To effectively inhibit contact of an impeller and a casing in a pump having recessed groove formed on the impeller and the casing.
A Wesco pump10 is provided with a roughly disk shape impeller 36 and a casing rotatably storing the impeller, and sucks fluid in the casing and delivers fluid out of the casing by rotation of the impeller 36. The recessed groove 36c compressing fluid in a clearance between the impeller 36 and the casing and generating force in a direction enlarging the clearance between the impeller 36 and the casing when the impeller rotates is formed on the impeller 36 or an inner surface of the casing. A clearance between a surface on which the recessed groove 36c is formed and a surface opposing to that surface gets larger as it goes from a center part of the impeller 36 toward an outer circumference part of the impeller 36.
MATSUBARA MAMORU
KATO NOBUHIRO
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