A constant-displacement fluid pump that uses sliding vanes to move fluid through the pump. An eccentrically mounted shaft is turned inside a circular housing that has an intake port on one side and an outlet port on the other. Flat vanes are free to slide back and forth through slots in the shaft as it turns.

As the shaft turns, the volume of the chamber connected to the intake port increases and pulls fluid into the pump. This fluid is carried around the inside of the pump until it reaches a point connected to the outlet port. At this point, the vanes sliding through the shaft decrease the volume of the chamber, and fluid is forced out of the pump. Vane-type pumps move a comparatively large volume of fluid, but produce a relatively low pressure and are used as fuel pumps and low-pressure air pumps.