Air bubbles and a bunch of racket??

[NurseRatchet]

Hello all! Long time lurker here. I am usually able to find the answer to any question I have just by searching, but alas I am stumped and may need a bit more help than that.

The past few months, whenever I am pulling suction on the "Main Drain" line, the pump makes a terrible racket and bubbles appear in the filter basket, which is resolved by shifting the valve back toward Skimmer. Here is what is stumping me...I believe the bubbles are being formed by cavitation vs. an air leak. The bubbles just appear (rather than flowing into the basket), and there isn't enough air to lose prime or anything. I still have water flow, perhaps at a very slightly reduced pressure when I open the spigot valve located on the pump outlet.

Pertinent Equipment:
There is a valve that separates Main Drain from Skimmer (I have two skimmers, 2 deep end drain covers, 4 wall drain covers, and two hot tub drain covers) before inletting to the filter pump.

So I'm thinking clog somewhere, somehow. Now, before I drag out the toilet snake, I figure I maybe should solicit ideas on how to resolve this? My pool is 53 degrees today, so I won't be diving in and removing covers without being armed to the teeth with validation or advice. LOL

Thanks a bunch in advance!

 

[mas985]

Cavitation won't cause air bubbles that you can see in the pump basket. Cavitation causes vapor bubbles that only exist close to the impeller. As soon as the bubbles move away from the impeller inlet toward the outside of the impeller, they collapse very quickly. However, high suction can cause both cavitation and air leaks.

Also just because the air bubbles show up in the basket, doesn't mean you don't have an air leak. That is more than likely caused by an air leak in the pump lid. When the suction increases, due to a suction side blockage, the pump lid has a hard time remaining sealed so it tends to leak. Also, the drain plugs can leak air.