During the past three decades, there have been notable advances in the design of pumps. In a number of projects, the designers of process plants had, during optimization of their layouts, established a requirement for pumps that outwits the standard ranges available from the majority of pump manufacturers. A considerable degree of technical expertise, backed by prototype development, is required if the benefits of high-speed operation are not to be offset by unreliability.The flow within a

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... ifugal impeller is qualitatively unlike thatin all other turbomachinery. The flow is very mixed, with strong influence of the viscous shear at the walls.This paper describes how the rotational motion ahead of theimpeller, created by partial bleeding from delivery side to the suction using suitable arrangements of nozzle units, has allowed the adoption of increased operating discharge pressures without embarrassingly high net positive suction head (NPSH) requirements.