Where does the air bubble come from?

[michael6866]

Hi,

My 24,000 sq ft ingroud pool has two skimmers and one main drain and several return jets. Recently I observed air bubbles in both return jet and pump strainer. So this implies the issue is somewhere before reaching the pump(or the pump itself - but I've ruled out the case, see below).


The experiments:
(1) If I use the return line diverter valve to shut down the skimmer return line(the main drain return is still open), then there is no bubble in the pump strainer nor the return jet. I guess this rules out the main return line leaking, right?
(2) Then if I restore the return line diverter position(half main drain + half skimmer) but close the caps inside both skimmers, then there is no bubble. So this rules out the skimmer return line leaking, correct?
(3) If I open either of the skimmer cap, then the bubble comes up in both the pump strainer and the return jet.

Now I can only think of two things:
(a) Is the weir door stuck so that not enough water gets filled in? No, because the issue remains even if I remove both weir doors.
(b) Is the water level low? I don't think so since the water level is about 2/3 or more in the skimmer.


Could there be any other reasons? What should I check next?

Thanks,
Michael

 

[Richard320]

(b) Is the water level low? I don't think so since the water level is about 2/3 or more in the skimmer.

Do you see vortex in the skimmer? You know, a whirlpool?

 

[michael6866]

No, there is no vortex. I also tried removing the weir door so that the water doesn't flow too fast into the skimmer. But it doesn't help either.

 

[satpoolman]

If possible, post pics of your equipment pad and plumbing/valves to aid us in troubleshooting your issue.

Regards,
E

 

[michael6866]

I called my local pool store today and they said another reason could be that I added too much DE power. So they asked me to do a backwash. Does that make any sense? My DE filter is running at 12~13 psi currently so I don't see the point to do a backwash.

 

[michael6866]

water level, water level in the skimmer, and the skimmer cap I mentioned.

 

[michael6866]

It seems I exceeded my quota. Below are links to the other images:
My return line diverter valve: IMG 1003 — imgbb.com
My DE filter pressure: IMG 0996 — imgbb.com
No bubble in the pump strainer when diverter shuts off the skimmer return line, or when the cap blocks the skimmer hole: IMG 0999 — imgbb.com
Bubble comes up in the pump strainer when diverter is 50/50 and skimmer cap is not blocking: IMG 0997 — imgbb.com
Bubble comes from the return jet: IMG 1002 — imgbb.com

 

[satpoolman]

(1) If I use the return line diverter valve to shut down the skimmer return line(the main drain return is still open), then there is no bubble in the pump strainer nor the return jet. I guess this rules out the main return line leaking, right? Right, no air leak in your main drain line.

(2) Then if I restore the return line diverter position(half main drain + half skimmer) but close the caps inside both skimmers, then there is no bubble. So this rules out the skimmer return line leaking, correct? No. This is just another way of doing what you did in Step (1).

(3) If I open either of the skimmer cap, then the bubble comes up in both the pump strainer and the return jet. You have an air leak in your skimmer line, somewhere from the Jandy (diverter) valve to the skimmer plumbing T-junction.

Look at all of the skimmer line plumbing joints from your Jandy (diverter) valve to where it goes into the ground. Look for hairline cracks in plumbing fittings as well as pipes. You can use Foamy shave cream to apply to plumbing joints while the pump is running - air leaks will reveal themselves by sucking in the Foamy, some as small as pin pricks. Hope this helps.

Regards,
E

 

[michael6866]

Hi satpoolman,

Thank you for your reply. However I don't quite understand your answer to (2) as I think it's different from (1).

I assume the normal flow is like this: skimmer ---> skimmer line ---> diverter ---> pump strainer ---> filter ---> ...

In (2) I block the skimmer with the cap and leave the diverter 50/50. If what you saying is true that the skimmer line has a leak somewhere, then I assume I should be able to observe air bubble in the pump strainer because the pump would suck in air from the leak. What am I missing?

Thanks,
Michael

 

[satpoolman]

Hi satpoolman,

Thank you for your reply. However I don't quite understand your answer to (2) as I think it's different from (1).

I assume the normal flow is like this: skimmer ---> skimmer line ---> diverter ---> pump strainer ---> filter ---> ...

In (2) I block the skimmer with the cap and leave the diverter 50/50. If what you saying is true that the skimmer line has a leak somewhere, then I assume I should be able to observe air bubble in the pump strainer because the pump would suck in air from the leak. What am I missing?

Thanks,
Michael

Sorry for any confusion, I'll try to explain a little better.

Putting your diverter 50/50 then closing the caps in both skimmers is the same thing as fully shutting down the diverter skimmer line and leaving the main drain line 100% open. I wish I knew how to use a computer draw program to illustrate this point more clearly.

If you focus on my answer to #3 you'll find your problem.

Regards,
E

 

[michael6866]

I applied the Shavy foam to all joints from the diverter to the ground. No suction observed.

I still don't understand your answer to (2). Let's exaggerate that a little bit - assuming there is a really big hole(e.g. baseball size) in the diverter skimmer line, then according to what you say I will not observe any air bubble in the pump strainer if I only close the caps in the skimmers while leaving the diverter 50/50. How could it be possible that the big hole doesn't suck in any air? Please bear my stupidity..

 

[michael6866]

The guys from the pool store came today and they didn't find any leak above the ground either. They suspect the leak may be under the ground. They will perform a pressure test later this week. I'll post once there is any update.

 

[michael6866]

Update: The pool store did the pressure test today and the result indicates there is a small leak somewhere in the skimmer line under the ground. But they couldn't locate the exact location of the leak. So for a fix they have to replace the entire skimmer line which would cost around $1k. They suggest living with it for now as the pump doesn't loose prime.

I told them my major concern is whether the air would damage the pump. They said as long as the pumper doesn't loose prime then I don't need to worry about it. Is it true?