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 2013 SAE International All rights reserved. No part of this p
3、ublication 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: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR825/5A AEROSPACE INFORMATION REPORT AIR825/5 REV. A Issued 2002-03 Revised 200
5、3-03 Reaffirmed 2013-12 Superseding AIR825/5 Liquid Oxygen Systems RATIONALE AIR825/5A has been reaffirmed to comply with the SAE five-year review policy. FOREWORDThis document is one of a set of related documents. These documents comprehensively address the “Introduction to Oxygen Equipment for Air
6、craft“, and are referred to as slash (/) documents, rather than chapters. The documents may be obtained as a set or individually. As the field of oxygen systems for aircraft has evolved, it became cumbersome for one document to cover the full range of subject matter. The reader who is seeking overal
7、l familiarity with oxygen systems for aircraft should read all of these documents that combine to form a general reference to oxygen systems. The reader who is familiar with oxygen systems for aircraft may want to obtain only the slash documents that pertain to topics that are of specific interest.T
8、he document set is written as an introductory level, suitable for anyone who would like to understand the basics of oxygen systems in aircraft, and specifically for the engineer who has just recently been assigned to aircraft oxygen systems. Many of these documents point the reader toward more detai
9、led treatments located in other SAE documents.TABLE OF CONTENTS1. SCOPE .32. REFERENCES .32.1 Applicable Documents .32.1.1 SAE Publications .32.1.2 U.S. Government Publications.32.1.3 NFPA Publications .32.2 Related Publications 42.3 Definitions 43. LIQUID OXYGEN (LOX).43.1 LOX Properties 5TABLE OF
10、CONTENTS (Continued)3.2 LOX Converters and Ground Servicing Equipment .53.2.1 LOX Converter Assembly.83.2.2 LOX Ground Servicing Equipment .123.3 Precautionary Measures 163.3.1 Possible Injury from Cold .163.3.2 Clothing and Protective Equipment163.3.3 Clothing Safety Measures 163.3.4 Treatment for
11、LOX Contact 163.3.5 Precautions on Transferring LOX.163.3.6 Material in Contact with LOX163.3.7 Ground Surfaces in Transferring LOX173.3.8 Electrical Grounding Requirements173.3.9 Lubricants in LOX.173.3.10 Storage Requirements of LOX .173.3.11 Location of Storage Containers173.3.12 Vacuum Failure 1
12、73.4 Comparison of Liquid Versus Gaseous Oxygen 183.4.1 Advantages of LOX 183.4.2 Disadvantages of LOX .193.5 Design Issues for Aircraft Installation.203.5.1 Oxygen System Sizing .203.5.2 Heat Exchanger Requirements 203.5.3 Tubing Requirements .213.5.4 Pressure Relief Concerns 213.5.5 Recharger Outl
13、ets 213.5.6 Purging and Cleaning LOX Converters and Supply Equipment.223.5.7 Other LOX System Features Necessary for Maintenance and Safety.224. NOTES224.1 Keywords .22SAE INTERNATIONAL AIR825/5A Page 2 of 22_1. SCOPE:This Aerospace Information Report provides general information to aircraft designe
14、rs and engineers, regarding LOX, its properties, its storage and its conversion to gas. Much useful information is included herein for aircraft designers regarding important design considerations for a safe and effective installation to an aircraft. The associated ground support equipment needed to
15、support operations of LOX equipped aircraft is also discussed. It is important to realize that LOX equipped aircraft cannot be supported unless this support infrastructure is also available. A significant part of this document will address the specific advantages, disadvantages and precautions relat
16、ing to LOX systems. These are important issues that must be considered in deciding which oxygen system to install to the aircraft. Also, many commercial and military aircraft use aeromedical LOX equipment that is mostly portable equipment. Aeromedical LOX equipment is not addressed herein as it is b
17、eyond the scope of this document.2. REFERENCES:2.1 Applicable Documents:The 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
18、 purchase order. In the event of conflict between the text of this document 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.2.1.1 SAE Publications: Ava
19、ilable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.AS8010 Aviators Breathing Oxygen Purity Standard2.1.2 U.S. Government Publications: Available from DODSSP, Subscription Services Desk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 19111-5094.MIL-PRF-27210 Oxygen, Aviators Breath
20、ing, Liquid and Gas2.1.3 NFPA Publications: Available from National Fire Protection Association, 11 Tracy Drive, Avon, MA 02322.NFPA Standard No. 401 BSAE INTERNATIONAL AIR825/5A Page 3 of 22_2.2 Related Publications:The following publications are provided for information purposes only and are not a
21、 required part of this SAE Aerospace Technical Report.MIL-D-19326 Design and Installation of Liquid Oxygen Systems in Aircraft,General Specification forTR-56-260 Air Force Handbook of LOX Systems, Volumes I that is, the filler valve assembly and the build-up and vent valve assembly. In portable conv
22、erter designs, these assemblies may be part of the converter assembly. Most designs that are available now combine the functions of the two assemblies into one unit.3.2.1.6 Converter Vacuum: The principle part of the converter is a vacuum insulated container. It consists of an inner and an outer she
23、ll with an evacuated air space between the two walls. Connections for filling and removing the LOX, and for venting the gaseous oxygen are provided between the two concentric containers. Heat transfer from outside the converter to the inner shell can be reduced by the following design features:a. Ev
24、acuated space between the shells.b. Most aircraft containers within the converter have a molecular “getter“ in the near vacuum evacuated space to provide adsorption of air molecules at cryogenic temperatures. This improves the insulation for the required efficiency to be practical for use with small
25、er containers on aircraft. Most ground support and transfer storage containers use insulating powder between the walls for additional insulation. Both types of storage containers use silvered and/or highly polished surface treatment of the walls forming the evacuated space.c. Use of low thermally co
26、nductive materials in the assembly and a minimum number of support and/or assembly points between the two shells.SAE INTERNATIONAL AIR825/5A Page 10 of 22_3.2.1.7 Pressure Relief: Despite the low heat transfer through the walls and assembly points of the converter assembly, there will always be some
27、 heat transfer and some evaporation of LOX. Pressure relief valves must be provided to allow the escape of gas and to prevent dangerously excessive pressure build-up when the oxygen in the oxygen converter is not being expended to the supply line. For reasons of safety to prevent a LOX converter exp
28、losion, two pressure relief devices are usually included. The customary design practice on smaller LOX converters is that one is LOX converter mounted and the secondary pressure relief is aircraft mounted. On larger LOX converters, both pressure relief valves are on the LOX converter. One pressure r
29、elief valve called secondary relief is set at a slightly higher pressure setting than the primary relief valve. This enables the system to vent a greater amount of oxygen gas if needed to prevent over pressurization of the LOX converter while at the same time minimizing LOX overboard venting for the
30、 much longer time periods when slow oxygen gas venting is needed.3.2.1.8 Purge Valve: On larger containers it may be necessary to purge the container for maintenance. It would be impractical to let the liquid oxygen evaporate by the normal means of loss of supply through the pressure relief from the
31、 gradual warming of the LOX supply. This would take many days. Therefore a purge valve is fitted to the lower part of the container to evacuate the remaining liquid before maintenance3.2.1.9 Oxygen Losses: In present day equipment, losses of LOX from a converter assembly range from 5 to 20% in 24 h
32、depending on size and insulation efficiency of the container. Smaller LOX converters have a greater loss than larger converters as they have less volume of LOX per surface area of the container. Five (5) liter LOX converters lose up to 20% and 75-L LOX converters lose up to 5% in 24 h with existing
33、LOX converters. There will be a maximum 15% filling loss on servicing the LOX converter depending on the skill of the person doing the servicing operation and the method and time period of stabilization of the LOX converter. The evaporation losses given above are percentages of LOX container size ir
34、respective of the loss encountered during LOX servicing and stabilization.3.2.1.10 Converter Types: Most existing airborne converters designs that are smaller deliver gaseous oxygen at a pressure of 0.48 MPa (70 psig). These converters hold about 5, 8, 10, or 12 L of LOX. The 8-L converters have the
35、 same outline dimensions as the 5-L converters. The 12-L converters have the same outline dimensions as the 10-L converters. A number of larger converters that hold 25 or 75 L of LOX have been produced that deliver 2.07 MPa (300 psig) gas for use on aircraft with more persons. The higher operating p
36、ressure is needed to support many oxygen outlets normally provided on transport aircraft. The higher-pressure assemblies are also installed on transport aircraft to permit the crew to refill their portable oxygen bottles directly from the aircrafts oxygen system. Proper function of all downstream va
37、lves and regulators is provided with the 300 psig, as pressure losses in large systems are unavoidable. The higher-pressure airborne converter assemblies have also been studied for use in the commercial jet transport aircraft. Long supply tubing runs are required with associated line pressure drop.
38、Also, high flow rates are required during emergency use of this system. A pressure of 300 psig is essential to allow higher delivery flow rates.SAE INTERNATIONAL AIR825/5A Page 11 of 22_3.2.1.11 Servicing Converters: Converter assemblies may be filled at the aircraft or removed and filled at a remot
39、e location depending on converter design. Removable converters are designed with a wedge plate mounting that enables rapid removal and replacement. Removable converters are mainly used on smaller military aircraft and can be filled with LOX at the aircraft or at the flight line location. The almost
40、universally accepted practice now is to remove the converters the night before and fill them all at once. This is done at the flight line where they are stabilized for several hours. They are reinstalled before the next aircraft flight. This keeps all servicing LOX risks and hazards minimized. Fixed
41、 installation converters must be filled at the aircraft where the fill build-up and vent valves are mounted to the aircraft exterior versus on the converter for removable converters. Hazards are minimized through training and procedures.3.2.1.12 Converter Displays: Liquid quantity indicating equipme
42、nt used with converters is available in three types using different design features: Capacitance gauging, electro-mechanical transducer indication, and differential pressure type. Many modern LOX converters use capacitance gauging with a probe mounted vertically in the LOX within the converter. The
43、height or level of the LOX sets the value of the capacitance enabling an electronic signal to be transmitted to the cockpit gauge or display. Differential pressure gauging was used in the past and is still used. It measures the difference of pressure between the top and bottom on the LOX container t
44、hat is a function of the liquid volume. Pressure gauging is often used on the gas side of the aircraft LOX system.3.2.2 LOX Ground Servicing Equipment: Special storage tank and transfer cart assemblies provide ground-servicing equipment for aircraft LOX systems. LOX can be stored indefinitely at sea
45、 level as long as it is kept at a temperature below its boiling point. Maintaining a temperature below -182.8 C (-297 F) by mechanical refrigeration is expensive and impractical. Therefore, LOX is usually stored and handled in vacuum-insulated containers. The pressure buildup within a LOX storage co
46、ntainer is obtained by vaporization of the LOX. Control valves can regulate this. This energy can be used to provide the optimum pressure 0.21 to 0.27 MPa (30 to 40 psig) for transfer of LOX from the ground equipment to an aircraft converter installation or to another storage tank. For larger conver
47、ters it may be necessary to service with a higher pressure. When servicing to a container of lower pressure and higher temperature through the plumbing, the phenomena of “flashover“ is observed where the LOX is bubbling and boiling and is greatly agitated. Safe existing practices are to install a ve
48、nt tool or cap on the container after servicing to keep pressures nearly atmospheric until stabilization occurs to preclude freeze up of the converter valves. To provide destratification the converter must be then stabilized at the converter head pressure usually 5 to 12 h after servicing. The vent tool or cap can then be removed and allow stable pressure
