At this point also in centrifugal due to high rpm as it is directly coupled to engine 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 specific energy.
A vacuum pump has the inlet hooked up to 1 or both valve Centrifugal Vacuum Pump covers, sometimes the valley pan. It SUCKS the surroundings from the engine, therefore reducing the surroundings pressure build up created by blow due to combustion gases going past the piston rings into the pan.