The wind pressure coefficient of a diagonal flow fan is higher than that of an axial flow fan, and the flow coefficient is larger than that of a centrifugal fan. It is used in situations where both wind pressure and flow rate are "neither too large nor too small". It fills the gap between axial flow fans and centrifugal fans. Simultaneously possessing the characteristics of simple and convenient installation. The mixed flow fan combines the characteristics of axial and centrifugal fans, and its appearance looks more like a traditional axial fan. The casing may have an open inlet, but more commonly, it has a right angled curved shape that allows the motor to be placed outside the pipeline. The excretory shell slowly expands to slow down the velocity of air or gas flow and convert kinetic energy into useful static pressure. The SWF (B) series low-noise energy-saving mixed flow fan is a new type of fan that is between axial and centrifugal fans. It has the characteristics of high pressure of centrifugal fans, high flow rate of axial fans, high efficiency, good energy saving, low noise, and easy installation. The fan has a novel design, compact structure, small size, light weight, easy installation, with a speed of less than 2000r/min and a noise level of less than 75dB (A). When the fan is connected to the pipeline and installed in the air conditioning box, the noise level is less than 70dB (A). Low pressure centrifugal fans are widely used for ventilation and dust removal in industrial and civil buildings.