The function of air filter is to remove dust and sand particles from the air into carburetor, so as to reduce the wear of cylinder, piston and piston ring, prolong the service life of engine, and eliminate the intake noise. (Tests show that the wear of cylinder, piston and piston ring will increase 8 times, 3 times and 9 times without air filter in truck.) The installation of air filter increases the intake resistance and reduces the output power.

　　按濾清方式，汽油機用的空氣濾清器可分為三類：慣性式、過濾式和綜合式（前兩種的綜合）。根據濾芯方式，可分為干式、濕式和半濕式。干式空氣濾清器是在圓形筒中放人紙、布或合成纖維過濾材料；濕式空氣濾清器即油盤式空氣濾清器；半濕式空氣濾清器采用在發泡體聚氨醋中滲人油的方式。

　　According to the way of filtration, the air filters used in gasoline engines can be divided into three types: inertia type, filtration type and synthesis type (the first two kinds of synthesis). According to the way of filter element, it can be divided into dry type, wet type and semi-wet type. Dry air filter is to put human paper, cloth or synthetic fiber filter material in a circular cylinder; wet air filter is oil dish air filter; semi-wet air filter is to infiltrate human oil into foamed polyurethane vinegar.

　　綜合式空氣濾清器的工作情況是：發動機工作時空氣以極高的速度從蓋與殼之間的夾縫處流人，并沿殼的內壁向下流至油面處，再繞向上方。由于流動方向的急驟改變，較大的塵沙因慣性作用，即沖向機油面而被粘住留下；而較輕的塵沙，隨空氣一同進人浸機油的濾網，又被濾網粘附。這樣經過再次過濾，較干凈的空氣就從氣管流人化油器。

　　The working condition of the integrated air filter is that when the engine works, the air flows from the crack between the cover and the shell at a very high speed, and flows down to the oil surface along the inner wall of the shell, and then goes upward. Because of the sudden change of the flow direction, the larger dust is sticky because of inertia, i.e. rushing to the oil surface; while the lighter dust is sticky because it enters the oil-soaked filter with air. After re-filtration, cleaner air flows from the trachea to the carburetor.