4-72 centrifugal fan can be used as general room ventilation factories and large buildings ventilation. Conveying air and other non-spontaneous combustion, harmless, non-corrosive gases for copper. B4-72 type fan can be used as ventilation of flammable vapors. F4-72 type fan made of stainless steel for conveying corrosive gases. From a front side of the motor, the Falun rotates clockwise, called D-blower to "there" means; counterclockwise rotation of the impeller, the "left". Centrifugal fan is based on the principle of potential energy is converted to kinetic energy, the use of high-speed rotating impeller accelerates the gas, and then slow down, change the flow of the kinetic energy into potential energy (pressure). In the single-stage centrifugal fan, the gas from entering the axial impeller, changing the gas flow through a radial impeller, diffuser and then enter. In the diffuser, the gas flow direction changes caused by deceleration, the deceleration effect converting kinetic energy into pressure energy. Pressure increased mainly in impeller, diffuser second place in the process. In a multi-stage centrifugal fan, and reflux into the next impeller allows airflow, resulting in higher pressure.