Abstract: A centrifugal fan includes a scroll casing consisting of first and second flat base walls, a circumferential side wall. An air inlet is formed on the first base wall, an exhaust port is formed on the side wall. A backflow prevention mechanism is arranged in the airflow path to prevent backflow from the exhaust port during fan halting. The mechanism has a flap that is rotatably supported by the first base wall and its 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 the motor is horizontal. The flap is inserted into a slit from the outside and is held by a stopper plate. A protrusion, which contacts with the rim of the flap when the flap shuts the airflow path, is formed inside the walls.

Abstract: In a centrifugal fan including a casing, a rotatable impeller disposed in the casing, a motor for driving the impeller, a control board for controlling the motor, and an ejection port for cooling air, a dust proof projection is formed to the casing to prevent invasion of dusts from the ejection port to the motor and the control board. With this simple arrangement, invasion of dusts to a coil portion and a control board of the motor can be reduced while suppressing a manufacturing cost. In this case, when the dust proof projection is disposed to a gap between the inner peripheral surface of a side wall of the casing and the outer peripheral surface of the impeller along the outer peripheral surface of the impeller in an arc-shape, a dust proof effect can be more improved.

Abstract: A centrifugal fan includes a scroll casing consisting of first and second flat base walls, a circumferential side wall. An air inlet is formed on the first base wall, an exhaust port is formed on the side wall. A backflow prevention mechanism is arranged in the airflow path to prevent backflow from the exhaust port during fan halting. The mechanism has a flap that is rotatably supported by the first base wall and its 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 the motor is horizontal. The flap is inserted into a slit from the outside and is held by a stopper plate. A protrusion, which contacts with the rim of the flap when the flap shuts the airflow path, is formed inside the walls.

Abstract: An impeller of a centrifugal fan having a casing and a multi-blade impeller rotatably supported by a blade holding base in the casing, wherein when the impeller is rotated air is sucked from an air suction port formed on one side wall of the casing, and a centrifugal force is applied on the air, so that air of high pressure is taken out through an outlet formed on a portion of an outer peripheral surface of the casing. An inner peripheral surface of the impeller is formed of a conical surface having a large diameter at the suction port and a small diameter at the blade holding base. The small diameter at the blade holding base is in the range of 70 to 90% of the large diameter at the suction port. The diameter of the inner peripheral surface of the impeller is reduced linearly from a portion at the suction side to a portion at the blade holding base side.

Abstract: An impeller of a centrifugal fan having a casing and a multi-blade impeller rotatably supported by a blade holding base in said casing, wherein when said impeller is rotated air is sucked from an air suction port formed on one side wall of said casing, and a centrifugal force is applied on said air, so that air of high pressure is taken out through an outlet formed on a portion of an outer peripheral surface of said casing. An inner peripheral surface of the impeller is formed of a conical surface having a large diameter at the suction port and a small diameter at the blade holding base. The small diameter at the blade holding base is in the range of 70 to 90% of the large diameter at the suction port. The diameter of the inner peripheral surface of the impeller is reduced linearly from a portion at the suction side to a portion at the blade holding base side.