At this point also in centrifugal because of high rpm since it is directly coupled to motor the pump creates partial vacuum which means the liquid can flow through vacuum therefore the liquid will end up being recieved at the centrifugal pumps suction and because the impeller rotates the fluid will be displaced aside forward with a specific energy.
A vacuum pump gets the inlet hooked up to 1 or both valve covers, sometimes the valley pan. It SUCKS the air from the engine, thus reducing 
the air pressure build-up created by blow because of Centrifugal Vacuum Pump combustion gases going at night piston rings in to the pan.