Pump priming subtlety
I have read every pump priming thread I can find here, but I have a question about my situation that they didn't seem to address. My Shurflo w/accumulator has always been able to prime and pump when there is low or no pressure in the system, but it takes an awfully long time to shut off by itself. Then it seems to lose it's prime and can't get it back until the system is nearly drained again. I replaced the pump a year ago (not knowing about the vacuum situation), so it should be working OK.
So tonight I sucking water up from the tank with my mouth successfully, and was able to blow bubbles in the tank, too. But with pressure in the system, the pump still wouldn't draw water from a glass. I still plan to replace the screen filter assembly and one of the supply hoses that has seen better days, but I will be dismayed if I do that and still have the same problem.
Can priming only be done with low or no pressure in the system? Is this normal, or am I missing something? Any suggestions would be appreciated.
(1974 International Overlander twin bath)