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There is an ongoing interest in biodegradable hydraulic fluids. Biodegradable fluids are often considered to include only vegetable oils, polyol esters and diester base stocks. However, other fluid base stocks including highly refined mineral oils, poly(alpha olefins) and fire-resistant fluids such as water-glycol hydraulic fluids are also biodegradable fluid alternatives. This paper will provide an overview of the international literature on biodegradable fluids, various international testing protocol, fluid base stocks, effect of oxidative stability, material compatibility and pump performance.

It is difficult, if not impossible; to select any single test that will model the expected performance of any hydraulic fluid in a wide range of hydraulic pumps made by many different manufacturers. Increasing pressures often encountered in new hydraulic pump applications compounds this problem. However, some basic assessment of hydraulic fluid performance is necessary for numerous reasons such as: developing an appropriate fluid purchase policy, international standard development, fluid classification and others. Since the now-classic standard tests such as: ASTM D-2882, DIN 51389 and others are simply inadequate for this task and also since the manufacturer, Eaton Inc., no longer manufactures these pumps, it has been necessary to develop an alternative testing strategy [1, 2 and 3]. The Bosch-Rexroth Corporation has developed a high-pressure piston pump test that has been an excellent predictor of hydraulic fluid performance for many years.

Fire is a serious hazard in many industrial applications requiring the use of approved fire-resistant hydraulic fluids. A subgroup of these applications are facilities for the processing of food which in addition require hydraulic fluids and other lubricants used in these facilities to adhere to specifications set down by the United States Food and Drug Administration (FDA) and enforced by the Food Safety Inspection Service (FSIS) branch of the U.S. Department of Agriculture (USDA). The objective of this paper is to provide an overview of the current requirements in the United States for food-grade fire-resistant hydraulic fluids. Water glycol type hydraulic fluids; currently the only commercial food-grade fire resistant hydraulic fluids available, are compared in properties and performance to standard water glycol hydraulic fluids used in steel making and die casting facilities.

There are numerous fluid-related performance concerns when hydraulic fluids are being qualified for use. These concerns are especially important when non-mineral oil derived hydraulic fluids are being qualified for use in unusual and critical applications. In this paper, a number of performance-related fluid deficiencies that may be encountered in use will be described.

In many situations, the root cause of a particular failure may be determined based on the observation of a single part, or perhaps a photograph, taken from the failed system. However, when failure analysis is conducted on the complete component, a different result often emerges. Such is the case described here for a piston pump that was operating on an anhydrous poly(alkylene glycol) - PAG at high pressure. Initial observation suggested the fluid was the root cause of the failure. However, when failure analysis was properly applied, it was learned that the root cause of the failure was due to mechanical failure caused by the motor-to-pump coupling. This analysis procedure is presented as a case history in this report.