Today also in centrifugal because of high rpm since it is directly coupled to electric motor the pump creates partial vacuum this means the Centrifugal Vacuum Pump 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 aside forward with a specific energy.

A vacuum pump gets the inlet hooked up to one or both valve covers, sometimes the valley pan. It SUCKS the atmosphere from the engine, thus reducing the surroundings pressure build-up created by blow because of combustion gases going past the piston rings in to the pan.