Patent ID: 8282347

Claim:
An impeller, comprising: an impeller body in which an internal channel is formed, the internal channel extending inside the impeller body in a direction of a rotation axis spirally about the rotation axis to connect an inlet open in an end surface of the impeller body and an outlet open in a circumferential surface thereof; and at least one centrifugal vane provided in the impeller body, wherein the internal channel is formed to have a closed cross-section with a predetermined inner diameter inside the impeller body, an upstream end of the internal channel forms the inlet of the impeller body, and a downstream end of the internal channel forms the outlet of the impeller body, the internal channel has a predetermined passage diameter, an external channel is formed so as to continue to the outlet of the impeller body and go around the circumferential surface of the impeller body about the rotation axis, the external channel being defined by the centrifugal vane and being recessed inward in the radial direction from the circumferential surface of the impeller body, and the external channel has a reduced portion in which the channel width in the direction of the rotation axis reduces gradually as it goes downstream in a flow direction.