To prevent sliding loss and wear and improve pump performance by preventing contact of an impeller and a pump casing when the impeller rotates.
An outside end part of grooves 36c, 36d formed on an impeller 36 is shifted to an anti-rotation direction side from an inside end part. A direction of viscous force drawing fluid into the grooves 36c, 36d when the impeller rotates is a direction from a center side toward an outer circumference side and coincides with a direction of centrifugal force acting on fluid in a clearance between the impeller 36 and pump casings 38, 40. Appropriate quantity of clearance is formed between the impeller 36 and the pump casing 38, 40 by generating lift on the impeller 36 in the pump casings 38, 40 by fluid sending out from a center side to an outer circumference side in the grooves 36c, 36d, to effectively prevent contact of the impeller 36 and the pump casings 38, 40.
MATSUBARA MAMORU
KATO NOBUHIRO
