"220V AC Cooling Fan" impeller structure, dimensions are in accordance with the rated air flow (CFM) designed, when the normal air flow (CFM) work, the gas enters the impeller in the direction of air flow blade inlet mounting angle of the same, the gas can be smoothly into the impeller, when "220V AC Cooling Fan" into the impeller gas flow is less than the rated flow of gas into the impeller radial velocity decreases, the gas flow into the opposite direction of the angular velocity of the impeller is reduced, and thus the blade inlet mounting angle is not consistent. "220V AC Cooling Fan" in the processing and leaves the installation process, the blade due to various reasons can not have exactly the same shape and the mounting angle.