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Damaged fittings.
Maximum Distance Between Supports for Aluminum Tubing

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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INSTALLATION Leakage of a flared tube assembly is usually caused by the following: Installation of tube assemblies involves a preinstallation check before tube assemblies can be installed. Before you install tube assemblies, check to make sure there are no dents, nicks, and scratches; that the assembly contains the correct nuts and sleeves; that there is a proper fit, where fitting is flared; that a proof pressure test is performed on each assembly; and that the assemblies are clean. To install tube assemblies, hand screw the nuts onto mating connectors. Align the tube assembly in place so that it will not be necessary to pull it into place with the nut. Tubing that runs through cutouts should be installed to avoid scarring when the tubing is worked through a hole. If the tube assembly is long, tape the edge of cutouts before installing the assembly. Torque the nuts. Apply a protective coating to the remaining nonsealed joints after tubing is installed. For disconnected nonsealed joints, apply MIL-S-8802, followed by appropriate paint system, if required. For connected nonsealed joints, apply the first coat of MIL-C-16173, grade 4; 1 hour after applying the first coat, apply the second coat of If an aluminum alloy flared tube assembly leaks MIL-C-16173, grade methods of installing shown in figure 6-21. 4. Correct and incorrect flared tube assemblies are Flare distorted into the nut threads. Sleeve cracked. Flare out of round. Flare cracked or split. Inside of flare rough or scratched. Connector mating surface rough or scratched. Connector threads or nuts are dirty, damaged, or broken. after it has been tightened to the required torque, disassemble it for repair or replacement. If a steel flared tube assembly leaks, it may be tightened one-sixteenth turn beyond the noted torque. If the assembly continues to leak, it should be disassembled for repair or replacement. Do not tighten a nut when there is pressure in the line. Do not overtighten a leaking aluminum alloy assembly. Overtightening may severely damage or cut off tubing flare, or damage sleeve or nut. When you install flareless tube assemblies, proceed as follows:   Make sure no nicks or scratches are evident and the sleeve is preset. Tighten the nut Figure 6-21.—Correct and incorrect methods of installing flared fittings. 6-21







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