Patent ID: 7329089

Claim:
A centrifugal fan comprising: a scroll casing that has first and second flat base walls, a circumferential side wall covering the circumferences of said base walls, an air inlet that is opened in an axial direction being formed on a center portion of said first base wall and an exhaust port that is opened in a circumferential direction being formed on one portion of said circumferential side wall; a motor that is attached to a center portion of said second base wall at an inside of said casing so that a rotating shaft of the motor is perpendicular to said second base wall; an impeller that is fixed to said rotating shaft, the impeller having many blades along an outer region thereof; and a backflow prevention mechanism that prevents backflow from said exhaust port during fan halting by shutting an airflow path to said exhaust port, wherein said backflow prevention mechanism has a flat-shaped flap that is rotatably supported by said first base wall so that one side touching to said first base wall is a rotation axis, and the rotation axis is inclined with respect to the vertical direction so that the flap shuts the airflow path under its own weight in a horizontal-use position where the rotating shaft of said motor is horizontal, and a slope member, onto which the lower edge of said flap runs when said flap opens due to a push by the discharged airflow so that said flap is slightly displaced upward in the direction of the rotation axis, is formed inside the walls that form the airflow path at a side of the rotation axis under said flap in the horizontal-use position.