In a centrifugal pump, an enclosed-type impeller is provided with a plurality of auxiliary side vanes on either or both of the front and back faces of the impeller which project toward and conform with suitable running clearances to the walls of the casing adjacent the impeller. Annular members projecting axially from the sides of the impeller about the periphery thereof serve to limit circulation of working fluid into the spaces along the sides of the impeller. In one embodiment, the annular projection defines radially oriented passages or channels for transmitting fluid which is driven by the centrifugal action of the side vanes.
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