My pool consists of the main body of pool water along with a spillover spa. Both Spa and pool share the same equipment and is the same body of water.
The problem I am experiencing is a surging of intermittent air coming out of the returns. When in "pool" mode it is barely noticeable, just a few air bubbles occasionally escaping from the returns closest to the equipment (shallow end).
But when in full spa mode (i.e. only spa returns are open) it is VERY noticeable. A few seconds of a steady water stream, followed by a few seconds of a blast of air bubbles.
There is no audible surge coming from the pump. It has a nice steady hum. Also note that if I hold my hand in front of a return jet, the outflow is the same steady flow throughout. There are no air bubbles in the pump basket. I have checked for pressure side air leaks to the best of my ability. I have also lubricated all o-rings at pump connections.
When I turn off the pump, I look to see if any water "spits" from any of the connections (i.e. pump basket, pump drain plug, connections where the PVC meets the pump housing, etc). Nothing. No spitting.
It is my understanding that air returning into the pool HAS to be a pressure side air leak. Am I wrong? Is there anything else I may be missing?