Now also in centrifugal because of high rpm since it is directly coupled to electric motor the pump creates partial vacuum which means the liquid can flow Centrifugal Vacuum Pump through vacuum therefore the liquid will become recieved at the centrifugal pumps suction and since the impeller rotates the fluid will be displaced aside forward with a specific energy.

A vacuum pump has the inlet hooked up to 1 or both valve covers, sometimes the valley pan. It SUCKS the air flow from the engine, therefore reducing the air pressure build-up created by blow because of combustion gases going at night piston rings into the pan.