ISO/TC 20/SC 10/WG 8 - Hydraulic fluids and fluid contamination control

This document specifies best practice for sampling hydraulic fluid from aircraft hydraulic systems and other hydraulic systems associated with aerospace purposes.

ISO 11218:2017 specifies a cleanliness classification for hydraulic fluids in aeroplanes, helicopters and space vehicles.

ISO 9940:2015 defines technical requirements, qualification and quality control conditions (product qualification, batch control, acceptance) test and measurement methods to be used by manufacturers for qualification of fire-resistant phosphate-ester-base fluids used for hydraulic transmissions in aircrafts.

ISO 14085-4:2015 describes a method for verifying the collapse/burst pressure rating of an aerospace hydraulic fluid power filter element. This represents the capability of a filter element to withstand a designated differential pressure in the normal (intended) direction of flow, created by flowing contaminated fluid through the filter element until either collapse/burst occurs or the maximum expected differential pressure is reached without element failure. The collapse/burst pressure test can be conducted in conjunction with an efficiency test performed according to the procedure defined in the ISO 14085-3 by continuing the contaminant injection until the designated filter element differential pressure is reached. ISO 14085-4:2015 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid or contamination. The tests data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.

ISO 14085-5:2015 specifies a method for determining the resistance of a filter element to flow fatigue caused by varying flow through the filter in various stages of the filter contaminant loading process. The filter is subjected to a uniform varying flow rate for a specified number of cycles, at a number of predetermined differential pressures. Although the number of cycles and differential pressure conditions used in this part of ISO 14085 is meant to simulate possible service conditions, this part of ISO 14085 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid, contamination, and exact cyclic flow conditions. ISO 14085-5:2015 establishes a method for verifying the ability of a filter element to withstand the stress caused by cyclic differential pressures induced by a variable flow rate. The test data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.

ISO 14085-2:2015 specifies - a procedure to thermally condition a hydraulic filter element to presumed aerospace hydraulic system stresses, - a test procedure to complete cold soaks, hot soaks, and temperature variation in a combined manner, and - a test procedure to simulate cold starts. ISO 14085-2:2015 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid or contamination. ISO 14085-2:2015 is intended to provide a test procedure that yields reproducible thermal test conditioning of a hydraulic filter element, for simulation of the thermal stresses typically encountered in an aerospace hydraulic system. The conditioning test procedures defined in this part of ISO 14085 are intended to be used prior to performance tests as specified in other parts of this International Standard. The tests data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.

ISO 14085-3:2015 describes two methods to measure in repeatable conditions the filtration efficiency of filter elements used in aviation and aerospace hydraulic fluid systems. It can be applied when evaluating the overall characteristics of a filter element per ISO 14085‑1, or separately. Since the filtration efficiency of a filter element can change during its service life as it is clogging, this test method specifies its continuous measurement by using on-line particle counters with continuous injection of test contaminant and recirculation of particles not retained by the test filter element until the differential pressure across the element reaches a given final or "terminal" value. ISO 14085-3:2015 allows the efficiency to be measured under both steady or cyclic flow conditions. It also is applied to measure the stabilized contamination levels that are produced by the filter element while testing with cyclic flow. ISO 14085-3:2015 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid or contamination. The tests data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.

ISO 14085-1:2015 specifies a test sequence for evaluation of characteristics of the hydraulic fluid filter elements under standard conditions. ISO 14085-1:2015 is not intended to qualify a filter element under replicate conditions of service; this can only be done by a specific test protocol developed for the purpose, including actual conditions of use, for example the operating fluid or contamination. The tests data resulting from application of this part of ISO 14085 can be used to compare the performance of aerospace hydraulic filter elements.

ISO 14085-6:2015 defines a reference method for determining the level of cleanliness of new filter elements for use in aircraft hydraulic systems, after production prior to shipment, or prior to installation in the circuit. It applies to filter elements used on systems requiring fluid cleanliness conditions defined in the particular specification. The tests data resulting from application of this part of ISO 14085 can be used to compare the cleanliness of aerospace hydraulic filter elements.

ISO 12584:2013 defines the method of reporting and communicating the contamination (or cleanliness) level of components used in aerospace fluid systems. It also presents a coding system which allows cleanliness data to be reported, both in a shortened manner and in a complete manner, when communicating for reporting contamination level measurement results and for specifying cleanliness requirements.

Gives the pressure and characteristics of nitrogen, compressed in oil-lubricated equipment. Is not intended to cover nitrogen für use in oxygen systems. The gaseous nitrogen supply pressure shall ensure charging of aircraft systems up to 343 bar at 20 °C. The minimum purity shall be 98,5 % by volume. It shall contain not more than a total of O,OO5 mg of oil vapour and particulate matter per cubic decimetre of nitrogen at 15 °C and 1 013 mbar.

Specifies the pressure and characteristics of air, compressed in oil-lubricated equipment. Is not intended to cover air for breathing purposes or air for use in oxygen systems. The compressed air supply pressure shall ensure charging of aircraft systems up to 343 bar at 20 °C. The air shall contain not more than a total of O,OO5 mg of oil vapour and particulate matter per cubic decimetre of air at 15 °C and 1 O13 mbar.

Specifies location and criteria for hydraulic system fluid particulate contamination in aeroplanes, helicopters and space vehicles, and provides indirectly related references. Requirements are specified in SAE ARP 4268 which is adopted as a de facto ISO international Standard. For the purposes of international standardization, the outlined modification shall apply to clause 2 of AS4059A.

Requirements are specified in SAE AS4059A which is adopted as a de facto ISO international Standard. For the purposes of international standardization, the outlined modification shall apply to the specific clause of AS4059A.

Specifies procedures for determining the level of contamination. Three procedures are specified herein: microscopic method, automatic particle counting method and gravimetric method. In addition lays down the procedures for cleaning the apparatus and sample bottles, and specifies the solvents to be applied and how these solvents shall be prepared. Requirements as to the selection of the sampling point and to different sampling methods are also specified.