Air In Pump Question

[cdoz35]

Hello everyone. I have been a 2 year reader of the forums and want to thank everyone for the wealth on knowledge available on this forum. There a truly some amazing people, that probably don't realize how many people they have helped by answering questions, and then other people with similar problems also head the advice. I recently joined the forum, and want to tell you a little bit about my pool, and the problem that I cannot seem to figure out.

We moved into a new house last year, that has a 80s model inground gunnite pool. The pool was not in the best shape, but I have been able to get it in operating condition. It could probably use a new coat of plaster, but it holds water good as it is and works great in this Texas heat to cool us off. I have been using the BBB system and could not be any happier. The water has stayed clear and clean. What a awesome trouble free system. As long as I put a few minutes in each day the pool has stayed in tip top shape.

Anyways I have a problem that for the life of me I cannot get figured out. The pump is getting air in it, but I can't make sense of where it could be coming from. Let me tell you about the setup.

The pool has one main drain, and one skimmer. Both return to the pump station through their own 1 1/2 pvc pipe. When they arrive to the pump station there is a Jandy valve that allows me to select to pump from the skimmer, the main drain, or both at the same time. This is where I am dumbfounded. I get very little to no air bubbles in the pumps filter basket if I am drawing from both sources at the same time. However, if I switch to just on or the other I am getting a lot of air into the pump, sometimes enough to almost loose prime. This makes it very hard to run a pool vacuum, because I cannot divert the full pump suction to just the skimmer without getting a lot of air, and I do not want to ruin my pump.

I have checked every thing I can think of. I have disassembled the Jandy valve and checked the O rings in it, and they all seem to be in good shape. I have checked the fitting where the plumbing runs into the pump and cannot find any problem there. I have also double and triple checked the filter basket o ring. I have tried to run water over all of the fittings and cannot get anything to change. Correct me if I am wrong, but I feel like the suction side leak has to be coming somewhere between the jandy valve and the pump, or I would not be sucking air from both the skimmer and the main drain. I am thinking that when I have both sources open the pump is not having to suck as hard, so it is not sucking in the air as bad.

Maybe I am looking at this all wrong, any advice or things to check would be greatly appreciated.

One more thought I had, but I think it is probably far fetch. The pump has done this ever since we moved in, so I don't have nay background on it. Is there a chance that the pump is too over sized to pull through just one 1 1/2 pipe at a time, that it is causing cavitation which would lead to the air bubbles? I know this is far fetched, but I wonder if it could be a possibility.

Thanks in advance for any advice

 

[chiefwej]

The fact that it only happens when one line is open does not isolate it to the area past the valve. Anytime you draw from only one source you are increasing the suction on that entire line. But the fact that it occurs when either line is selected is rather telling, so yes, I would concentrate my search in the area of the valve and line fron there to the pump. Two valuable tools when searching for a suction leak are old fashioned shaving foam and plastic food wrap. Smearing shaving cream on a suspected leak and watching for it to appear in the pump pot, it one method. Food wrap can provide a temporary seal by wrapping valve or pipe joint you suspect and seeing if the problem goes away.

Pump cavitation is something completely different and doesn't result in air in the pump pot. It happens when supply is so restricted to the pump that it draws enough vacuum to actually boil water at low tempratures. Bubbles first form and then collapse at the impeller of the pump. It sounds like there are marbles banging around inside the pump, and it can do real damage.

 

[cdoz35]

After further research I agree it is not cavitation. So back to the search for the leak. Thank you for the ideas to try, and confirming my suspicion that it is probably wither in the 3 way valve or between it and the pump. If I can't find it by testing maybe I will just replace it all as it is all pretty old anyways. Thanks!