4-72 centrifugal fan is a kind of highly effective energy saving one, its wing leaf blade, the curve impeller and awl arc current collector make the fan have a fine lift-drag ratio. In 4-72 fan, No. 2.8-6A fan is mainly composes of impeller, cabinet, inlet and motor. No. 8-10C,D fan is composed of transmission, belt pulley and shaft coupling. The rotation of 4-72 fan is divided into clockwise and the counterclockwise, facing squarely from one side of the motor, I the impeller revolves clockwise, the fan is called a clockwise rotation one. If counterclockwise, it is called a counterclockwise one, expressed by “left”. The rotation of the fan must indicate when ordering. The outlet position of 4-72 fan is indicated by outlet of the cabinet. No.2.8 6A was made into one kind of pattern when leaving the plant, the user may install it according to the outlet position, no indication when ordering. No.2.8 outlet position may adjust from 0°to 225°, gap 45°. No. 3.2 6A outlet position may adjust from 0°to 225°, gap 22.5°. No. 8 12 0° 225°, gap 45°, must indicate when ordering. No. 16 20 has 3 kinds of fixed angles: 0°, 90°, 180°, cannot adjust when installs, must indicate ordering. The transmission of 4-72 fan has A, B, C, D 4 kinds, A: impeller and motor straightly jointed. B: leather belt, the belt pulley between two bearings. C: leather belt, the belt pulley in the flank bracket outside the bearing. D: shaft coupling transmission for impeller and motor. No. 2.8 5 uses A type; No.6 uses A, C and D3 type; No. 8 12 uses C and D2 type. Suitable situation: 4-72 centrifugal fan suits in ventilation, deliver or exhaust in all kinds of civil and industry architectures.