At this point also in centrifugal because of high rpm since it is directly coupled to engine the pump 
creates partial vacuum this means the liquid can flow through vacuum hence the liquid will end up being 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 has the inlet hooked up to 1 or both valve covers, sometimes the valley pan. It SUCKS the air flow from the engine, thus reducing the surroundings pressure build-up Centrifugal Vacuum Pump created by blow due to combustion gases going at night piston rings in to the pan.
