Blades manufactured using high quality materials: "220V Cooling Fan" impeller inside the air curtain is very long, so that a drum-shaped blades if the use of inferior materials, it can save a lot of costs, but not often long , deformation occurs, the entire blade is no longer in a straight line, but in the middle sag, after you can imagine, this sagging "220V Cooling Fan" turn up the fan in, what a high noise, and will lead to entire air curtain shock! Use a good quality motor: wind turbine is to rely on the electric motor to make it work, and if the motor is of poor quality, can not function properly or start weak, will not be tolerated, and if poor quality motor that will hear "220V Cooling Fan" motor "buzzing" sound issue, it is a kind of torture.