Now also in Centrifugal Vacuum Pump centrifugal due to high rpm since it is directly coupled to electric motor the pump creates partial vacuum which means the liquid can flow through vacuum therefore the liquid will end up being recieved in the centrifugal pumps suction and because 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 air from the engine, therefore reducing the surroundings pressure 
build up created by blow due to combustion gases going past the piston rings in to the pan.