Trouble Shooting Question w video: Will leak cause cavitation?

Howdy!
I have a Challenger 1&1/2HP, pieced a repaired over the last 25+ years. The pump has run dry a couple of times this winter and spring. The basket was hot but nothing appeared to be warped. The pool does not have a main drain (prior owner plugged), therefore the skimmer is the only source of water intake and prone to clogging.

Water: I told chemistry is good, but have had chronic issues maintaining enough chlorine to keep the water from turning green. During this time I've been dogged with pool circulation and filtering issues.

The pump has been priming then quickly (about 30 seconds) losing vacuum with the water level inside the trap dropping quickly. while this is happening the pump is loudly cavitating and struggling to prime itself. Then it finally catches up only to quickly develop another bubble and frustratingly drop out again only to repeat this again and again.

As you can see there is a constant bubble under the clean out cap. This morning I checked the seal of the Jandy valve on the intake side and the o-ring appeared to be good. I then unscrewed the outlet pipe from the pump, cleaned off a lot of residual sealant, cleaned male and female threads and applied plumber's tape to the pipe's male threads. Applied sealant to the lip of the pumps outlet port. Then slowly screwed this joint back together and smoothed the pressed sealant from the joint.

Over the last several years a leak has developed behind the pipe linking the pump and sand filter. Could this leak at the impeller housing be causing air to be sucked in as well causing cavitation inside the housing, loss of vacuum, dropping of water level inside trap and my frustration too???

A person familiar with the pool thinks the pipe attachment to the skimmer has detached and a cavity has formed around that open joint. This might explain the symptoms, but I do not get root material or dirty water and the above steps seem to have decreased the severity of the problem. Although, the leak is still there, the bubble is persistent and cavitation is still audible. Hope that all makes sense.

Sorry wasn't able to upload the video. The water leak appears to come from the area directly behind the exit pipe, near where the two pieces of the impeller housing are held together by the tensioning band.

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Originally Posted by AlgaeFarmer

The pump has been priming then quickly (about 30 seconds) losing vacuum with the water level inside the trap dropping quickly. while this is happening the pump is loudly cavitating and struggling to prime itself. Then it finally catches up only to quickly develop another bubble and frustratingly drop out again only to repeat this again and again.

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This is indicative of either a stuck weir in the skimmer or your water level is too low. While this is happening, look inside the skimmer and see if there is vortex forming and sucking in air.

mas985, Thank you for your reply. The weir operates correctly and the water level is good. The skimmer pot is not emptying. In fact, both the skimmer pot and catch basket on the front of the pump-housing can be filling when the pump begins to cavitate.
Upon first starting the pump it will prime itself, the catch basket will fill completely, the sound of the pump becomes a nice hum with only a single small bubble or no bubble at all under the plastic cleanout top. About 30 seconds later the impeller begins to whine then whitewater under the cleanout cap, then the circulation slows, but water is still entering the pot throughout this process. Circulation continues within the cleanout pot, but is slowed and slowly rises while spinning until primed again...and repeat.
I've replaced exposed PVC on the wet side and on the push side from the pump to the sand filter, lubed the cleanout cap and o-ring, even replaced the front half of the volute where there had been a stress crack. Tightened my tension band around the volutes to 1/4" per the user's manual. A pool guy came over to troubleshoot yesterday, advised the PVC work that I did and mentioned the possibility of a leak underground.

At this point I've looked at this thing so many times that I'm starting to see anything that is POTENTIALLY wrong.

I'm not writing off the possibility of an underground leak, but the problem with that is that water flow never stops (actually there are rare instances where the line will "chug" once or twice and immediately begin to flow again, but this is rare)

Is there any chance the RPMs turned out by the pump are causing the impeller to spin faster than it is designed to work at? (wild guess)
What about the impeller wear, I've checked it out and made sure it is clean, is there some symptom I might be missing?
I've also checked the large o-ring in the volute seal and the smaller O-rings at the intake of the volute and tightened the tensioning band.

Even the professionals seem stumped.

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Is there any chance the RPMs turned out by the pump are causing the impeller to spin faster than it is designed to work at? (wild guess)

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Impossible.

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What about the impeller wear, I've checked it out and made sure it is clean, is there some symptom I might be missing?

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I don't think that would cause the issue.

Sounds like an air leak but why it would be periodic if isn't a weir or water level, I do not know. Sometimes, suction side leaks will pool around the broken part of the pipe and so will appear to work for a while as the water is drawn back into the pipe but after than happens, it should just suck air.

Thanks again. I've had a couple of other people look at it. They think the line from the skimmer to the pump is either cracked or blocked. This is an older pool and currently the skimmer is the only source for the pump to draw water from. This is also true for vacuuming. I've dealt with blockages before, but this one (if that is what this is) is different due t the amount of water that is reaching the pump. As stated the cleanout pot is never empty and circulating water is always present...it's just that circulation and water level is diminished.

Interesting note. When I place my head to the ground about the area that a PVC elbow joint should be I can hear a lot of swishing and bubbling noises. Closer to the skimmer I hear a gurgle from time to time. We'll see. A pool guy is coming out tomorrow to pressure test the line and then blow it out if able. Trying to locate a plumber that can scope the line also. to see what we're dealing with.