all the openings you could create a suction that would hold something down. Till the pump lost prime and wasn't drawing any more. The harder it is to do this, the less likely it is to happen. Obviously one design is far superior to another. Flat is easy to cover, domed is much harder, especially if the openings are spread to the outside edges. It's pretty darn hard to cover all the openings of an anti-vortex cover with just your body. Cloths and bathing suites are different though, and provide an entirely different set of problems. A "T"shirt for example could easily cover off all points of suction, on almost any drain cover. I've tried to cover a running drain (anti-vortex) with my belly just to see if I could, I couldn't , I probably might be able to now, but that's a different story . The only way to completely avoid this awful scenario is to not have a main drain. That is known for sure.

If it was in an underground lateral, I wouldn't want that main drain reopened. But would that main drain lateral be right now open to the other laterals anyway, which would tell us the leakage problem is definitely not in the main drain lateral but rather right at that main drain site? I don't know how everything connects underground. I guess the liner people would/should know?

I'm assuming by "lateral" you mean a line that is connected with another one underground, meaning it does not run directly to your pump suction all on it's own. Yeah your probably right it's not the best scenario to have the main drain "coupled" with another suction line underground and not within your control to divert or change that situation. Smart pool owner.

Here's a some scenarios (assuming a lot about your pool though, ie skimmers and such).


Reason for having a lateral suction line to the main drain: One way of safe guarding against the problem mentioned above (things getting stuck on the main drain) is to have an additional source of suction "coupled" with the main drain. If the main drain became "covered" by something, the other source of suction would prevent it from holding that "thing" down (I hate the imagery so I'll use "things"). Commercial pools are designed this way with two drains any place where one is needed, and far enough apart where one "thing" can't cover them both.

Sometimes in a typical vinyl pool the main drain is "plumbed" into your skimmer body. Check and see if there is an additional "opening" at the bottom of your skimmer. Are there two "holes" at the bottom?. What happens with this configuration is only the additional residual "pressure" in the skimmer body draws a small flow from the main drain (if any). If there are two holes, is one plugged, either with a threaded white PCV plug, or a black rubber plug? If it's plugged with a rubber plug I highly suspect this scenario is how you main drain is plumbed. A plug (black rubber) both in the drain itself and the skimmer body were added when the drain failed. If it's a white threaded plug (sometimes screwed in from below the skimmer), it might not be the case. If there's only one hole in the bottom of your skimmer, then this is not the case (most likely).

The other scenario (much like what your thinking), might exist, especially if your skimmer only has one hole at the bottom. Or has two but one is plugged with a threaded white PVC fitting. That is the suction line for the main drain is connected with another suction line. How many lines end up at the front of your pump, where the suction is? One? Two? If it's only one (and the skimmer plumbing scenario can be ruled out) then yes some where under the ground the main drain line was connected to one of your other "known" suction lines. Where and how not even a pool man might know. Once it's buried it's hard to tell. It could be right under where the lines come up. It could have been the place at which the least amount of pipe was needed to achieve this.

Were you having a hard time keeping the water level in the pool previous to the "Storm"?

Typical symptoms of this scenario of one part of a suction line being bad while another is not are this:

1. Hard to prime the pump (get it going). When the lines have drained back own to the water level (assuming your pump is above that), the leak will now draw "air" from the surrounding ground. Once it get's going it could have enough feed from the the good "section" of pipe to remain primed. Now the water pulls past the leak and into the pump. Thus not letting any "exit" the pool.

2. The pool leaks when it's not running, but doesn't leak when it is running. When the bad suction line sits with out water being drawn past the leak, it slowly leaches water out of the pool. Once the pump is primed and running it creates enough flow to stop this from happening (as described above).

3. Occasionaly bubbles in the pump (not afterwards that would indicate air from another source further down the "line"). If the window into your pump body develops small bubbles sporadically then a source of air is available at some point "infront of the pump. Lots of times it's the threaded fitting at the pump front or a valve, but sometimes it can be a small leak in suction lines that have two "lateraled" sources.

4. Pump loses prime eventually. Same scenario as the bubbles, just more severe and the pump loses prime completely.