I think I have an air leak in my lines. Please tell me if my logic is sound here...
If I set the valve to shut off the skimmer (just pull from the main drain), and crank the pump up to 3400 rpm, I get all kinds of air in the basket.
Open the valve up just a little, so it pulls a little from the skimmer and all the sudden the pump basket fills right up to the top (with just one big bubble there). Shut the skimmer side off again and back comes the air.
Once the pump goes back down to my "normal" setting (2200 rpm) and no problem with the skimmer completely shut off.
If I close the main drain completely I get a little of the same type behavior, but nearly as bad.
So...here's my thinking...
I've got a leak in the main drain line. When I crank the pump up, it really sucks it in, but normally there's not quite enough vacuum to "overcome" the bad seal where the leak is (at least not quite so visibly). When I open the simmer side, even a little, it cuts the suction force down in the main drain line so that it's not quite powerful enough to pull in all that extra air.
How's my logic? Or did I miss the boat completely on this?