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Commercial Developments
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Most hydraulic fluids are either mineral oils, or one of the four types of fire-resistant fluids, which are oil-in-water emulsions, water-in-oil (invert) emulsions, water-glycol solutions, or phosphate esters. During the 1980s, PAOs and polyol esters were promoted as “fire-resistant” fluids, but it has now been demonstrated clearly that the fire-retardancy properties of these synthetics are very limited.
Hydraulic Fluids and Fluid-Handling Components
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Hydraulic fluids function in a hydraulic system just like blood functions in a human body; it can have a critical impact on performance, reliability, and even a hydraulic system's service life. The importance of selecting the right type of fluid for a hydraulic system can never be overestimated. Making a proper selection requires not only having a basic understanding of the basic fluid characteristics, but also knowing the tasks and working environment of the hydraulic system. Ideally, hydraulic fluids should be inexpensive, noncorrosive, nontoxic, and noninflammable, have good lubricity, and be stable in properties. The technically critical properties of hydraulic fluids include density, viscosity, and bulk modulus. Although no single fluid carries all these ideal characteristics, it is possible to select one that is best for a particular hydraulic system. The commonly used hydraulic fluids in modern hydraulic systems include petroleum-based, environmentally safe, and fire-resistant fluids.
Long-Term Additive Trends in Aerospace Applications
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Carl E. Snyder, Lois J. Gschwender, Shashi Kant Sharma
Hydraulic fluids are operated in closed systems, although the fluid reservoir may be open to air. Hydraulic fluid additives may include antioxidant, antiwear, rubber swell, VI improver, and minor amounts of metal deactivator and dye. (This is a simpler list than that of engine oil, where thermal-oxidative stability is critical.) The application temperature often dictates the additives used. Hydraulic fluids for military applications are defined by the military specifications including MIL-PRF-5606H [20] (mineral oil based fluid) and MIL-PRF-83282D [21] and MIL-PRF-87257 [22] (both synthetic hydrogenated PAO-based fluids). Hydraulic fluids for commercial aircraft that are phosphate ester based are defined by SAE AS 1241 [23].
Tribological Properties of Different Carboxylates in Water–Glycol Hydraulic Fluid
Published in Tribology Transactions, 2022
W/G hydraulic fluids contain water, glycol, thickener, and an additive package. The additive package typically consists of antiwear additives, corrosion inhibitors, and antifoams (3, 8). However, W/G hydraulic fluids exhibit a poorer antiwear property compared with mineral oil-based fluids, which seriously restricts their applications (9, 10). Generally, evaluations of the antiwear properties include two aspects: One is a simulating test, such as the four ball machine and block-on-ring test; the other is a pump test (11). Among various test methods, the pump test is the closest to actual working conditions but requires more time and money.
Management of waste lubricant oil in Europe: A circular economy approach
Published in Critical Reviews in Environmental Science and Technology, 2021
Carolina T. Pinheiro, Margarida J. Quina, Licínio M. Gando-Ferreira
Laundering and reclaiming are suitable for recovery industrial lubricants. Laundering is a closed-loop treatment especially for hydraulic and cut fluids. The process involves the removal of solids by filtration, de-watering by vacuum distillation and the addition of fresh additives. The treated oil returns to the same company for reuse (Totten & De Negri, 2017). Hydraulic fluids can also be treated by reclaiming, where the lubricant is centrifuged and/or filtered and then reused (Monier & Labouze, 2001).