Figure 4-14. Tube and Fitting Alignment

TM 1-1500-204-23-2 Figure 4-14. Tube and Fitting Alignment Figure 4-15. Tubing Fittings (b) Identification of tubing fittings. AN fit- tings are easily Identified by their distinguishing colors; blue for aluminum alloy and black for steel. Aluminum- bronze fittings are cadmium plated, and are not other- wise colored. Only steel fittings are used with steel tubing 3/8-inch outside diameter and smaller. Intermix- ing of tubing and fittings, other than above is permis- sible. (c) Thread compounds. Thread compounds should not be used on flared tubing fitting threads. Use of thread compounds should be limited to tapered male pipe threads. In rare instances, it is possible to obtain a flared tubing fitting manufactured to maximum tolerance which, when coupled to a tubing nut manufactured to minimum tolerance, will be difficult to tighten. If this occurs, organizational, and direct and general support maintenance activities are authorized to apply tape, MIL-T-27730, to the first three threads toreduce friction. Tape should not be allowed on the fitting cone as this will prevent metal-to-metal contact. NOTE Depot level activities, including commercial contractors, affecting overhaul, repair, or modification of service aircraft are prohibited from using antiseize compounds on flared tubing threads. These activities will replace fittings that are manufactured to maximum or minimum thread tolerances. (d) Replace cracked fitting sleeves. Crack- ed fitting sleeves Installed on fuel, hydraulic, water, and pneumatic tubing subjected to pressures up to and including 3000 psi are not considered unsafe and do not need to be replaced unless a leak occurs. If a leak occurs, they must be replaced. An exception to this is when a line is disconnected for any other reason, all cracked fitting sleeves shall be replaced with service- able fitting sleeves. These Instructions also apply to cracked fitting sleeves on return, vent, and drain lines. The above statements are not to be interpreted to mean that a cracked fitting sleeve or sleeves cannot be replaced at the discretion of responsible quality control personnel. Minor surface corrosion on sleeves and fit- tings, while not desirable, is acceptable. Whether or not corroded sleeves and fittings will be replaced is also at the discretion of responsible quality control personnel. (2) Installation and replacement of tubing as- semblies. Before a tubing assembly is Installed in an aircraft, it shall be carefully inspected. Dents and scratches shall be removed, proper nuts and sleeves installed, and a proper fit obtained where tubing is flared. Tubing assembly shall be clean and free from all foreign matter. Sleeve and nuts shall be screwed to mating fitting by hand and nuts tightened with proper wrench. Tubing shall not be pulled into place with the nut, but shall be properly aligned prior to tightening. If tubing assemble is long; edges of cutout shall be taped before tubing is Installed. The fitting wrench or open end wrench shall be used when tightening. Pliers shall never be used to tighten fittings Adjustable open end wrenches may be used only when proper tools are not available. Overtightening nuts may severely damage or completely cut off tubing flares or may result in damage to sleeve or nut of fitting. If nut and sleeve are removed from a section of tubing, and flares are found to retain less than 50 percent of their original wall thickness, tube shall be replaced. Undertightening nuts may also be serious, as this may allow tubing to blow out or leak at fitting because of insufficient grip on flare by sleeve. Use of torque wrenches will prevent undertightening. A nut shall never be tightened to a torque when pressure is on system, as this will tend to cut flare without adding 4-12