The external gear pumping principle

The external gear pumping principle uses two rotating gears which unmesh at the suction side of the gas station pump to create a vacuum which pulls fluid into the pump.  The spaces between the gear teeth transport the fluid along the outer perimeter of the housing to the discharge side, and then the gears re-mesh at the center to discharge the fluid.  The gears are supported by bearings on both sides, which allows high discharge pressure capabilities.