Abstract: A pump e.g. a screw pump, includes a main pumping element and a generally parallel auxiliary pumping element, and a pump housing, the main and auxiliary pumping elements interacting with each other and with an internal wall of an elongate pumping chamber of the housing as they relatively rotate to pump fluid from a first axial inlet end of the elongate chamber towards a second axial outlet end of the elongate chamber, and wherein the internal wall of the elongate pumping chamber includes at least one recess which extends along at least a substantial portion of the axial extent of the chamber between the inlet and outlet ends of the chamber, an adjacent pumping element being contactable with the chamber wall at discrete contact edges either side of the recess.

Abstract: An assembly includes first and second rotatable members which rotate about a common axis of rotation, the first member being connected to a first rotor and the second member being connected to a second rotor, the first and second rotors being concentrically arranged, the assembly further including a first stator including coils wound about a core, and a second stator including coils also wound about the core, the first rotor being rotatable in response to electrical current flowing in the coils of the first stator and the second rotor being rotatable about the axis in response to electrical current flowing in the coils of the second stator.