Bottom drain mystery

[scader]

I have an inground where the bottom drain feeds into the bottom of the skimmer bucket and then combines with skimmer water to a single line to the pump. Sadly, this gives me no control over bottom vs skimmer. I was curious to see how well the bottom drain worked, so I covered the pool-side of the skimmer intake with the skimmer cover (worked better than I expected). Also unexpected: the pump ran dry, even with standing water in the skimmer bucket. I'm not sure how that's possible, but my question is should I expect the bottom drain to be able to feed enough water by itself, or does the pump running dry imply a blockage in the bottom drain? When the pool company winterized the pool last fall, I watched them blow out the bottom drain line without issue.

 

[scader]

So I think I know what's happening. First, when I cover the skimmer, the pump sucks all the water out of the skimmer. Right as it gets to the bottom of the skimmer, you can see water coming up out of the bottom drain--so it is moving water. During that process, too much air gets sucked into the return that it doesn't have enough suction to pull from the bottom drain. The pump goes dry, and then the bottom drain partially fills the skimmer to the water level.

To test this theory, I turned the VS pump on low, and sure enough it pretty much kept up...you could far better see water pulling up from the botttom drain to refill the skimmer bucket. It was still too much suction and eventually ran dry.

So I guess that answers my question. The bottom drain is working, just can't feed the pump alone.

 

[Jimrahbe]

S,

Almost no one needs an operating main drain.. There are thousands and thousands of old pools where the main drain is plumbed into the bottom of the skimmer and they all work just great.

In most cases, depending on the actual skimmer, you need a floating diverter valve to make the main drain work.. Most of the old pools no longer have the floating valve, and therefore no longer have use of the main drain.

how a floating valve work in a skimmer video - Google Search

I have never been able to get the seal working well enough to trust the floating valve to work for more than a few minutes..

Thanks,

Jim R.

 

[Richard320]

 

[scader]

Good to know. Thanks for sharing the information and the video/animation to help demonstrate.