Oil filter

An oil filter removes particles from oil, which is mostly used in closed circuits. The best known design consists of a housing, generally deep-drawn from metal, and the actual filter, consisting of a nonwoven fabric or a woven fabric.

As an oil filter creates a pressure drop, the oil must be forced by a pump through the filter. Therefore, the filter is located in the cycle, usually just behind the pump. This is known as a so-called " main stream filter ". In the suction line before the pump is located may require a coarse screen, which is to protect the pump. Example, this is the usual arrangement in automotive engines and aircraft engines. In aircraft engines, a coarse filter (strainer) for protection against dirt built is still before each lubrication point (possibly even chips from the production). An installation of the filter in the return line, where the pressure is the lowest, and thus the housing of the filter can be assembled as easily and cheaply as possible, in principle, also possible. It depends on the application and the security principals. The oil filter ( main filter ), are provided for safety with a bypass valve ( bypass valve ) to maintain the operation with unfiltered oil at a filter blockage and to avoid bursting of the filter. For aircraft engines, the pressure drop across the oil filter is continuously monitored and then determines the maintenance required for technical exchange.

• 3.1 Protection function filtering
• 3.2 wear protective filtering

Filter in internal combustion engines

Combustion engines are lubricated with oil. The heat from the combustion can also share the oil burn. For the lubrication of the machine is maintained, burned in the oil filter shares of the oil, metal dust and other dirt are filtered out ( eg, carbon black ). In the motor vehicle, the filter is replaced periodically, typically every year or every 10,000 to 30,000 kilometers by by the manufacturer at the cars. For aircraft engines, the housing of the filter is cut open and examined whether the chips have accumulated. Chips are a sign of dangerous wear.

Bypass filter

The bypass filter is arranged parallel to the full flow oil filter. Characterized flows only a portion of the oil flow through the oil filter (5 % - 10 %) and the pore size can be reduced so much that the smallest impurities can be filtered out. The effectiveness of side stream filters in view of the extension of the oil service life is, depending on the application, controversial.

Microfilter

One in the automotive field occasionally upgraded version is the micro filter in sidestream arrangement. In this case, a certain part of the oil is continuously pressed directly from an oil pan or the like through a second filter, without passing through the motor. Through the bypass filter finer particle sizes can still up to 0.1 micron are filtered out, whereas the main flow filter have channel widths of 5-10 microns. The main advantage is that condensation water is removed from the oil. There are also concepts that work exclusively with a filter in the bypass flow. The use of biogenic oils is for this reasons of environmental protection increasingly sought. Since the oil is but not only burdened by pollution, but is aging due to oxidation and the stresses occurring in the engine (heat, shear forces, etc. ) and especially the additives have a limited lifespan, a prolonging effect on the oil change intervals is controversial.

Centrifugal oil filter

Another concept for oil filtration in the bypass flow is the centrifugation. This principle is currently mainly in trucks being used increasingly. Here, the oil pressure is used to drive similar to the dishwasher or lawn sprinkler a Segnersches Fluidrad ( after Johann Andreas Segner of ). As the oil passes through the filter, it is subjected to high centrifugal forces, which means that soot and other small contaminant particles whose density is greater than that of the oil, are separated. With centrifugal oil filters can also be microscopic air bubbles to eliminate specifically from the oil, which could affect the lubricating properties very disadvantageous else: They accumulate due to their lower weight in the center, where they combine and burst.

Filter in oil heaters

In oil heating oil filters are also used, which must be replaced at service intervals. Various types of filters are available (paper, felt or plastic filter).

Filters in hydraulic systems

Oil filters are also used in all hydraulic systems. We distinguish between two different reasons of filtering:

Protection function filtering

The filtering aims only sure to remove stubborn grime that would interfere with the operation of the machine by jamming or clogging. The filters used are pretty gross in general. Mostly surface filters are used such as wire screens. These filters are used in simple and little-used hydraulic systems, such as car jacks and car lifts.

Wear protective filtering

To wear protection is very finely filtered to remove as many particles that can cause abrasion. It depth filters are almost exclusively used, remove the foreign body from 1/1000 mm size. These filters are used for expensive and complex hydraulic systems: excavators, injection molding machines, machine tools, presses, construction machinery, tunnel boring machines, agricultural machines, etc.