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

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