There are two types of air filters, namely dry and wet. Dry air filters are filters that separate impurities in the air through a dry filter element (such as a paper filter element). The air filters used in light vehicles (including cars and mini cars) are generally single-stage. Its shape is oblate or elliptical and flat. The filter material is filter paper or non-woven fabric.
The filter element end cap is metal or polyurethane, and the shell material is metal or plastic. Under the specified air volume flow, the original filtration efficiency of the filter element should not be less than 99.5%. Heavy vehicles must have a large air filter because of the harsh working environment. The first stage is a cyclone pre-filter (such as a blade ring, a cyclone tube, etc.), which is used to filter out coarse particle impurities.
The filtration efficiency is above 80%, and the second stage fine filter is a microporous paper filter element (generally called a main filter element), and its filtration efficiency is above 99.5%. There is also a safety filter after the main filter, which is used to prevent dust from entering the engine when installing and replacing the main filter or when the main filter is accidentally damaged. The material of the safety filter is mostly non-woven fabric, and there are also filter paper.
Wet air filters include oil-immersed and oil-bath types. The oil-immersed type separates impurities in the air through an oil-immersed filter element. The filter element materials include metal wire fabric and foaming materials. The oil-bath type guides the dust-laden air sucked in into the oil pool to remove most of the dust.