I have a vacuum vessel that is half full of water and -0.7 bar vacuum maintained above it. I am constantly filling the vessel with cold water and removing it with a centrifugal pump. The tank outlet is on the bottom that runs down about 3 feet to the inlet of the pump. There is a small line (1/2" or so) that connects the top of the vessel to the pump discharge, balancing the pressure across the pump. My question is what pressure should I see at the pump inlet with -0.7 bar vaccum in the tank above and the pump not running? Should I still see 36 inches of water pressure, or does the vacuum have an effect? Also, when the pump is running, should I still see pressure there (maintain NPSH on the pump)?