Pool Over-Drains After Heavy Rain

[wjmano]

Does the cover have a hole in it like a skimmer cover? If not I am assuming when there is a heavy enough rain that is completely fills the drain pipe it turns into a gravity syphon. This syphoning continues till the seal between the cover and the box dries out enough to break the vacuum.

Simple test would be to leave the cover off when it's rains and see of it happens still. If that stops it, just drill a couple of 1/4" holes in it.

If it continues to happen I am at a loss.

Bill, I think we have a winner!! As suggested, I removed the overflow basin cover last night, ahead of another heavy (2") rain overnight. The pool drained as it should -- to the point where the water dropped just below the PVC riser in the overflow basin, and no more. Thank you for the thoughtful advice -- I would have never came up with this on my own. I'll be drilling those 1/4" holes in the lid later today.

Thanks again!
Bill

 

[Rattus Suffocatus]

Yeah.. beat me to it. I was going to say a siphon was created somehow when I saw the first post. You can try to catch it after a storm and see if you can see it happen or you cold just try to see if there is some way of breaking the siphon and implement that solution preemptively.

 

[phonedave]

Bill, I think we have a winner!! As suggested, I removed the overflow basin cover last night, ahead of another heavy (2") rain overnight. The pool drained as it should -- to the point where the water dropped just below the PVC riser in the overflow basin, and no more. Thank you for the thoughtful advice -- I would have never came up with this on my own. I'll be drilling those 1/4" holes in the lid later today.

Thanks again!
Bill

Just to check something. You said the water ends up about 2" below the top of that PVC pipe. What in your skimmer / fill / drain assembly is also at that height? Your weir door? your skimmer mouth ? Something like that where when the water drops below that level, it would admit air into the assembly and break the syphon.

 

[mcaufin]

Check out Pythagoras' Wine Cup on google or youtube for an interesting analog!

 

[wjmano]

Just to check something. You said the water ends up about 2" below the top of that PVC pipe. What in your skimmer / fill / drain assembly is also at that height? Your weir door? your skimmer mouth ? Something like that where when the water drops below that level, it would admit air into the assembly and break the syphon.

It's hard to say with certainty how low my water level could drop on a consistent basis. It was rare that I turned off my autofill ahead of a heavy rain, so I don't have much experience with this. For now, I've drilled a couple holes in my overfill lid and so far my problem has disappeared. I'm as they say...cautiously optimistic.

 

[atleyjh]

I wanted to say thanks for this. I have a new build with a very similar setup to yours (although my overflow/autofill container doesn’t connect to the skimmer, it’s just next to it) & I’ve been experiencing the same thing. However for me it would only syphon down to about 1/2” below the top of the pipe after heavy rains. I’ll be drilling a small hole into my cover as well.

 

[Bill1974]

It does not take much to seal the cover. It does not take much rain landing on the overflow clover to fill up the gaps between the cover and overflow housing. Even if it's not a great seal, if the rain is heavy enough, it enough water to keep it sealed even if some of it is being sucked into the overflow housing. This is basically the same as the lid on the basket on your pool pump (if the pump is above the pool). If the gasket on the cover leaks, priming the pump is a challenge or maintaining a prime is challenge.