Rotary Impeller Pumps

1,153,993. Centrifugal and axial-flow pumps. ROLLS-ROYCE Ltd, June 13, 1966 [June 16, 1965], No.25414/65. Heading F1C. The effective flow area at the inlet of a pump impeller having one or more helical blades 2, Fig. 1, is reduced by purposely creating a controlled region 7 of cavitation on the suction sides of the blades. This enables the pump to operate at high rotational speeds and low suction heads. The impeller hub may be conical or substantially cylindrical. In pumps having full admission to the impeller, Figs.4, 5 and 6 (not shown), the cavitation occurs over the whole span (i. e. from root to tip) of the leading edge 3 of each blade, whereas in pumps having a controlled inlet area, Fig. 7, the cavitation occurs over only the effective span of the blading (i.e. that part of the span not obturated by shutters 17). The shutters may be arranged to reduce the effective tip diameter or increase the effective root diameter of the blading, and are controlled by the pump delivery pressure through a piston 20 or through a bellows. The controlled cavitation is produced by making each leading edge of thin wedge-shaped form, with an included angle of 3 degrees or less, and by making the blade inlet angle A of small magnitude, i.e. about 0 to 8 degrees. The blade angle and pitch both increase from the leading edge 3 to the trailing edge 4 to cause the cavitation to be terminated within the impeller. The leading edge 3 may be curved, or may be straight and radial or forwardly or backwardly inclined.