dry
　　A filter that separates impurities in the air through a dry filter element, such as a paper filter element. Air filters used in light vehicles (including sedans and microcars) are generally single-stage. Its shape has oblate circle or ellipse and flat type. The filter material is filter paper or nonwoven cloth. The end cover of the filter element has metal or polyurethane, and the shell material is metal or plastic. At rated air volume flow rate, the original filtration efficiency of the filter element should not be less than 99.5%. Heavy duty vehicles must have a majority of air filters due to poor working conditions. The first stage is a swirl prefilter (such as blade ring, swirl pipe, etc.), which is used to remove coarse particles and impurities with a filtration efficiency of more than 80%. The second stage is a microporous paper filter core (commonly referred to as the main filter core) with a filtration efficiency of more than 99.5%. The main filter element is followed by a safety filter element, which prevents dust from entering the engine when the main filter element is installed and replaced, or when the main filter element is accidentally damaged. The material of safe core is nonwovens mostly, also have use filter paper.