Now also in centrifugal due to high rpm since it is directly coupled to electric motor the pump creates partial vacuum which means the liquid will certainly flow through vacuum therefore the liquid will be recieved in the centrifugal pumps suction and as the impeller rotates the liquid will be displaced away Centrifugal Vacuum Pump forward with a specific energy.

A vacuum pump has the inlet hooked up to one or both valve covers, sometimes the valley pan. It SUCKS the air from the engine, therefore reducing the air pressure build-up created by blow due to combustion gases going at night piston rings in to the pan.