Compatibility and Filterability of Hydraulic Fluids

This paper examines the compatibility and filterability characteristics of mineral oil and bio-based hydraulic fluids. Due to advantages in renewability and environmental acceptability, bio-sourced, biodegradable hydraulic fluids are increasingly used in fluid power applications. Conversion from mineral oil based fluids to biodegradable fluids can be expensive because hydraulic systems often must be drained and flushed several times during the conversion process. The goal of this research is to investigate the use of the ISO 13357:1 wet filterability procedure as a method for determining the compatibility of hydraulic fluids. Mineral oil, vegetable oil and synthetic ester based hydraulic fluids mixtures have been evaluated. An additive combination that is known to have marginal compatibility has been evaluated under conditions of varying temperature, duration, and concentration. The results reveal that the ISO 13357:1 wet filterability procedure is a robust method for evaluating hydraulic fluid compatibility. Based upon these findings, an ASTM standard practice for evaluating the compatibility of mixtures of hydraulic fluids has been drafted and submitted to ASTM Subcommittee D02 for ballot consideration. Included in the method is a flow chart to aid in interpretation of the test results and hydraulic system conversion.