MC97 Johnson impeller - Glycerine Spline Drive **About Impellers** A vacuum is created as the flexible impeller vanes straighten upon leaving the cam, drawing liquid into the pump. The rotating impeller carries liquid from the inlet to the outlet port. As a consequence of their design, flexible impeller pumps can pass fairly large solids. When the flexible impeller vanes regain contact with the cam, they bend and the liquid is discharged from the pump in a uniform flow. Liquids can be pumped in the opposite direction by reversing the rotation of the pump.