Oil purifier and oil filter play a role in puritying the lubricating oil of main engines and generators in marine vessels. The filters and oils of large trunk piston engines (TPE) after use were analyzed for determining the influence of lubricants on filterability. The filter clogged contained a large amount of carbon and CaSO{sub}4, and a small amount of CaCO{sub}3. Carbon and CaSO{sub}4 could be removed easily from the filter by solvents washing. On the other hand, CaCO{sub}3, which was formed by hydrolysis of overbased detergents, could not be removed easily probably because it was in a large needle-like crystal form. In order to wash off the clogging materials containing CaCO{sub}3, it was necessary to wash by "ultrasonic washing method".The CaCO{sub}3 contained in fresh overbased detergents exists in amorphous form. However, the amorphous CaCO{sub}3 is metastable thermodynamically and transforms to the needle4ike crystal, calcite, on heating in contact with water during use. The perioduntil the filter would be clogged depended upon the amounts of the particles that have equal to or larger than the mesh hole of the filter used. The small particles ranging from 3 to 4μm which were made from carbon and CaSO{sub}4 did not affect theclogging period. On the contrary, large particles from SiO{sub}2 and CaCO{sub}3 substantially shortened the clogging period.In conclusion, it was shown that the most important factor of lubricant filterability was the hydrolytic stability, which controlled the formation of needle-like CaCO{sub}3 crystale. The effects of the oxidation stability and the dispersion performance of lubricants were found to be negligible.
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