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Installation of Teflon backup rings (internal)
Protective Closures

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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Backup rings may be installed singly, if pressure acts only upon one side of the seal. In this case, the backup ring is installed next to the O-ring, opposite the pressure force. See view A of figure 2-51. When dual backup rings are installed, the split scarfed ends must be staggered, as shown in view B of figure 2-51. View C of figure 2-51 shows an improper dual ring installation. Wipers Wipers (scrapers) are used to clean and lubricate the exposed portion of piston shafts. This prevents foreign matter from entering the system and scoring internal surfaces. Wipers may be of the metallic (usually copper base alloys) or felt types. They are used in practically all landing gear shock struts and most actuating cylinders. At times, they are used together, the felt wiper being installed behind the metallic wiper. Normally, the felt wiper is lubricated with system hydraulic fluid from a drilled bleed passage or from an external fitting. Wipers are manufactured for a specific hydraulic component and must be ordered for that application. Wipers are normally inspected and changed, if Figure 2-51.—Teflon® backup ring installation (external). 2-40







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