Environmentally adapted lubricants, Part II. Hydraulic fluids

Current technologies relating to hydraulic fluids are mostly either mineral based, synthetic based, or water-based. Mineral oil based hydraulic fluids tend to be used for their excellent lubrication characteristics, economic viability, and so account for almost 90% of hydraulic fluids, while waterbased fluids tend to be employed in fire hazard applications. Synthetic hydraulic fluids possess superior properties to mineral oils, but their higher price limits their application to aerospace and special applications under severe conditions. In recent years, biodegradable hydraulic fluids, which are readily decomposed by micro-organisms, have come into focus due to the rise in environmental consciousness in European countries, particularly Sweden and Germany, and with this, vegetable-based fluids. In the present paper, the main categories of hydraulic fluids, including environmentally friendly fluids, are discussed in an overview of the state of technology in this area. Current governmental regulation, and the properties required of environmentally adapted fluids, and an appraisal of the current practices in various countries are also given. In an earlier paper*, the authors reviewed the key aspects of and requirements for environmentally adapted lubricants, namely, chemical composition, eco-toxicity, biodegradability, bio-accumulation, eco-labelling schemes, and life-cycle analysis. In the present paper, the main categories of hydraulic fluids, including environmentally friendly fluids, have been described. In Part I*, the authors reviewed the key aspects of and requirements for environmentally adapted lubricants.