Centrifugal fan is a driven fluid machine, which relies on input mechanical energy to increase gas pressure and discharge the gas. Centrifugal fans are widely used for ventilation, dust exhaust and cooling in factories, mines, tunnels, cooling towers , vehicles, ships and buildings; centrifugal fans are composed of casing, main shaft, impeller, bearing transmission mechanism and motor. Case: It is made of steel plate and is sturdy and reliable. It can be divided into integral type and semi-open type. The semi-open type is convenient for maintenance. Impeller: consists of blades, curved front disc and flat back disc. Rotor: Static and dynamic balance should be done to ensure smooth rotation and good performance. Transmission part: It consists of main shaft, bearing box, rolling bearing and belt pulley (or coupling ).