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Thread: Trouble Shooting Question w video: Will leak cause cavitation?

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  1. #1
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    Default Re: Trouble Shooting Question w video: Will leak cause cavitation?

    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.
    Last edited by AlgaeFarmer; 07-27-2016 at 01:09 PM.

  2. #2
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    mas985 is offline Lifetime Member Whizbang Spinner mas985 3 stars mas985 3 stars mas985 3 stars
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    Default Re: Trouble Shooting Question w video: Will leak cause cavitation?

    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)
    Impossible.

    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 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.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

  3. #3
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    Default Re: Trouble Shooting Question w video: Will leak cause cavitation?

    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.

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