What happens when the gasoline filter is installed backwards? -Talk about the structure and filtering principle of gasoline filter.

As we all know, cars have "three filters", namely, oil filter, air filter and gasoline filter. The oil filter and air filter need to be replaced every time they are maintained. Everyone is familiar with it, but the existence of the gasoline filter is so low that many people don't even know where it is installed. Today, let's talk about what this gasoline filter is for, when it should be replaced, and what to pay attention to when replacing it.

Gasoline filter is commonly known as "gasoline filter element". Its main function is to filter the mechanical impurities, colloid and moisture in gasoline, provide clean gasoline for the engine, and also store a small amount of gasoline to avoid the interruption of oil supply when the automobile uses a lot of oil for a short time. In addition, it can also buffer the pulsation of gasoline pressure and stabilize the pressure of fuel system. Gasoline filters are divided into built-in and external types. Built-in gasoline box installed in front of the oil inlet of gasoline pump, generally integrated with gasoline pump; The external type is generally installed under the automobile chassis, but the external type generally has a filter screen in front of the oil inlet of the gasoline pump, which can filter relatively large particulate impurities, which is essentially secondary filtration.

The structure of gasoline filter is very simple, that is, a metal shell wraps a filter element. The metal shell is generally made of aluminum, which is light in weight and has good anti-corrosion effect. An oil inlet, an oil outlet and an oil return port are machined on it. The filter element is generally folded with microporous filter paper, installed on a chrysanthemum-shaped stainless steel bracket, and sealed with resin glue at both ends. It is also made of microporous ceramics or cotton yarn. Its working principle is also very simple. Gasoline enters from the oil inlet, and then penetrates into the inner surface from the outer surface of the filter paper. In this process, impurities and colloid with larger particles are left on the outer surface of the filter paper, and the filtered clean gasoline flows into the oil outlet from the inner surface of the filter element and is sent to the engine for combustion. For the gasoline filter element with oil return function, there is also a pressure limiting valve inside. When the oil supply pressure exceeds the pressure specified by the system, the pressure limiting valve opens and the excess fuel returns to the fuel tank.

The gasoline filter has several important parameters, one is the filtering accuracy, which is determined by the size of the filter paper micropores. Particles with a diameter greater than 0.0 1mm are generally not allowed to pass through the filter paper, and the filtration accuracy of some models is higher, reaching 0.005 mm Generally, the filtration accuracy of direct injection in the cylinder is higher than that of multi-point injection. The second is the dust capacity, which determines the service life of the gasoline filter. The higher the dust holding capacity, the longer the service life. The third is the bearing capacity. The ordinary multi-point injection gasoline filter can withstand the pressure of 2~4bar, and the in-cylinder direct injection gasoline filter can withstand the pressure of 4~6bar. They are not interchangeable. In addition, there are flow, original resistance and filtration efficiency, which have little to do with our practical application.

Some people say that the gasoline we added at the gas station looks clean. Why filter? What happens without filtering? What effect does it have on the engine? In fact, gasoline looks clean, but there are many dust particles, mechanical impurities, colloids and moisture that we can't see with our naked eyes. According to the testing data of refineries, the gasoline sold in China contains an average of 35 grams of impurities per ton, and each milliliter of gasoline contains more than 1500 mechanical particles with a diameter greater than 0.0 15 mm. If these impurities enter the fuel injection system, it will seriously damage the injector and aggravate the cylinder wear.

The injector of EFI system is the most precise component in the fuel supply system, and its interior is a precision coupling with a small gap, generally only a few microns. Especially in the direct injection engine, its injector coupling has higher accuracy, higher injection pressure and faster gasoline flow rate. If unfiltered gasoline enters the fuel injector, impurities in the gasoline will wear or block the fuel injector, making it impossible for the fuel injector to inject fuel normally. For example, impurities will block the injector, resulting in too little fuel injection and the engine speed cannot be increased; If the injector coupler is scratched, it will cause the injector to leak oil and drip oil, the engine fuel consumption will increase, and the exhaust pipe will emit black smoke.

In addition, large impurities in gasoline will also enter between the piston and the cylinder wall and play the role of abrasive, further aggravating the wear of the cylinder; In addition, the gum in gasoline is nonflammable, which is an important source of carbon deposition in the engine. Inferior gasoline contains more gum, and the carbon deposition in the engine will be more serious. Therefore, this unfiltered unclean gasoline cannot meet the normal working requirements of the engine, and the gasoline must be filtered before entering the engine.

So how often is it appropriate to change the gasoline filter? This is mainly related to fuel quality. The higher the quality of gasoline, the purer it is, and the longer the service life of gasoline filter. There is also the dust capacity of the gasoline filter element, which is also a very important factor. Obviously, the greater the dust holding capacity, the longer the service time of the gasoline filter element. Generally speaking, the external filter is replaced once every 20,000 kilometers, and the internal filter is replaced once every 60,000 kilometers. Of course, this is not an absolute time limit, and it can fluctuate according to the actual situation. When the car accelerates slowly or suddenly, it is first suspected that the gasoline filter is blocked. In addition, after a car that has used pure gasoline for a long time is replaced by ethanol gasoline, the colloid and dirt deposited in the fuel tank will be cleaned because of its strong cleaning effect, which is easy to block the gasoline filter.

The replacement of the gasoline filter element is relatively simple. For external type, it is generally installed under the chassis. Just lift the car, remove the connecting oil pipe and the fixing screw, and it can be replaced. For the built-in type, it is installed in the gasoline tank and combined with the gasoline pump, so it is difficult to replace it alone, and it is often replaced with the gasoline pump. It should be noted that before replacing the gasoline filter, the fuel system should be decompressed to avoid gasoline splashing around when the oil pipe is disconnected; There is also the need to replace the car in a cold state to prevent gasoline from splashing on the hot exhaust pipe.

Another thing to note is that the external gasoline filter element is directional, and there are generally signs of "in", "out" or "→" on it. Don't make a mistake. If the installation is wrong, the oil inlet and the oil outlet are connected reversely, gasoline will enter from the oil outlet and push the filter paper out from the inside, resulting in damage to the gasoline filter element and loss of filtering effect. In this case, short-term use is generally no problem, but long-term use is likely to cause problems such as slow acceleration of the car and wear and blockage of the injector.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.