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Many of the measures taken by automotive engine manufacturers to ensure compliance with emissions legislation have resulted in increased levels of soot particles entering the lubrication system of today's Diesel engines. Diesel lubricating oil condemnation limits are dependent upon a number of factors the primary of which, for an automotive Diesel lubricating oil, is the ability of the oil to continue to hold the soot particles in suspension at increasingly high concentration levels. However, once in suspension, high concentrations of soot particles can cause engine component wear, thus shortening engine life. For this reason, and in order to extend service intervals, it is desirable to remove these very small sub-micron pro-wear particles from the lubrication system.

It has been recognised for many years that the majority of failures in fluid power transmission components can be directly attributed to contamination. Furthermore, it has been observed that the size and concentration of these contaminant particles effects the wear rate of components. As a consequence of the reduction in acceptable dimensional tolerances of electro/hydraulic actuators, the acceptable cleanliness levels of fluid power oils have also reduced. Full-flow barrier media filtration alone can no longer cope with the necessary cleanliness levels for the smooth and consistent operation of electro/hydraulic actuators over their desired service life. By-pass filtration is the key to controlling oil cleanliness between services. Unfortunately, traditional barrier media filters of a suitably low micron rating tend to be excessively large to meet the desired service interval.

The ability of modern diesel engines to operate successfully with high soot loadings in their lube oils together with extended drain intervals has been achieved through the use of a range of techniques to condition the oil. Full flow filters, bypass centrifuges, heat exchangers and a range of sensors and complex monitoring systems have all been added to engines to ensure that the oil is delivered to the lubricated surfaces at the optimum temperature and cleanliness. Traditionally each of the devices in the lube oil circuit has been considered, designed and purchased separately from different suppliers. The current trend throughout the automotive industry to reduce the number of first tier suppliers can be seen as a good reason to combine the elements of the lube oil circuit into a single unit, however this is a short sighted approach.