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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/ARP1084AAEROSPACERECOMMENDED PRACTICEARP1084 REV. AIssued 1969-10 Revised 2013-10 Su
5、perseding ARP1084 External Hydraulic Leakage for In-Service Components RATIONALEThis standard has been primarily revised to identify additional components whose external leakage requirements are outside the scope of this document. In addition, there are some additional technical clarifications, the
6、document has been reformatted and some editorial changes have been made. FOREWORDLeakage as hereafter referred to in this document shall mean external leakage. The allowable leakage for hydraulic components has been documented in various military specifications concerning components. The leakage req
7、uirements given in the military specifications are intended in part to control the quality, assembly and proper functioning of the components. However, components that are in service sometimes develop leakage rates in excess of the specified amount. This does not necessarily imply that the component
8、s have degraded to a degree that they no longer provide reliable operation or that they would be detrimental to the system.The intent of this ARP is to establish a level of allowable leakage that will be applicable only to in-service hydraulic components. It is hoped that this will result in minimiz
9、ing what is often the unnecessary removal of hydraulic components from an aircraft. 1. SCOPE The purpose of this SAE Aerospace Recommended Practice (ARP) is to provide guide lines for allowable leakage for in-service aircraft hydraulic components at a nominal 100 F (38 C) temperature and to outline
10、the procedure for measuring such leakage. The limits to be applied to any specific aircraft should be adjusted before inclusion in a maintenance manual.1.1 Application This ARP is applicable to all model aircraft and to all in-service aircraft hydraulic system components. This ARP should not be used
11、 as a basis for acceptance or rejection of components on any bench functional test or systems on new aircraft.This ARP is not applicable to the following: Landing gear oleo struts Liquid springs SAE INTERNATIONAL ARP1084A Page 2 of 4 Self-contained viscous dampers Electrohydrostatic Actuators (EHAs)
12、 Servo actuators incorporating a compensator 2. REFERENCES There are no referenced publications specified herein. 3. LEAKAGE - GENERAL 3.1 Causes of Leakage Leakage of hydraulic components is difficult to describe in a quantitative manner such that it is obvious whether a component is acceptable or
13、unacceptable. Since static or dynamic seals are not functionally perfect, some seepage is normally present. The following are some causes for seepage. a. A film of hydraulic fluid being retained by the finish of metal surfaces, such as piston rods, and being carried past the seal. However, this film
14、 is necessary for the lubrication of the seal. b. Pressure and temperature variations affecting seals. c. Seals tending to take a permanent set after a period of time. d. Detail parts such as cavities retaining fluid. 3.2 Classification of Leakages Leakages can be broadly classified as allowable or
15、excessive, as follows: a. The leakage is termed “allowable” when the fluid escaping is of an insignificant quantity and will have no detrimental effect on aircraft operation, and when correction of this slight leakage does not warrant the maintenance time involved.b. The leakage is termed “excessive
16、” if the fluid leakage is such that the hydraulic reservoir level may be depleted or dangerously lowered during normal operation, or a fire hazard is created, or the air worthiness of the aircraft is otherwise compromised. Allowable leakage, which can exist on even new or overhauled units, will usua
17、lly show as a seepage, stain or wet area. However, it is possible for seepage or an allowable leakage to collect in a cavity of a unit or depression in an adjacent structure over a period of time and falsely indicate excessive leakage. This same leakage when allowed to accumulate on a flat area or a
18、 white painted surface often has the appearance of being excessive. Although the intent of this ARP is to liberalize the allowable leakage for in-service components, some judgment will have to be exercised when this criteria is applied to individual aircraft. It should be apparent that under certain
19、 circumstances itmay be possible to have enough components with allowable leakages such that their combined leakage will come under the classification of “excessive.“ SAE INTERNATIONAL ARP1084A Page 3 of 4 3.3 Measurement of Leakage a. Leakage checks should not be immediately performed on aircraft h
20、ydraulic systems and components that have remained in a static unpressurized condition for an appreciable period of time. The systems should be activated first and the components operated a number of times after which any hydraulic fluid should be wiped off before making leakage checks. b. In some c
21、ases, leakage measurement becomes a problem because the location of the component in the aircraft does not permit direct observation. If there is a flat surface below the component then leakage may be measured by the following method. First wipe the surface clean and place a drop of hydraulic fluid
22、on the area. When this drop stabilizes, note size of area by outlining with a soft lead pencil and wipe clean of hydraulic fluid. Pressurize and cycle the suspected component, correlating the area of the wetted surface with the area previously occupied by one drop. In the event that there is no flat
23、 surface below the component, then a pre-marked panel may be temporarily positioned underneath the component for leakage measurement. c. Where fluid dropping from a component may be directly observed, do not wipe surfaces but pressurize and cycle the component until a drop falls free. Continue opera
24、ting the component until another drop falls and compare results with leakage criteria shown in Table 1. d. For tests requiring long period of time, and where fluid can drop, wipe the surface clean and dry but do not use a solvent. Secure or place a clean blotter or white cloth immediately below the
25、suspected leak. Examine the blotter or cloth after the system has operated or has been idle the required period of time. 3.4 Leakage Rates The allowable leakages for static and dynamic seals for various hydraulic components are listed in Table 1. 4. NOTES 4.1 A change bar (l) located in the left mar
26、gin is for the convenience of the user in locating areas where technical revisions, not editorial changes, have been made to the previous issue of this document. An (R) symbol to the left of the document title indicates a complete revision of the document, including technical revisions. Change bars
27、and (R) are not used in original publications, nor in documents that contain editorial changes only. SAE INTERNATIONAL ARP1084A Page 4 of 4 TABLE 1 - ALLOWABLE LEAKAGES FOR STATIC AND DYNAMIC SEALS FOR VARIOUS HYDRAULIC COMPONENTSCOMPONENTSEALLEAKAGE RATE FUNCTION TYPE Actuating Cylinder Rod Seal Ro
28、d Seal Piston (Vented) End Cap DS-DDS1 drop/5 cycles 1 drop/15 minutes 1 drop/5 cycles 1 drop/5 cycles or 2 drops/day Servo Actuators (Flight Controls) Tandem Piston (Intersystem Vent)Rod Seal Rod Seal End Cap Valve Input Valve Input Servo Ram (Transducer) Pressure Switch Valve Body (Weep Holes) Ele
29、ctro-Hydraulic Servo Valves DS-DDS-DSDS-DDS-DS-DMating Faces 2 drops/5 cycles 4 drops/15 minutes 1 drop/flight hour or 1 drop/20 fullstroke cycles 1 drop/15 minutes 1 drop/5 cycles or 2 drops/day 1 drop/5 cycles 1 drop/5 minutes 1 drop/5 cycles 1 drop/5 minutes 1 drop/5 minutes 2 drops/day Pumps and
30、 Motors Shaft Seal Shaft Seal Housing (Mating Surfaces) DS-DS8 drops/minute 1 drop/minute 2 drops/day Swivels (Coupling, joints, valves, etc.) Low Pressure High Pressure High Pressure SSD1 drop/15 minutes 1 drop/15 minutes 1 drop/5 cycles Valves Body (Weep Hole) Manual Stem Manual Stem Dump Valve SD
31、S-DS1 drop/5 cycles or 2 drops/day 1 drop/5 cycles 1 drop/15 minutes 1 drop/5 cycles or 2 drops/day Reservoirs incorporating a separatorAir/Oil Separated D S-DS2 drops/5 cycles 10 drops/hour 4 drops/day Fittings Flared or Flareless Boss Seals SSNone1 drop/30 minute - a lower rate should be used if t
32、he fitting is readily accessible KEY:D = Dynamic leakage S = Static leakage S - D = Static leakage through dynamic seal NOTES:1. 1.0 cm3is defined as 20 drops. 2. Components in a static condition, as in a parked aircraft, are allowed a maximum leakage of two drops per seal or packing per day. PREPARED BY SAE SUBCOMMITTEE A-6A1, COMMERCIAL AIRCRAFT OFCOMMITTEE A-6, AEROSPACE ACTUATION, CONTROL AND FLUID POWER SYSTEMS
