During the working process of the range hood, the impeller rotates at high speed in the volute, and negative pressure is formed in the volute. In the rising process, the oil fume is sucked into the machine by strong airflow and cooled and separated by the impeller. After a long time, some oil stains will accumulate on the impeller, which will increase the weight of the impeller, the speed will become slower and slower, and the suction will become smaller and smaller!