| Abstract: | Hydraulic fluids based on rapeseed oil tend to oxidise and hydrolyse, especially at temperatures above 80°C. Long-term testing, with thirty-seven agricultural machines, of an Esso PFL hydraulic fluid was carried out to investigate the suitability of rapeseed oil based hydraulic fluids. The operating conditions, notably the kind of work being done and the thermal regime of the hydraulic fluids, were monitored for each machine. Oil refill quantities, repairs, and maintenance were also documented. Samples of the hydraulic fluids were analysed for technical characteristics and element content. Unused rapeseed oil based hydraulic fluids are more rapidly biodegradable and less toxic than mineral oil based hydraulic fluids. However, hydraulic fluids most often come into contact with the environment when they are used, either through accidents or through oil dripping from the hydraulic couplers. It was, therefore, the purpose of a second research project to investigate the environmental impact of rapeseed oil based hydraulic fluids in the course of use. Four rapeseed oil based hydraulic fluids were tested in the field on eight agricultural machines. The relevant operating conditions, such as thermal changes and pressure load, were monitored, and oil samples were analysed, as in the first project. Biodegradability was tested with the CEC L-33-A-94 test and the OECD 302 B test (the Zahn-Wellens method). Aquatic toxicity was determined by different test systems: waste water bacteria, photobacteria, plankton alga, garden cress, Daphnia, and Leuciscus. It was found that, generally, the candidate hydraulic fluids were suitable for use in the machines tested. It was also found that high biodegradability and low ecotoxicity were constant properties throughout the test period. Thus, the hydraulic fluids tested are suitable for application in agricultural machinery. |
