Are All Main Drains Created Equal?

[JohnT]

John, if the main drain's function is as a source of water for the pump, where's the source of water if that drain is closed/covered/never opened? Why even have one? It's clearly not pulling water from the pool. I thought the pump recirculates water via the skimmer pvc and the returns?

Water is drawn into the pump from the skimmer(s) and the main drain and sent back to the pool through the returns in a typical pool installation. I'm not sure why a main drain would be installed if it wasn't opened, but it is fairly common to cap one if it starts to leak. Their only function is to provide water to the pump except in gunite pools where they also have a hydrostatic relief valve to relieve external water pressure when the pool is empty.

[elsie]

Interesting. So then e.g., you could dive down to your drain and feel water circulation? I've dived down many times out of curiosity to look through the grate of my drain, wondering what its purpose is. I have my mask on and have put my hand over the grate and looked at the 4 screws beneath it that presumably keep the cover on. There is no draw from that drain. It is completely closed. That's why I assumed it's function was to drain the pool. Of course the more I think about it, that's not even logical, because if there's that kind of suction from the drain when opened, even a diver would be in peril.

So if there's circulation there, in other pools, that means the cover is off? Why doesn't it suck people to it? In this commercial kiddie pool where the girl was almost fatally injured (and whose life is forever altered) why would the drain be closed in the first place if its function is to add to the circulation of water?

Sorry for all the questions, John, but still confused.

[KurtV]

elsie,
Depending on how your pool is plumbed, you may have a valve that controls flow from the main drain. If that's closed, you won't have any suction there. As JohnT said, your drain could also have been intentionally capped because of a plumbing leak. It could also just be plugged up with something.

Modern pool drains have anti-vortex covers that minimize the sucking force generated by the flow of water. Main drains are also installed in interconnected pairs that are placed a couple of feet apart so that, without being extremely large or extremely flexible or both, a person can't seal off the main drain and become entrapped. There's still some danger though as one of the main drains could be blocked by something (deflated pool toy comes to mind) renedering the other one a hazard to an incautious swimmer. The anti-vortex cover would still make entrapment unlikely but it's definitely possible in such a scenario. Couple one blocked main drain with a missing or old style cover on the other and you've got a tragedy waiting to happen.

I generally keep my main drain valve at the pad closed. I do that as a safety precaution and to maximize flow through the skimmers.

[JohnT]

Interesting. So then e.g., you could dive down to your drain and feel water circulation?

So if there's circulation there, in other pools, that means the cover is off? Why doesn't it suck people to it? In this commercial kiddie pool where the girl was almost fatally injured (and whose life is forever altered) why would the drain be closed in the first place if its function is to add to the circulation of water?

Sorry for all the questions, John, but still confused.

You can't feel the suction. All main drains are supposed to have a cover on them, but the water flows through the cover. A common design for the cover is a raised flat surface with the openings around the edge. It looks solid from above. Go to this link for drain info and pictures: http://www.drainsafe.com/print_summary.htm

[cleancloths]

Here is a picture from the above page:



with a cover like this it would be almost impossible to have an accident like the one talked about.

[elsie]

Thanks all. I understand better now. The cover by definition, contrary to what I was thinking, does not necessarily preclude water intake, but rather by design mitigates the intake as I see in the picture (depending on the situation with the valve below it). And that's just how my cover looks, although I'm not sure I can visually see those vertical sides, but I do see the plate and screws.

It would be interesting to know the history, i.e., why mine does not function as part of an integrated whole. Maybe a leak as suggested. It's also worth noting that apparently whether or not that main drain is completely closed off or not doesn't seem to affect the efficiency of water circulation, or problems associated therewith. Of all the posts I've read, I've never read "yeah, my main drain is closed because the valve leaks so I don't get good circulation and tend to get algae."

So back to a chicken-and-egg thing, if the circulatory system works fine without use of the main drain, why did they install them in the first place? And do they still?

[cleancloths]

There is a lot of arguement as to if they are needed or not. In a "Perfect" engineered design you probably don't need one. But, most pools are far from perfect and having one will improve circulation and help maintain a much more steady temperature. Remember that heat rises, so the bottom of the pool will tend to be much colder. By pulling the cold water off the bottom you mix it better with the pump and eliminate thermal gradients in the pool, not to mention circulating chemicals better.

If there were no reason for them you can be certain contractors would not install them as they cost money.

[elsie]

I think the pic Cleancloths posted is mine:

Sta Rite 8" Anti Vortex 0712-0741

Manufacturer: Sta Rite

Maximum Flow, ANSI/ASME A112 Rating
60 GPM

This cover is A112 approved at 60 GPM

The Sta Rite cover is flat on the top with a circle in the center. Water is drawn in on the elevated sides..

_________________

If the valve were open, I would not be able to feel water being pulled in? SO maybe mine is open after all? I'll dive down this weekend with a vial of dye to see, just for the heck of it.