GB1218023A - Improvements in or relating to rotodynamic pumps - Google Patents

Abstract

1,218,023. Centrifugal axial-flow pumps. WEIR PUMPS Ltd. July 24, 1968 [July 7, 1967], No.31309/67. Heading F1C. A rotodynamic pump for liquids comprises at least one impeller mounted within a housing, and an inducer to permit the pump to operate at a higher speed or with a lower suction head without producing any cavitation at the inlet to the impeller, and including a casing, an inducer shaft in the casing, screw blading mounted coaxially on the inducer shaft and extending at least to the impeller eye whereby the inducer discharges directly into the impeller, the tip diameter of the screw blading decreasing towards the impeller eye such that at the eye the tip diameter corresponds to the eye diameter. The first-stage impeller 3, Fig. 2, of a multi-stage centrifugal pump is preceded by an inducer 14 which prevents cavitation and comprises an axial-flow screw-bladed impeller secured to the pump shaft 8. The diameter of the impeller eye 4 is such as to provide optimum efficiency of the impeller 3, while the inlet diameter of the inducer 14 is larger to provide optimum suction performance of the inducer, the blade tip diameter of the inducer blading tapering between these sizes as shown. A shroud 18 having a correspondingly tapered conical surface 19 is secured to the inducer blading and is accommodated in an annular recess 20 in the pump casing. The shroud 18 and the recess 20 may be omitted, the surface 15 of the casing then being extended to form a conical surface enveloping the inducer blading. The inducer blading may be formed by an extension of some or all of the blades of the impeller 3. The pump impeller may be of axial-flow or mixed-flow type.