ABSTRACT
A great many rotary pump mechanisms have been developed. All, however, function in the same basic manner. A series of fixed or controlled displacement volumes move continually and at essentially constant speed within the pump. Movement of the displacement volumes is either rotary or translational, but always produced by rotary motion. The essential feature of rotary pumps is movement of the displacement volumes from suction to discharge, thus eliminating the need for suction and discharge valves. Rotary pumps are positive displacement devices. Thus, for a given speed and viscosity, they produce a nearly constant flow, the variation depending upon the differential pressure across the pumps. As viscosity increases, internal leakage (slip) decreases, thus raising the capacity delivered. At the same time, friction power increases, thus raising the absorbed power. The principle governing rotary pump interaction with the system is the same as that for centrifugal pumps: the operating capacity is given by the intersection of the pump and system head characteristics.
