The filterability of lubricants in hydraulic operations is critical because fine filtration is necessary to prevent wear or seizure of machine components. Since water contamination is a common occurrence in hydraulic systems, fluids must maintain good filterability even in the presence of water. An evaluation of the filterability of prototype synthetic ester based hydraulic fluids was performed in order to determine how their properties differ from mineral oil based hydraulic fluids. The experimental procedure specified in ISO 13357-1:2002 Petroleum Products -^sDetermination of the Filterability of Lubricating Oils was used. Mineral oil and synthetic ester basestocks were found to have similar filterability properties. Multi-walled carbon nanotubes, methacrylate polymers, ashless and zinc-based antiwear additives were added to these basestocks. The results indicate that synthetic ester blends containing additives have similar filterability to mineral oils containing the same additive system. Commercial petroleum-based lubricants were evaluated for comparison purposes. The synthetic ester formulations evaluated in this study exhibited filterability properties that were at least equivalent to mineral oil based hydraulic fluids and commercial lubricants.
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