Hydraulic fluids aircraft

Fuel passing through certain hot zones of an aircraft can attain high temperatures moreover it is used to cool lubricants, hydraulic fluids, or air conditioning. It is therefore necessary to control the thermal stability of jet fuels, more particularly during supersonic flight where friction heat increases temperatures in the fuel tanks. 

Hydraulic fluid resistance makes fluorosihcones the preferred military aircraft choice for the manufacture of the flexible bellows (12) between the hydraulic fluid reservoir and the suction pump on Northrop Corp. s T-38 trainers and T-5 fighters. Its use allows for fluid continuity during normal and inverted flight attitudes. 

Resihency provides another opportunity for the mbber functioning as a cushion between stainless steel loop clamps and fuel—hydraulic fluid lines in aircraft. Pratt and Whitney E-lOO military jet engine use (12) provides vibration damping without the clamp abraiding the tube surfaces in normal service as well as at temperatures down to —55°C. 

Resistance to common aircraft fluids such as water, salt water, hydraulic fluid and jet fuel is determined by additional shear testing after exposure to these fluids. Since adhesives are typically only exposed at bond edges, are protected by secondary primers and enamels and are not expected to be exposed to these fluids (save for water) for extended periods, exposure time prior to testing is relatively short. Lastly, the adhesive is tested for propensity to creep rupture under load in standard and aggressive environments. This testing indicates whether the polymer is crosslinked sufficiently to resist long-term creep under low load. 

Another example of the importance of the VI is the need for a high viscosity index hydraulic oil for military aircraft, since hydraulic control systems may be exposed to temperatures ranging from below — 65°F at high altitudes to over 100°F on the ground. For the proper operation of the hydraulic control system, the hydraulic fluid must have a sufficiently high VI to perform its functions at the extremes of the expected temperature range. 

The third class of hydraulic fluids discussed in this profile is the polyalphaolefins. Polyalphaolefins are synthetic hydrocarbons that are made by oligomerizing alphaolefins such as 1-decene (see Chapters 3,4, and 5). Aliphatic hydrocarbons are the principal components of both mineral oils and polyalphaolefins, but the array of hydrocarbons with differing molecular weights is much narrower in polyalphaolefins than in mineral oils. Certain polyalphaolefins maintain good operational characteristics at low temperatures and have been proposed for use in hydraulic systems in U.S. military aircraft (Kinkead et al. 1992b). 

Another group of 14 men was exposed primarily by dermal contact to a triaryl phosphate hydraulic fluid during installation and operation of hydraulic aircraft elevators on a U.S. Navy ship (Baldridge et al. 

Polyalphaolefin Hydraulic Fluids. No human studies for polyalphaolefin hydraulic fluids were located. Polyalphaolefin hydraulic fluids are used in U.S. military aircraft hydraulic systems thus, there is a potential for occupational exposure. Animal studies were insufficient for determining the primary targets of toxicity. Epidemiology studies examining a number of end points would be useful for identifying targets of toxicity. 

Polyalphaolefin Hydraulic Fluids. Polyalphaolefm hydraulic fluids have properties comparable to the most effective components in mineral oil and are used in applications identical to mineral oil hydraulic fluids (Chrisope and Landry 1993 Papay 1993 Shubkin 1993 Wills 1980). Polyalphaolefins are more expensive than mineral oil, and this may limit their use in industry. In addition, polyalphaolefin hydraulic fluids are used in military applications such as aircraft and missile hydraulic systems, tank recoil and hydraulic systems, and aerospace test stands (Shubkin 1993). 

A component of Skydrol 500B and Skydrol LD (tributyl phosphate) was detected in the air at the CP air test facility at Vancouver International Airport at a concentration of 0.04-0.3 mg/m3 (Labour-Canada 1990), indicating that organophosphate ester hydraulic fluids maybe released during aircraft maintenance operations on equipment using organophosphate ester hydraulic fluids. 

Organophosphate Ester Hydraulic Fluids. Organophosphate ester hydraulic fluids are used in applications that require a degree of fire resistance such as in aircraft. EPA (1992b) has noted that aircraft mechanics may have dermal exposures of 1,300-3,900 mg/day and that 2,200 aircraft workers are routinely exposed to tributyl phosphate, while another 43,000 mechanics may be exposed at various times. Estimates of worker exposure in other industries were not found in the available literature. General population and military personnel exposure to organophosphate ester hydraulic fluids is likely to be much lower than exposure to mineral oil hydraulic fluids because these fluids have more specialized uses. 

Organophosphate Ester Hydraulic Fluids. Populations with potentially high exposures to organophosphate ester hydraulic fluids include aircraft mechanics and other mechanics repairing and maintaining hydraulic equipment designed to operate near combustion sources that require fire resistant hydraulic fluids. 

Uses Plasticizer for lacquers, plastics, cellulose esters, and vinyl resins heat-exchange liquid carbonless copy paper systems in aircraft hydraulic fluids solvent extraction of metal ions from solution of reactor products uranium extraction and nuclear fuel reprocessing pigment grinding assistant antifoaming agent solvent for nitrocellulose and cellulose acetate. 

Uses. Antifoaming agent plasticizer for cellulose esters, lacquers, plastic, and vinyl resins component in hydraulic fluids for aircraft control systems... 

Skydrol I Solatia], TM for a series of fire-resistant aircraft hydraulic fluids. 

Phosphate esters have been produced commercially since the 1920s and now have important applications as plasticisers, lubricant additives and synthetic-based fluids for hydraulic and compressor oils. Their first use in lubrication was as anti-wear additives. Later developments in aircraft hydraulic control systems, particularly during the Second World War, introduced phosphate esters as less flammable hydraulic fluids. As esters of orthophosphoric acid they have the general formula OP(OR)3, where R represents an aryl or an alkyl group or, very often, a mixture of alkyl and/or aryl components. The physical and chemical properties of phosphate esters can be varied considerably depending on the choice of substituents [59, 60], selected to give optimum performance for a given application. Phosphate esters are particularly used in applications that benefit from their excellent fire-resistant properties, but compared to other base fluids they are fairly expensive. 

Phosphate esters are also used as hydraulic fluids in civil aircraft where thermal stability is less important than their low-temperature viscosities and cold flow properties. Trialkyl and alkyl-aryl phosphates are used which, when formulated with a VI improver, give fluids with pour points of -55 to -65°C and a VI of 170-300. They are also chosen for other low-temperature applications for conditions such as those found on North Sea, and similar weather condition, oil rigs. 

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