I have a return line coming from the skimmer and one from the main drain. There is a 2.5 psi pressure difference between the two (with main valve closed, pressure is 14.5 psi; with skimmer valve closed, pressure is 12 psi). Should the pressures be equal? If I close the skimmer valve 1/2 way (45 degrees) the pressures equal out (I get 14.5 psi and the flow through the skimmer is good).
More to the story: Pool's been open for over 6 weeks. Water is clear. I bought this house with the pool 4 years ago. The skimmer line collapsed 2 years ago (it was flex line). I replaced it with schedule 40 PVC. After opening the pool this year the area around the main drain has stayed kind of discolored (brownish green ring around it). Lately the liner seems to be getting some light brown color to it in the shallow end. I seem to have a hard time keeping the chlorine level up. When I close the skimmer valve I notice some air bubbles coming through the main drain return line to the pump. My fear is the main drain line is starting to collapse and I'm not getting enough flow through it.
Filter pressure readings are:
17 psi with both valves open (no bubbles)
12 psi with skimmer valve closed (noticeable bubbles coming into pump)
14.5 psi with main valve closed (no bubbles)
15 psi with main open and skimmer valve 1/2 closed (turned 45 degrees)
Question - Should I run it with the skimmer 1/2 closed to try to balance the pressures and get more flow through the main drain or should I keep both valves fully open? I'd like to limp through this season as best I can and replace the main line after this season is over.