A device usable as an impeller has a plurality of vanes rotating eccentrically about a shaft. Eccentric rotation is enabled by a cam mounted on the shaft. The vanes are received within slots in a rotor which surrounds the shaft and rotates about an axis coaxial with the shaft. The rotor rotates within a housing having a cylindrical surface facing the rotor. The surface is eccentric to the shaft. The vanes execute reciprocal motion upon rotation of the rotor. The vane motion is constrained so that the edges of the vanes remain proximate to the cylindrical surface during rotation.