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