I purchased a 4 year old home in FL last year with an inground gunite pool. The pool has 3 ball valves, one for each of the two skimmers, and the third one is for the 2 bottom main drains. If I open the main drain valve (partially or full), the water in the basket section before the pool pump drains out and the pump loses prime. This happens as soon as I start to open the main drain valve. I cannot get prime back unless I close the main drain valve and have one or both of the skimmers on.
It does this whether the pump is on or off, and if the skimmer valves are open or closed (either one of both of them) and with the pump on or off.
I had a pool guy for a year since I bought the house, and he never said anything about the main drain not working. He has always had the main drain valve turned off. I found the problem when opening/closing the valves to better understand how the pump operates.
Hoping someone can help me solve the problem, and that it will not be a major repair cost. Thanks in advance.