Now also in centrifugal due to high rpm since it is directly coupled to electric motor the pump creates partial vacuum which means the liquid will certainly flow through vacuum hence the liquid will become recieved at the centrifugal pumps suction and because the impeller rotates the liquid will be displaced away forward with a particular energy.
A vacuum pump has the inlet hooked up to 1 or both valve covers, sometimes the valley pan. It SUCKS the atmosphere from the engine, hence reducing the atmosphere pressure Centrifugal Vacuum Pump build-up created by blow because of combustion 
gases going at night piston rings into the pan.