Skimmer Intermittent Suction

[joe_squid]

Trying to help my grandmother get her pool back in order after her husband sadly passed away a few months ago. Pool has been using main drain suction only. If I switch suction to the two skimmers, I start getting a large amount of air in the return lines; one skimmer gets zero suction, while the other skimmer slowly alternates between a moderate amount of suction to no suction at all. Watching this process at the leaf basket immediately prior to the pump, I can see the water level almost reach the top and the pressure on the filter starting to rise, before the water level drops back down and the pressure returns to zero. This process seems to cycle over and over again every 30-120 seconds or so, with the pump basket never quite reaching 100%. I also see a very similar result with the suction set to share between the main drain and the skimmers.

Any ideas on the culprit? I suspect a clog, but it seems strange that I would still get suction through one of the skimmers intermittently. I am ruling out the pump, as everything works fine when on main drain only. Ruling out the filter as well, as I got the same result before and after a thorough cleaning. Water level is sufficiently high and holding the skimmer door open doesn't help either. Looked at lots of other posts but not seeing any relayed to intermittent suction.

Each skimmer has two holes, but one hole in each doesn't appear to be plumbed (dead stop inside).

Her pool is a 30k gallon in ground, with separate pumps for the filter and Polaris, inline chlorinator, Pentair Plus DE filter.

 

[jblizzle]

Well you check the weirs and your checked the water level ... those are the 2 common suspects.

Must be a suction side leak somewhere. Could just be in the valve that controls where the suction is coming from or could be in a pipe (although water lose would be occurring). Or it could be a blockage which is causing the pump to pull in air around its lid.

Can you post a picture of the plumbing setup?

 

[joe_squid]

Imgur: The most awesome images on the Internet

 

[jblizzle]

I was expecting to see 3 pipes. Is the floor one of the pipes and the skimmers somehow tied together?

 

[joe_squid]

I'm pretty sure that's the case.

 

[Pool Amateur]

Just to be sure I understand what you are saying; If bottom drain only feeding the pump everything works fine. If Skimmers only the phenomenon describe above happens. What happens when both the bottom and skimmers are on? If it runs fine, I would say it is a blockage of the skimmers which could also be a valve problem as Jason said above. If it continues to do the phenomenon described above, then an air leak from the skimmers, hopefully from the weirs or low water level. If not have some more investigating to do. Also, if it happens when just skimmers are on, are you sure vale is in correct position and not off, probably not but thought it would be easy to check and easy fix.

 

[joe_squid]

Similar phenomenon when valve is open to both pipes (skimmers and main drain). Any way to test the skimmer weir? I tried holding one of the weirs fully open (the one on the skimmer with intermittent suction) but it didn't seem to make a difference.