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Three Filters

Three filters is a long-established synonym within the industry; it stands for three commonly used automotive accessories, namely oil filters, fuel filters and air filters. They are responsible for the filtration of media in the lubrication system, the combustion system and the engine intake system respectively.

  • The term “three filter” is synonymous with the need to overhaul or replace these three accessories when carrying out maintenance work on a car.
  • The life of a car depends to a large extent on the life of its heart – the engine. Overloading, driving at high speeds, poor starting and stopping habits can all lead to a reduction in engine performance and life expectancy. But it is dirt and pollution that are the most damaging to engine performance and life, and they are the number one engine killer. Filters are the only way to avoid dirt and contamination. 
  • So in a sense, as one of the 60 key parts of the car, the filter is the protector of the car engine. Since the introduction of the engine, people have come to realise from practice that the engine must have a filter, and if it is not fitted with a filter, the engine will wear out unusually fast. Especially modern high-speed engines wear more quickly. With the advancement of engine technology, the requirements for filters are becoming more and more demanding. 
  • The importance of the filter to engine performance and life is also increasingly recognised, many automotive engineers believe that one of the main reasons why modern engines have a long life is to have an effective filtration system.
  • The engine has air, oil and fuel filters of three kinds, generally known as “three filters”. They are responsible for the engine air intake system, lubrication system and fuel system in the medium of filtration.
  • The air filter is located in the engine intake system, which is composed of an assembly of one or several clean air filter components. Its main role is to filter out harmful impurities in the air that will enter the cylinder, in order to reduce the cylinder, piston, piston ring, valve and valve seat of early wear. There are two types of air filters, namely dry and wet.

Dry type of Three Filters

  • Dry air filter is through a dry filter element, (such as paper filter) will be the air of the impurities out of the filter. The air filter used in light vehicles (including cars and micro cars) is generally a single stage. It has a flat or oval shape and a flat plate type. The filter material is filter paper or non-woven fabric. The cartridge end caps are available in metal or polyurethane, and the housing material is metal or plastic. The original filtration efficiency of the filter element should be no less than 99.5% at the rated air volume flow rate. Heavy-duty vehicles have to have most of its air filters due to the harsh working environment. The first stage is a cyclonic pre-filter (such as vane ring, cyclonic tube, etc.), which is used to filter out coarse and large particles of impurities with a filtration efficiency of more than 80%. The second stage of fine filtration is a microporous paper filter element (generally called the main filter element), which has a filtration efficiency of more than 99.5%. After the main cartridge there is a safety cartridge, whose function is to prevent dust from entering the engine when the main cartridge is installed and replaced, or when the main cartridge is damaged by chance. The material of the safety cartridge is mostly non-woven fabric, but filter paper is also used.

Wet type of Three Filters

  1. Wet air filters include both oil-immersed and oil-bath types. The oil-impregnated type separates the air impurities by means of an oil-impregnated filter element, which is made of either wire fabric or foam. The oil bath type is the suction of dusty air into the oil pool and was removed most of the dust, and then in the air with oil mist upward flow through a wire wound cartridge for further filtration, oil droplets and stopped dust together back to the oil pool. Oil bath air filters are generally used in agricultural establishments and marine power.
  2. The oil filter is located in the engine lubrication system. It is upstream of the oil pump and downstream of the various parts of the engine that require lubrication. Its role is to filter out harmful impurities in the oil from the oil sump, to clean the oil supply crankshaft, connecting rod, camshaft, supercharger, piston rings and other movements, to play a lubrication, cooling, cleaning role, so as to extend the life of these parts, oil filters according to the structure of the interchangeable, spin-on, centrifugal; according to the arrangement in the system can be divided into full-flow, shunt type. The filtering materials used in oil filters are filter paper, felt, metal mesh, non-woven fabric and so on.
  • Before the eighties, the oil filter used in the national engine was mostly interchangeable. This structure of the filter is the filter element and other parts, such as springs, seals, etc. into a metal shell, through the pull rod will be the shell filter element and a metal filter seat connection fixed. The advantage is that it is cheap to use and only requires regular maintenance and replacement of the filter element. The disadvantage is that there are too many sealing points, and the cartridge may be left out of the maintenance and replacement parts, which may cause loopholes and make it difficult to replace.
  • Since the early eighties, the spin-on filter production line was introduced from Italy, the spin-on filter has been gradually used by domestic OEMs. This kind of filter is characterized by internal check valve, bypass valve, sealing point only one, the whole replacement, greatly improve the sealing, and easy to replace, its filter element materials are mostly imported filter paper, so high filtration efficiency, small flow resistance, long life. Now all domestic cars use this structure form of oil filter, the vast majority of micro cars, as well as large, medium and small buses, light, medium-sized trucks and some heavy trucks and agricultural vehicles have adopted the spin-on oil filter.
  • The centrifugal oil filter has a rotor set on a shaft and two nozzles with opposite spray directions. When the oil enters the rotor and comes out from the nozzles, the rotor rotates rapidly so that the oil inside the rotor is cleaned and the impurities in the oil are centrifugally thrown to the inner wall of the rotor and the oil from the nozzles flows back to the oil sump. The centrifugal oil filter is characterised by its stable performance, reliable structure and the absence of a filter element that needs to be replaced. Its life expectancy can be equal to that of the engine. Its shortcomings are its complex structure, high price and bulky weight, and the high technical requirements for the user.
  • Full-flow oil filters, such as the aforementioned interchangeable, spin-on, split-centrifugal, etc., filter all the oil entering the system. Split-flow filters filter only 5-10% of the oil supplied by the oil pump. The split-flow oil filters are all fine filters, which are generally used in conjunction with the full-flow type. Most of the small power engines only use full-flow filters, and the larger power diesel engines use full-flow plus split-flow filtering devices.
  • Fuel filters have diesel filters, gasoline filters and natural gas filters three types. Its role is to filter out harmful particles and water in the engine fuel gas system, to protect the fuel pump nozzle, cylinder liner, piston rings, etc., to reduce wear and tear, to avoid blockage. (Gasoline filters are carburettor type and EFI type, the use of carburettor gasoline engine, gasoline filter is located on the inlet side of the fuel pump, working pressure is small, generally using nylon shell, EFI engine gasoline filter is located on the outlet side of the fuel pump, working pressure is high, usually using metal shell. (The filter element of the petrol filter mostly uses filter paper, but also uses nylon cloth and polymer material.)
  • The structure of the diesel filter is roughly the same as that of the oil filter, and there are two types of replaceable and spin-on filters. However, its working pressure and oil temperature resistance requirements are much lower than those of oil filters, while its filtration efficiency requirements are much higher than those of oil filters. The filter element of diesel filter mostly uses filter paper, but also uses felt or polymer material. In addition to filtering the mechanical impurities in the diesel fuel, the diesel filter has an important function of filtering water. The presence of water is extremely harmful to the diesel oil supply system, rust, wear and tear, jamming and even deteriorate the combustion process of diesel. The main way to remove water from the diesel filter system is sedimentation. Either a precipitation chamber is set up in the lower part of the filter or a special precipitator is used. Both the lower sedimentation chamber of the filter and the special sedimentation device are equipped with a water release valve, which is opened when the water accumulates to a certain amount.

Gasoline filters have carburetor type and EFI type, using carburetor gasoline engine, gasoline filter is located on the inlet side of the pump, working pressure is small, generally using nylon shell, EFI type engine gasoline filter is located on the outlet side of the pump, working pressure is high, usually using metal shell. The filter element of the petrol filter mostly uses filter paper, but also uses nylon cloth and polymer material.


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