Can type oil filters are used mainly for filtering oil in engines. However, in mo-dern engines these filters are less popular. Previously important advantages such as good resistance to damage and easy replacement of used filters, practically with no risk of oil system contamination are not the priorty anymore, Presently the ecological aspects, especially easy filters utilization are more important In this respect, mmodern filter cartridges installed in dismountable casings are better. Appreance of can type oil filters is very similar, but the internal construction features for this group of filters must be optimally selected, to assure efficient operation in the engine oil system.

The high capacity engines often have oil systems with two types of filters. One full flow- all the oil pumped flows through while the second is built into the system in parallel and about 10% of oil flows through it. This oil after being purified goes back into the oil tank. The full-flow functions as a coarse filter while the by-pass filter is the fine filter in this system. In the oil system, centrifugal filters are often applied as by-pass filters, where contaminants are separated from the oil in the centrifulgal field of force.Filter are also used, made with a medium of special fabrics or filtering papers. The characteristic feature of by-pass filters with the medium is the amount of oil reduction during exploitation, which rusults from flow resistance increasing during the filter medium blocking. In some engines with full flow/by-pass oil system, the can filterswith two filtering cartridges (full-flow & by-pass) are applied. Such integrated filter systems take less space and its re-placement is much quicker. The oil flow is divided in such filters into the main flow directed into the engine and by-pass flow, which after proper purifications flows back into the oil tank.

Specially, the high capacity diesel engine use the combination type oil filter the oil from the oil pump is not split. All the oil from the pump is sent to a filter, where is passes through the full flow element and then by-pass elements provided. After being filtration, the oil flows in the same way as the full-flow type. Employs a special structure that provides internal oil pressure difference to allow both the full flow and by-pass elements to maintain their specified filtering ratio The by-pass element used, made with a medium of special fabrics or filter papers.

Generally, the anti-drain back valve have the form of a rubber membrane adjoi-ning the inner side of the can type filter cover. The membrane covers the holes where the contaminated oil gets through to the filter and protects from the back flow after the engine stops. The anti-drain back valve reduces the dry friction or mitigated solid friction time between working parts of the engine as protecting from the oil flow towards the pump and accelerates the oil flow into the working elements during the engine start, especially after a long break. The position the filter is screwed into the engine, conditions the valve application. If the filter works in the "cover up" position as shown in the picture below, the function of the valve is taken successfully by the gravitation. A valve is required when the filter in sore-wed in from the side or from the top of the engine body.

The by-pass valve is always installed in the oil system with full-flow filter (installed in series in the system). Usually it is built in the filter itself; however there are constructions where this valve is placed in the engine body. Regardless of the place where it is installed, its only function is to clear the oil flow when the flow resistance is too high and there is a risk of insufficient lubrication of working parts. It is considerde though that lubricating and cooling with contaminated oil is less damaging than the lack of lubrication which may read even to the engine seizing. There are basically two reasons why the oil flow resistance in the filter, opens the by-pass valve. First : high density which hppens in winter at low temperature. While starting the car after a long stop (i.e going to work in the morning), the cold and thick oil flows on the filter medium which makes the flow difficult. The pressure increase makes the by-pass valve open. The second reason for the by-pass valve opening is the filter medium wear. When the filter is excessively contaminated, its filter medium is chocked by contaminants. In this case it may hap-pen that the by-pass valve in continuously open. To avoid such situations, it is required to change filters and oil in accordance with the car manufacturer's recommendations.