Cavitation? Or Leak?

[nmqjstl]

I have all brand new equipment on my pool pad. The pump is a Hayward Tristar 1.85 THP. Unfortunately I am getting air bubbles in the pump basket and I am unsure if it is cavitation or a leak, either coming from the plumbing or from the pump itself. I have someone coming to do a leak test on the plumbing, but they can't get to me for a bit longer. I have put some Magic Lube on the pump lid o-ring as well as the o-ring for the unions. Here is what I can observe:

- The pump sounds "normal" - I am not hearing anything that sounds like rocks rolling around in the pump
- If I run the pump at 3000 RPM or above - I can see bubbles here and there but an air bubble does NOT form in the pump basket
- If I run the pump less than 3000 RPM - after some time a significant air bubble will up in the pump basket
- Regarding the last two points, while I originally believed running at higher RPM "fixed" the problem - I think it likely is just masking it - I think the air bubble is simply building up inside the filter instead of the pump basket at higher speeds
- Running at 3000 RPM I am moving 55 to 60 GPM with pressure reading about 14 PSI.

Any theories on cavitation or leak based on the information above and videos below?

First video is running at 2500 RPM where the air bubble building in the pump basket

Second video running at 3000 RPM - can see little air bubbles but no build up of a large bubble (at least not in the pump basket)

Thanks!!

 

[Jimrahbe]

N,

Air bubbles under the pump lid is quite normal at a lower RPMs. As long as the bubble does not keep getting bigger and bigger.

That said, this should not be a big issue when running at 2500 RPM or higher.

Show us several pics of your equipment pad so we can see how things are connected..

Thanks,

Jim R.

 

[nmqjstl]

It gets bad at 2500 RPM:

I'll try to get some photos of the overall pad but it is raining now....

 

[nmqjstl]

Just came across the Hydraulics 101 Forum by @mas985 - it says "Cavitation cannot usually be directly observed because it occurs at the impeller inlet which is blocked from view" and "these vapor bubbles do not exist for very long and as they travel through the impeller, the pressure rises and the bubbles rapidly collapse causing a very distinct sound much like small pebbles traveling through the pump"

So, now I am back to think it is a leak????

 

[mas985]

Yes, more than likely a leak. Lube the pump lid gasket and drain plugs to help seal them.

 

[Pool_Medic]

If it is in fact a leak then when you turn the pump off you should witness the water leaving the pump basket quite briskly. Every one of my pools with VS pump has a bubble at lower speeds.