Right now also in centrifugal because of high rpm as it is directly coupled to electric motor the pump creates partial vacuum this means the liquid will certainly flow through vacuum hence the liquid will end up being recieved in the centrifugal pumps suction and because the impeller Centrifugal Vacuum Pump 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 surroundings from the engine, hence reducing the surroundings pressure build-up created by blow due to combustion gases going past the piston rings in to the pan.