Air filter: introduction
A device for removing particulate impurities from the air. When piston machines (internal combustion engines, reciprocating compressors, etc.) work, if the inhaled air contains dirt and other impurities, the wear of parts will be aggravated, so air filters must be installed.
The air filter consists of a filter element and a housing. The main requirements of the air filter are high filtration efficiency, low flow resistance, and long continuous use without maintenance.

Air filter: function
The engine will suck in a lot of air during operation. If the air is not filtered, the suspended dust in the air will be sucked into the cylinder, which will accelerate the wear of the piston set and cylinder. Large particles entering between the piston and the cylinder will cause serious cylinder pulling, which is particularly serious in a dry and sandy working environment. The air filter is installed in front of the carburetor or the intake pipe to filter out dust and sand particles in the air and ensure that sufficient and clean air enters the cylinder. Among the thousands of automobile parts, the air filter is a very inconspicuous component, because it is not directly related to the technical performance of the automobile, but in the actual use of the automobile, the air filter has a great impact on the service life of the automobile (especially the engine). On the one hand, if there is no filtering effect of the air filter, the engine will inhale a large amount of air containing dust and particles, causing serious wear of the engine cylinder; On the other hand, if maintenance is not given for a long time during use, the filter element of the air filter will be full of dust in the air, which will not only reduce the filtering capacity, but also hinder the air flow, causing the mixture to be too rich and the engine to work abnormally. Therefore, regular maintenance of the air filter is essential.

There are two types of air filter, paper type and oil bath type. In recent years, paper filters have been widely used because of their high filtering efficiency, light weight, low cost, convenient maintenance and other advantages. The filtering efficiency of the paper filter element is as high as 99.5% or more, and the filtering efficiency of the oil bath filter is 95-96% under normal conditions. At present, the paper air filter is widely used in cars, which is divided into dry type and wet type. As for the dry filter element, once it is immersed in oil or water, the filtering resistance will increase sharply. Therefore, it is forbidden to contact with water or oil during cleaning, or it must be replaced with a new one.

When the engine is running, the intake air is intermittent, which causes the air vibration in the air cleaner housing. If the air pressure fluctuates too much, the intake air of the engine will sometimes be affected. In addition, the intake noise will be increased at this time. In order to suppress the intake noise, the volume of the air filter housing can be increased, and some of them are also arranged with baffles to reduce resonance.

The filter element of air filter is divided into dry filter element and wet filter element. The dry filter element is made of filter paper or non-woven fabric. In order to increase the air passing area, most filter elements are processed into many small wrinkles. When the filter element is slightly polluted, it can be purged with compressed air. When the filter element is seriously polluted, it should be replaced with a new one in time.

The wet filter element is made of sponge like polyurethane materials. When it is installed, some engine oil should be dripped and kneaded evenly by hand to absorb foreign matters in the air. If the filter element is polluted, it can be cleaned with cleaning oil. If it is excessively polluted, it should also be replaced with a new filter element.

If the filter element is severely blocked, the air inlet resistance will increase and the engine power will decrease. At the same time, the increase of air resistance will also increase the amount of gasoline sucked in, resulting in too rich mixture ratio, which will deteriorate the engine running state, increase fuel consumption, and easily produce carbon deposits. At ordinary times, you should develop the habit of checking the air filter element frequently.