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There is an ongoing interest in identifying new biodegradable hydraulic fluid compositions that may be used as alternatives to mineral oil in many hydraulic applications such as mobile off-highway equipment. To date, many basestocks have been proposed including: vegetable oils, polyol esters, diesters, synthetic hydrocarbons and others. One basestock is gaining interest as alternative, biodegradable, fire-resistant hydraulic fluid; anhydrous poly(alkylene glycol) (PAG) fluids. However, the use of these fluids is not new; they are simply being rediscovered. The objective of this paper is to provide an overview of the discovery and development of anhydrous PAGs as hydraulic fluids. This discussion will include: an overview of PAG chemistry, properties and hydraulic pump performance.

Cavitation erosion is one of the most important causes of loss of hydraulic pump efficiency, wear and even failure. Although cavitation process is often understood, there is typically little understanding of the joint role of the hydraulic fluid, which is a component of the system, and the operation of the hydraulic pump. In this paper, an overview is provided that describes the fluid properties that most impact on cavitation damage, the cavitation process within the pump and components and the use of computer simulation to prove improved designs that minimize hydraulic cavitation when various types of fluids are used.

Cavitation is the dynamic process of gas cavity growth and collapse in a liquid. These cavities are due to the presence of dissolved gases or volatile liquids and they are formed at the point where the pressure is less than the saturation pressure of the gas (gaseous cavitation) or vapor pressure (vaporous cavitation). In this paper, various hydraulic system design factors and fluid properties affecting the cavitation process, and bubble collapse mechanisms will be discussed. In-situ generation of cavitation, examination of the cavitation process in model hydraulic systems, material effects and test methods will be reviewed.

Proper hydraulic pump inlet pressure conditions are critical for proper operation of hydraulic systems. This is especially true when water-containing hydraulic fluids are used as direct replacements for mineral oil or synthetic esters. In this paper, the importance of proper inlet conditions on hydraulic system performance will be reviewed. Also provided are various reservoir design recommendations that should be followed when using water-containing hydraulic fluids such as water-glycol (HFC) hydraulic fluids.

With increasing interest in more biodegradable and fire-resistant hydraulic fluids and with the availability of water-glycol hydraulic fluids suitable for high-pressure hydraulic pump operation, there is increasing interest in the conversion of mineral oil hydraulic systems to these alternative fluids. In this paper, the proper conversion procedures and troubleshooting of some common causes of hydraulic failures for the conversion of mineral oil hydraulic fluids to a water-glycol will be reviewed.