Patent attributes
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.
