Oil filter is always replaced along with oil and it is a part that we do not really think about whereas it is very important. As it usually the case, such trifle like this part, might play quite an essential role. That is why it is worth to learn about its structure and principles of operation.
Engine oil is located in oil sump which is its reservoir. After it is sucked in, it reaches the first filter. This filter is a strainer that separates dirty oil from larger and more harmful impurities. Dirty oil gets to oil filter and after passing through this filter, oil must be clean to fulfill its function. Oil filter is designed to get rid of impurities that are 1/50 millimeter-large. If this cannot be done, even the smallest particles of sand can destroy the engine. Of course this would not happen immediately, but such process repeated several times, significantly affects life of the engine. This does not only refer to sand, but also to soft and harmless impurities like synthetic fibers or plastics.
The most common type of oil filter is a small metal can, hence the name can filter. Inside there is a paper filter cartridge, resistant to oil dissolving, but at the same time permeable and letting oil through its surface. In general, its looks like a harmonica-shaped air filter, and works in a quite similar way. Inside the cartridge there is an overpressure valve. What does it do?
Dirty oil enters the filter and then flows from the filter to the engine. Now the oil is forced into filter through small holes in its cover, and after passing through the filtering cartridge, filtered oil flows into the engine through large hole in its center, under high pressure of about 5 bar. It is not a problem for the filtering cartridge if oil has proper viscosity, is warm and the cartridge itself is clean. However, once the cartridge is already dirty or oil remains cold and dense, it is not always able to pass through the paper cartridge. If this issue remained unresolved, cold engine would sometimes not get the right amount of oil and the filtering cartridge could break ? this sometimes happens in filters of poor quality. The solution is a valve that, at high pressure, opens flow of unfiltered oil. Even when this is rare, this fact can make you aware of the importance of proper quality of filters, their choice with regard to properties of overpressure valve, as well as appropriate viscosity of oil. In many engines, the filter housings are installed in the engine permanently and only the filter cartridge is replaced – in a sense, such solution eliminates the problem of choosing right oil filter and its parameters.