Negative pressure fan is a kind of equipment with very good ventilation and cooling effect. It mainly discharges indoor heat and odor through negative pressure ventilation, and outdoor fresh air flows in for ventilation. The air exchange rate is as high as 99%, which can be used in agriculture, animal husbandry, industry and other places. Positive pressure fan drives the change and flow of airflow with high pressure, and has a thrust, which can effectively prevent external dust from entering the interior and maintain a high degree of cleanliness, especially in clean rooms, pumps and valves.