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This report summarizes data relative to liquid fluids and their properties which are of interest to Aerospace Fluid Power technologists.

This document establishes the requirements for physical and chemical properties and the minimum tests to evaluate suitability of phosphate ester hydraulic fluids for use in aircraft systems where fire resistance is required. Additional tests may be specified by the qualifying agency to demonstrate compliance with their specific requirements. The "qualifying agency" will be defined herein to be the airframe manufacturer submitting certification approval for use of the fluid in a specific model airplane. Fluids meeting the requirements of this specification may be approved by a qualifying agency for use on specific airplane models. Data used to show compliance to this specification can be used by the qualifying agency to show compliance to the applicable regulations for the appropriate certifying authority; e.g., FAA, EASA, etc.

This SAE Aerospace Information Report (AIR) presents data on normally accepted changes in physical properties and contamination levels for MIL-PRF-5606, MIL-PRF-83282, and MIL-PRF-87257 hydraulic fluids used in hydraulic test stands. This information is of importance to all users of hydraulic test stands to assure the performance data obtained on these test stands for specific components will not be adversely affected by excessive changes in fluid properties or contamination levels.

This SAE Aerospace Information Report (AIR) provides technical information to assist the development of specific cleaning methods for those filter elements which are designated as "cleanable" and cannot be cleaned by simple and obvious procedures.

This document discusses the relative merits of the physical and chemical properties of hydraulic fluids in relation to the aerospace hydraulic system design, and the related materials compatibility. The discussion in this report applies both to hydrocarbon and phosphate ester based aircraft hydraulic fluids. In some cases, numerical limits are suggested, but, in general, the significance and effect of a property is noted qualitatively.

This SAE Aerospace Information Report (AIR) presents data on hydraulic fluids which are of interest to detail designers of hydraulic systems and components for aerospace flight vehicles. The data pertains to fluids conforming to the following specifications: MIL-PRF-5606 MIL-H-8446 MIL-PRF-27601 (canceled) MIL-PRF-27601 has been canceled without replacement and the data presented herein is for information purposes only. MIL-PRF-83282 MIL-H-53119 MIL-PRF-87257 AS1241 Type IV, Classes 1 and 2, and Type V

This SAE Aerospace Information Report (AIR) presents data on hydraulic fluids which are of interest to detail designers of hydraulic systems and components for aerospace flight vehicles. The data pertains to fluids conforming to the following specifications: MIL-PRF-5606 MIL-H-8446 MIL-PRF-27601 (canceled) MIL-PRF-27601 has been canceled without replacement and the data presented herein is for information purposes only. MIL-PRF-83282 MIL-H-53119 MIL-PRF-87257 AS1241 Type IV, Classes 1 and 2, and Type V

This document establishes the requirements for physical and chemical properties and the minimum tests to evaluate suitability of phosphate ester hydraulic fluids for use in aircraft systems where fire resistance is required. Additional tests may be specified by the qualifying agency to demonstrate compliance with their specific requirements. The "qualifying agency" will be defined herein to be the airframe manufacturer submitting certification approval for use of the fluid in a specific model airplane. Fluids meeting the requirements of this specification may be approved by a qualifying agency for use on specific airplane models. Data used to show compliance to this specification can be used by the qualifying agency to show compliance to the applicable regulations for the appropriate certifying authority; e.g., FAA, EASA, etc.

This document discusses the relative merits of the physical and chemical properties of hydraulic fluids in relation to the aerospace hydraulic system design, and the related materials compatibility. The discussion in this report applies both to hydrocarbon and phosphate ester based aircraft hydraulic fluids. In some cases, numerical limits are suggested, but, in general, the significance and effect of a property is noted qualitatively.

This document reviews briefly the subject of woven metal screens. Conditions that can promote damaging corrosion in stainless steel filter screens are discussed and recommendations are listed for minimizing corrosion damage. This is a general document only; for specific applications it is suggested that the reader refer to the technical literature, and selected references listed below.

Although there is controversy regarding the chemical form of chlorine and its relation to harmful effects in the hydraulic fluid (i.e., chloride ions versus organic chloro-compounds versus total chlorine in all forms), it is generally agreed that total chlorine content should be measured and controlled. In the near future, the ban on the manufacture of chlorinated solvents, out of concern for depletion of the ozone layer, may in itself diminish or eliminate chlorine contamination related aircraft malfunctions. It is generally accepted that hydraulic fluid contamination should be held to a minimum under all conditions. The benefits of low contamination levels are improved performance, lower maintenance due to lower wear, corrosion and erosion, longer fluid life, longer component life, etc. Contaminants can be classified into two general types: those that are insoluble and those that are soluble in the hydraulic fluid.

This report discusses the characteristics of hydraulic fluids and evaluates their importance, not only from the standpoint of fluid formulation, but also in their effect on aero-space hydraulic system design and the materials used in the components of the system. In some cases numerical parameter limits are suggested, but, in general, the effect of a parameter is the basic consideration. Not only must the characteristics of the fluid be considered in the design of a hydraulic system in which it is to be used, but also the characteristics of the system will affect the extent of the importance of the various characteristics of the fluid. In each individual system, as it employs a fluid, the characteristics of the fluid must be assessed with their immediate import and weighed in considering their effects on the system design requirements based upon the variables of system environment, function and basic design.

This document discusses the relative merits of the physical and chemical properties of hydraulic fluids in relation to the aerospace hydraulic system design, and the related materials compatibility. The discussion in this report applies both to hydrocarbon and phosphate ester based aircraft hydraulic fluids. In some cases, numerical limits are suggested, but, in general, the significance and effect of a property is noted qualitatively.

This SAE Aerospace Information Report (AIR) presents data on hydraulic fluids which are of interest to detail designers of hydraulic systems and components for aerospace flight vehicles. The data pertain to fluids conforming to specifications MIL-H-5606, MIL-H-8446, MIL-PRF-27601, MIL-PRF-83282, MIL-H-53119, MIL-PRF-87257, Aerospace Standard 1241 Type IV, Classes 1 and 2, and Type V. The relative merits of hydraulic fluid properties in relation to the fluid formulation, aerospace hydraulic system design and the related materials compatibility are discussed in AIR81, Hydraulic Fluid Properties. This document is essentially a metric document with English units available in the data charts for convenience. There is a treatment of conversions between ISO and English units in AIR1657.

This document reviews briefly the subject of woven metal screens. Conditions that can promote damaging corrosion in stainless steel filter screens are discussed and recommendations are listed for minimizing corrosion damage. This is a general document only; for specific applications it is suggested that the reader refer to the technical literature, and selected references listed below.

This SAE Aerospace Recommended Practice (ARP) establishes a method for evaluating the particulate matter extracted from the working fluid of a hydraulic system or component using a membrane. The amount of particulate matter deposited on the membrane due to filtering a given quantity of fluid is visually compared against a standard membrane in order to provide an indication of the cleanliness level of the fluid. A particular feature of this method is the membrane preparation to achieve an even particulate distribution on the membrane suitable for other applications. Membrane evaluation using standard membranes, described in this document, is an alternative technique to counting with either an optical microscope (ARP598) or an automatic particle counter (ISO 11500). The latter particle counting procedures are considered more precise.

Although there is controversy regarding the chemical form of chlorine and its relation to harmful effects in the hydraulic fluid (i.e., chloride ions versus organic chloro-compounds versus total chlorine in all forms), it is generally agreed that total chlorine content should be measured and controlled. In the near future, the ban on the manufacture of chlorinated solvents, out of concern for depletion of the ozone layer, may in itself diminish or eliminate chlorine contamination related aircraft malfunctions. It is generally accepted that hydraulic fluid contamination should be held to a minimum under all conditions. The benefits of low contamination levels are improved performance, lower maintenance due to lower wear, corrosion and erosion, longer fluid life, longer component life, etc. Contaminants can be classified into two general types: those that are insoluble and those that are soluble in the hydraulic fluid.

This SAE Aerospace Recommended Practice (ARP) describes two procedures for sampling particles in dust controlled spaces. One procedure covers airborne dust above 5 μm. The other (and newly added procedure) covers particles of 25 μm and larger that “fall out” of the environment onto surfaces. In each case the particles are sized in the longest dimension and counted. Airborne particles are reported as particles per cubic meter (cubic foot) whereas particles collected in fall out samples are reported as particles per 0.1 square meter (square foot). This document includes English units in parentheses as referenced information to the SI units where meaningful. These procedures may also be used for environmental analysis where the quality of the particles by visual or chemical analysis is intended.

This document discusses the relative merits of the properties of hydrocarbon-based hydraulic fluid in relation to the fluid formulation, aerospace hydraulic system design and the related materials compatibility. In some cases, numerical limits are suggested, but, in general, the effect of a property is noted qualitatively. The properties of the fluid must be considered in the design of a hydraulic system, but it is possible to design a system to be less sensitive, or more robust, to a particular fluid property. For this reason, the property of the hydraulic fluid must be weighed for each individual hydraulic system, taking into account the system's basic design, function and environment, as well as the fluid toxicity and disposal issues. Besides the hydraulic system itself, ground handling and servicing needs of the system must also be considered. The only absolute characteristic of a hydraulic fluid is that it be a liquid throughout the range of use.