Hoping one of the gurus here can help.
I've got a system with 2 skimmer lines and a main drain line feeding into the pump intake. When I have the Jandy valves set so that the pump only pulls from one or both of the skimmers, I have no issues getting primed.
However, once I switch the skimmers off and try to use just the main drain, I can't seem to maintain prime. It will churn for a while, some water will come out slowly at first and then flow rather quickly like it's about to fill the pump basket like normal, but before the bubbles and turbulence settle down and go normal, the water flow drops dramatically and then it churns and churns again. After about another 30 seconds to a minute, the whole cycle will start over and it will look like the pump is about to prime finally but then flow drops again. Oddly, if I have both skimmers and the MD turned on, then it can also maintain prime.
Things I've tried:
Replace the o-rings in the Jandy valve for the MD -- No luck
Replaced the pump basket T-Seal -- No Luck
Pump Drain Plugs checked and tightened -- No Luck
PVC Connections -- Checked and no signs of cracking or leak. Wrapped all the visible, above-ground PVC connections from MD to Pump in Electrical Tape -- No Luck Also tried the running water over the junctions and no luck.
Nothing seems to make a difference so I'm leaning towards it being a PVC leak somewhere under ground, but was curious given the cycle where MD almost primes then flow backs off, almost primes then flow backs off, etc. if that could be an indication of something else.
Pump is a Northstar 2 1/2 HP variable speed.