Patent ID: 8419360

Claim:
A multi-blade centrifugal fan, comprising a fan casing having a pair of opposed side plates and a multi-blade centrifugal impeller, wherein the fan casing is provided with a pair of opposed bellmouths each forming an air intake and an air outlet, and has a tongue portion, wherein the multi-blade centrifugal impeller is arranged inside the fan casing and has a number of annularly arranged blades, the multi-blade centrifugal impeller draws in air through an intake which faces each of the bellmouths and blows the air out in the centrifugal direction through the blades, wherein each end portion of the impeller in the axial direction is provided with a retainer ring for retaining the blades, and a cylindrical body is integrally provided in such a manner as to extend from an outer end of each retainer ring, wherein each of the bellmouths bulges outward from a respective one of the side plates of the fan casing and an annular space is formed inside each of the bellmouths, and wherein a longitudinal cross section of each cylindrical body extends in a circular arc form from a longitudinal cross section of each retainer ring such that a diameter of an outer peripheral surface of each cylindrical body gradually increases toward each of the bellmouths.