1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions.Copyright 2014 SAE International All rights reserved. No part of this pu
3、blication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970
4、 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP5891AEROSPACERECOMMENDED PRACTICEARP5891Issued 2008-01 Reaffirmed 2014-05 Achiev
5、ing Cleanliness Standards for Aircraft Hydraulic Systems During Manufacture RATIONALEARP5891 has been reaffirmed to comply with the SAE five-year review policy. TABLE OF CONTENTS 1. SCOPE 2 2. APPLICABLE DOCUMENTS 2 2.1 SAE Publications. 2 2.2 U.S. Government Publications 2 3. GENERAL . 3 3.1 Outlin
6、e of Build Process 3 3.1.1 Tube Fabrication . 3 3.1.2 Tube Assembly . 3 3.1.3 Tube Installation 3 3.1.4 Installation Leak Check and Pressure Test 4 3.2 System Cleanup 4 3.2.1 Tube Flushing . 4 3.2.2 Factors Which Effect Flushing 5 3.2.3 Recommended Flow Rates. 6 3.3 Recommended Planning. 7 3.3.1 Flu
7、shing Kit Definition and Procurement 7 3.3.2 Establishing a Written Plan . 7 3.4 System Fill. 9 3.5 System Functional Checkout 9 APPENDIX A 17 FIGURE 1 EXAMPLE FLUSHING CIRCUIT 10 FIGURE 2A RECOMMENDED FLUSHING FLOW RATES FOR AS1241 TYPE IV CLASS 2 FLUID 11 FIGURE 2B RECOMMENDED FLUSHING FLOW RATES
8、FOR AS1241 TYPE IV CLASS 2 FLUID (ISO UNITS). 12 FIGURE 3A RECOMMENDED FLUSHING FLOW RATES FOR MIL-PRF-83282 FLUID 13 FIGURE 3B RECOMMENDED FLUSHING FLOW RATES FOR MIL-PRF-83282 FLUID (ISO UNITS). 14 FIGURE 4A RECOMMENDED FLUSHING FLOW RATES FOR MIL-PRF-87257 FLUID 15 FIGURE 4B RECOMMENDED FLUSHING
9、FLOW RATES FOR MIL-PRF-87257 FLUID (ISO UNITS). 16 1. SCOPE This SAE Aerospace Recommended Practice (ARP) establishes the processes to achieve and maintain the required cleanliness levels in flight vehicle hydraulic systems during fabrication, assembly and pre-flight functional tests. This recommend
10、ed practice covers exclusion and removal primarily of solid contaminants that occur or are created during these successive steps. The flushing procedure for installed tubing is detailed. This ARP does not address contamination levels of hydraulic fluids as purchased, operation and maintenance of gro
11、und carts, details of component cleanliness or of contamination measurement. This ARP applies to military aircraft and helicopters designed to AS5440, commercial aircraft hydraulic systems designed to ARP4752 and commercial helicopter hydraulic systems designed to ARP4925. 2. APPLICABLE DOCUMENTS Th
12、e following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this documen
13、t and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-
14、0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. ARP994 Recommended Practice for the Design of Tubing Installations for Aerospace Fluid Power Systems AS1241 Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft AIR1362 Aerospace Hydraulic Fluids Physi
15、cal Properties AS4059 Aerospace Fluid Power - Cleanliness Classification for Hydraulic Fluids ARP4752 Aerospace - Design and Installation of Commercial Transport Aircraft Hydraulic Systems ARP4925 Aerospace - Design and Installation of Commercial Transport Helicopter Hydraulic Systems ARP5376 Method
16、s, Locations and Criteria for System Sampling and Measuring the Solid Particle Contamination of Hydraulic Fluids AS5440 Hydraulic Systems, Aircraft, Design and Installation Requirements for 2.2 U.S. Government Publications Available from Document Automation and Production Service (DAPS), Building 4/
17、D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-697-6257, http:/assist.daps.dla.mil/quicksearch/. MIL-PRF-83282 Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Aircraft, Metric, NATO Code Number H-537 MIL-PRF-87257 Hydraulic Fluid, Fire Resistant; Low Temperature, Synthetic
18、 Hydrocarbon Base, Aircraft and Missile, NATO Code Number H-538 MIL-STD-419 Cleaning, Protecting, and Testing Piping, Tubing, and Fittings for Hydraulic Power Transmission Equipment SAE INTERNATIONAL ARP5891 Page 2 of 18_ 3. GENERAL There are many steps in the fabrication and assembly of an aircraft
19、 hydraulic system. Tube extrusion requires lubricants for the dies. Tube bending requires lubricant for the bend mandrels. Cutting processes trim the tube stock to finished length. During many of the steps, solid contamination is created to some extent, affecting the cleanliness of the tubing or com
20、ponents in the system. Some processes produce no contamination; others create metal chips or expose the tube or component to the surrounding environment, which will affect the final cleanliness of the system. This ARP outlines the major steps of the build process and makes recommendations which cont
21、ribute to the achievement of the overall, final cleanliness level required. 3.1 Outline of Build Process The following steps generally describe the fabrication, assembly and functional test stages for the aircraft hydraulic tubing system and prescribe steps for achieving a clean system. 3.1.1 Tube F
22、abrication The stock tubing lengths are formed according to the defined bend data on applicable tube detail or assembly drawing for each tube assembly. Following forming, the tubes should be subjected to a cleaning process which removes solid contaminants and forming lubricants from the interior and
23、 exterior of the tube detail. The cleaning method varies, but usually involves a degreasing operation of the tube followed by a rinse operation to give a clean, non-tacky interior and exterior surface on the tube. Following the degreasing process, the tubes should be capped or bagged to maintain cle
24、anliness for the next operation. MIL-STD-419 has detailed recommendations on cleaning of tubes. 3.1.2 Tube Assembly Following forming, cleaning and degreasing, fittings are attached to those tubes as called up on the tubing assembly drawing. If required, tubes which have one or more permanent fittin
25、gs will be trimmed to a length with allowance for final trim in preparation for final installation. The completed assembly is subjected to proof pressure test and identification and function tapes are applied. There are several points of quality inspection that may be applied during and following th
26、e prescribed steps: 1. The cleanliness of the fluid used for proof pressure testing should be controlled to one or two levels cleaner than the final system in order to help meet final cleanliness requirements. 2. The use of air or water for proof pressure test prevents the tube interior from becomin
27、g tacky and prone to pick up contamination. Either media should be cleaner than the final system as noted above to promote meeting delivered cleanliness level requirement. 3. Tube assemblies should be drained, dried and capped, bagged or plugged upon completion of this operation using fluid compatib
28、le materials for the caps and plugs. 3.1.3 Tube Installation As the airframe subsections progress through their build process, the formed tubing is installed and clamped in accordance with released installation drawings. Usually the system components are in place to the maximum extent possible in or
29、der to use the components to establish the final, installed position of the tubing. During this stage, tubing which requires in-place permanent joints will be trimmed, deburred and joined. This operation can be one source of solid contaminant within the tube assemblies. Contamination generated by th
30、is operation must be removed by flushing as detailed in 3.2 of this specification, prior to operation of components, to avoid lodging contaminant within close tolerance parts in valves, actuators and other components. It will help to reduce contamination generation at the system level if the design
31、of permanent joints between major airframe sections is such that no trimming is necessary. SAE INTERNATIONAL ARP5891 Page 3 of 18_ 3.1.4 Installation Leak Check and Pressure Test Leak testing at this point allows easier access in event of a leaking joint. The assembled tubing, with pressure tight pl
32、ugs at end points, will be subjected to a low-pressure nitrogen leak check. Leaks detected at this point are corrected. Once no leakage is ascertained, the tubing is subjected to the appropriate pressure for the prescribed time. At this point, sections of tubing joined at this stage will receive a p
33、ressure test with the components removed. The tubing in major airframe sections may be pressure tested as an assembly prior to joining with other sections in final assembly. 3.2 System Cleanup 3.2.1 Tube Flushing 3.2.1.1 Need for Flushing Flushing is used in order to remove the solid contaminants ge
34、nerated during the tube fabrication, installation, and assembly process with a high degree of confidence in the result. Unless verifiable Quality Control standards are used to guarantee that no contamination of a tube assembly has occurred during the previous processes, steps to eliminate any contam
35、inant previously generated are needed. Once all tubing is installed and all tube joints completed, components must be removed and flushing of each tube path should be conducted to reduce any solid contamination to an established standard. NOTE: For aircraft hydraulic systems, the flushing procedures
36、 of this document are more relevant than MIL-STD-419 flushing procedures and should be used in lieu of MIL-STD-419 procedures whenever possible. 3.2.1.2 Flushing Definition Flushing is defined as the sequential application of sufficient flow through each tube circuit to produce turbulent flow in the
37、 circuit. For this document, a conservative Reynolds number value of 4000 is used. 3.2.1.3 Cleanliness Standard A standard of at least one level cleaner than the final delivered cleanliness is recommended. Example: If cleanliness of AS4059 Class 7 is required for delivery, Class 6 should be a goal d
38、uring buildup. Components shall be sufficiently cleaned that a fluid sample taken from a filled component should meet AS4059 Class 5 cleanliness requirements. This tiered approach will simplify clean-up of the system in final stages when assembly of the system is complete. 3.2.1.4 Sampling Problems
39、Interim contamination testing on fluid samples at this stage for completed major sub-sections is conducted to verify cleanliness. The conditions for fluid samples are often not ideal at this stage of build-up. If care is not exercised in the processing of bottled samples the results may be one or po
40、ssibly two classes dirtier than obtained with on-line sampling. Taking of return fluid samples directly into sample bottles may be done, but does not always give a representative sample, as the initial discharge of fluid may contain higher levels of contamination. The practice of establishing a stre
41、am of fluid into a waste container, then switching to a clean sampling bottle without disturbing anything will improve sampling into a clean bottle. The sampling process can be improved by use of a valve designed for sampling assembled to a clean hose that is connected to the return side of the sect
42、ion being flushed. A proper sampling valve installed in the return line from the aircraft system at the ground cart will aid in getting representative samples. Continuous on-line sampling of the return fluid going back to the ground cart is a time saving process, eliminating the time loop required f
43、or taking samples, submission to the lab for analysis and getting a report on results. For additional discussion on sampling refer to ARP5376. SAE INTERNATIONAL ARP5891 Page 4 of 18_ 3.2.1.5 Flushing Tool Kit Flushing of the aircraft hydraulic system should be supported by a defined “tool kit” consi
44、sting of a selection of hose sizes and lengths, and adapter fittings in the various tube sizes to accommodate each installation. The kit should include industrial ball or needle valves, and any special assemblies of hose, tubing, and valve(s) needed to flush dense, low access areas. All fittings, ho
45、se, and valves in the kit should be rated for the highest pressure to be applied while installed. This would usually be proof pressure. The jumper hose, shut-off valves and other tooling used in the flushing process should be drained and capped when not in use to help maintain cleanliness. 3.2.1.6 F
46、lushing Power Source Flushing of tubing is accomplished by using a ground cart or central hydraulic system with a high capacity industrial filter in the return circuit. The ground cart return filter should be rated to at least the level of the finest filter in the aircraft. Fluid used shall be the s
47、ame fluid specification as approved for the aircraft hydraulic system. It is essential that the fluid used for flushing be periodically checked for cleanliness and acceptable values for water content and acidity. The fluid should be maintained at one to two levels cleaner than the requirement for th
48、e aircraft system. Use of a commercial fluid purifier on the hydraulic power source used for flushing will reduce fluid waste and maintain high quality fluid for repeated usage. 3.2.2 Factors Which Effect Flushing 3.2.2.1 Generation of Turbulent Flow For flushing, the ground cart pressure is raised just enough to force fluid through each circuit in the system at a flow rate which guarantees turbulent flow. Conservatively, a Reynolds Number of at least
