Roland J. Bishop

Tribological testing with hydraulic pumps: A review and critique

Hydraulic fluids serve two functions in the hydraulic system; to transfer energy and to lubricate the system. The energy transfer role is relatively well understood while lubrication assessment has been hindered by inability to adequately model hydraulic systems in general by small-scale pump prototypes or by bench testing. In general, most conventional bench tests do not adequately model wear which may accompany hydraulic fluid use in various hydraulic pump designs. Therefore, this has necessitated the use of hydraulic pumps as tribological test stands. The objectives of this paper are to: (1) review common failure modes of different types of hydraulic pumps, (2) provide an overview of the deficiencies of bench testing of hydraulic fluids, (3) review the tribological criterion for successful lubrication of vane, piston and gear pump testing, (4) review the most common pump tests reported to date, and (5) critique the quality of these tests relative to their ability to provide the required data.

Biodegradable Hydraulic Fluids: A Review

There is currently increasing interest in biodegradable hydraulic fluids. Such 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 olefin) and fire-resistant fluids such 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. From the literature available, an assessment of future directions in this ever-changing field will be provided.