I believe a siphon has developed in my pool overflow. We recently had the skimmer replaced, and all the pool equipment re-plumbed. But the overflow is original. (The skimmer is a 2-hole type, one goes to equipment, the other to the overflow which is an above-ground 2" PVC with a hole at the desired level.) Anyway, everything was fine until we had our first big rain and the pool reached the overflow point. At first, it appeared to be OK, but then we realized it continued draining past the normal fill line. We can cap off the overflow either at the bottom of the skimmer or cover the hole on the pipe itself (which is what we are doing because it is easier.) However, this means we need to be at home to remove the cap when we have heavy rain and then be here to put the cap back on. I'd like to figure out a better solution, like how to permanently stop the siphoning. Any thoughts?
Overflow is siphoning past the fill line
- Thread starter barbccfl
- Start date
- Jul 21, 2013
- 66,101
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Welcome to TFP.
We have no way of knowing what is happening without seeing pictures and diagrams of your overflow line and its routing.
The overflow should stop when the pipe is no loner underwater. Have you observed water coming out of the overflow pipe when the overflow inlet is not underwater?
We have no way of knowing what is happening without seeing pictures and diagrams of your overflow line and its routing.
The overflow should stop when the pipe is no loner underwater. Have you observed water coming out of the overflow pipe when the overflow inlet is not underwater?
The overflow is direct from the bottom of the skimmer to a pipe that has a hole drilled at the desired overflow level. See the image I created, Skimmer Cutaway. We added a coupler and a piece of pipe to the overflow to see how high it would go. It went several inches higher into the extended pipe, and we observed it pulsing as if the water was surging and retreating. I'm now wondering if the overflow is seeking the level of our spa, its water level is several inches higher than the pool. The water in the overflow pipe continues to pulse even when the equipment is off. I have attached a diagram I made of our pool/spa setup, I'm sure I left off some details but it is pretty close. I'm still wondering if there is a siphon happening. The pool equipment does sit higher than the pool fill level. As I said in OP, this started after a re-plumb AND heavy rain that triggered the overflow process for the first time after the re-plumb.
Attachments
- Jul 21, 2013
- 66,101
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
That is not a good design since you do not have an air gap to stop the siphon when the water is at the desired level.
That second bottom hole in the skimmer is not used for an overflow. It is used to connect into a main drain.
A hole in the top back of the skimmer is typically used for the overflow. Many skimmers have an overflow knockout hole that can be opened for this purpose.
The water then flows out the overflow hole until it gets to a level below the hole as shown by the yellow line. There will be no siphon since air will be at the hole when the water is below the overflow level.
That second bottom hole in the skimmer is not used for an overflow. It is used to connect into a main drain.
A hole in the top back of the skimmer is typically used for the overflow. Many skimmers have an overflow knockout hole that can be opened for this purpose.
The water then flows out the overflow hole until it gets to a level below the hole as shown by the yellow line. There will be no siphon since air will be at the hole when the water is below the overflow level.
There is a concrete block retaining wall between the pool and the overflow pipe. I suppose a small hole could be drilled through the block and into the skimmer as in your drawing. What's interesting is the old skimmer also had two holes, but one was capped off, the one that is plumbed to the overflow. So, as far as I know, this pool never had the skimmer plumbed to the drains. And, we are now guessing the reason the 2nd hole was capped off was because the overflow was siphoning.
The reason we replaced the skimmer (original from 2006) was because a leak was detected in the skimmer. It may be the leak was high enough for a long time that it worked as the overflow. But a few months ago the pool started losing an inch a day which led to the discovery of a long crack in the skimmer that extended below the usual waterline.
I think the conclusion here is the overflow is a bad design and there is no practical way to break the siphon. Instead, we will cap it off permanently and put in a new overflow method. For pools that are flat on the ground, where/how is the overflow plumbed?
The reason we replaced the skimmer (original from 2006) was because a leak was detected in the skimmer. It may be the leak was high enough for a long time that it worked as the overflow. But a few months ago the pool started losing an inch a day which led to the discovery of a long crack in the skimmer that extended below the usual waterline.
I think the conclusion here is the overflow is a bad design and there is no practical way to break the siphon. Instead, we will cap it off permanently and put in a new overflow method. For pools that are flat on the ground, where/how is the overflow plumbed?