At this point also in centrifugal because of high rpm since it is directly coupled to electric motor the pump Centrifugal Vacuum Pump creates partial vacuum which means the liquid can flow through vacuum therefore the liquid will be recieved in the centrifugal pumps suction and since the impeller rotates the liquid will be displaced away 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, hence reducing the air pressure build-up created by blow because of combustion gases going past the piston rings into the pan.