Patent ID: 7284950

Claim:
An impeller that rotates for pressurizing fluid in a pump passage, the impeller comprising: an inner circumferential portion; and an outer circumferential portion that is arranged on a radially outer side of the inner circumferential portion, the outer circumferential portion having two axial end surfaces with respect to an axial direction of the outer circumferential portion, each of the two axial end surfaces having a plurality of vane grooves arranged in a rotative direction of the outer circumferential portion, wherein one of the inner circumferential portion and the outer circumferential portion has a plurality of wall surfaces that axially extend straight through the one of the inner circumferential portion and the outer circumferential portion, the plurality of wall surfaces defining a plurality of communication holes that axially penetrate the one of the inner circumferential portion and the outer circumferential portion, the plurality of communication holes are displaced radially from the plurality of vane grooves, the plurality of communication holes are arranged substantially along the rotative direction at nonuniform pitches, and wherein the plurality of vane grooves is arranged at substantially uniform pitches in the rotative direction.