Today also in centrifugal due to high rpm since it is directly coupled to motor the pump creates partial vacuum this means the liquid will flow through vacuum hence the liquid will end up being recieved in the centrifugal pumps suction and because the impeller rotates the fluid will be displaced away forward with a particular energy.

A vacuum pump has the inlet hooked up to one or both valve covers, sometimes the valley pan. It SUCKS the surroundings from the engine, hence reducing the surroundings pressure build-up created by blow due to Centrifugal Vacuum Pump combustion gases going at night piston rings into the pan.