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Because of on-board fire problems during World War II, the us Navy initiated a program to develop hydraulic fluids that were more fire-resistant than the mineral oils that were in use at that time. Water-glycol hydraulic fluids were subsequently developed and first commercialized in 1947 which offered vastly improved fire resistance relative to mineral oils. Since 1947, in addition to formulation changes, there is significantly greater understanding of the impact of these changes on pump wear performance. This paper will present a selected overview of water-glycol formulation chemistry, some of the fluid formulation issues that have been encountered and the evolutionary improvement of hydraulic pump wear performance.

The importance of minimizing air entrainment and enhancing air release in hydraulic fluids has been recognized for over 40 years. These properties are dependent on the composition of hydraulic fluids, especially on the presence of contaminants which inhibit air release and additives which promote it. One objective of this paper is to present an overview of this critically important technology as it has unfolded over the last 40 years. The second objective of this paper is to integrate into this summary recent research results on the impact of additives on air release properties.

The ASTM test method D-2882 (Standard Test Method for Indicating the Wear Characteristics of Petroleum and Non-Petroleum Hydraulic Fluids in a Constant Volume Vane Pump) is widely used to evaluate hydraulic fluids. Performing this method can be difficult due to problems with the pump hardware and the written procedure. This paper discusses the problems and suggests possible remedies.

Hydraulic fluid performance, including water-glycols (W/G), is dependent on the chemical composition of the fluid and cleanliness. An overview of W/G fluid chemistry on pump wear is provided here. Also provided, is a brief overview of the impact of fluid cleanliness on the potential wear properties of various components. Finally, an overview of recommended analytical procedures to assure adequate long-term fluid hydraulic and lubrication performance is provided. If these procedures are followed, substantial improvements in hydraulic pump longevity and performance will be realized.