Method A. A vapor degreasing method with stabilized trichloroethylene, Federal Specification
O-T-634, shall be used. Proper cleaning is assured by allowing tubing and fittings to remain in vapor degreaser until
operating temperature is obtained. Tubing is blown clean and dried with a stream of clean, dry, water-pumped air. Every
precaution, including sniffing the tubing, should be taken to determine whether tubing and fittings are clean. Oil-pumped
air should be used as a substitute for water-pumped air, because oil would be deposited in tubing. Oxygen, Federal
Specification BB- 0-925, or clean, dry, water-pumped nitrogen, Federal Specification BB-N-411, may be used in place of
Method B. Tubing shall be flushed with naphtha, Federal Specification TT-N-95. Tubing is then
blown clean and dry of all solvent with water-pumped air. Tubing shall be flushed with anti-icing fluid, Military
Specification TT-1-735, or anhydrous ethyl alcohol,
Figure 4-12. Beading Large Tubing
Federal Specification O-E-760, Class A, and rinsed with fresh water. Tubing is dried with a stream of clean, dry, water-
pumped air or by heating at a temperature of 250 to 300 degrees F (121 to 149 degrees C for a suitable period. After
cleaning, aluminum tubing should be treated with a brush coat of chemical film MIL-C-5541. If light corrosion is found,
apply a coat of enamel over chemical film. In cases of severe corrosion pitting, replace the tubing.
Beaded Tubing Joints. Beaded joints are used on low pressure lines. The most practical and rapid way of
forming beads is by using a tool with a rolling action as shown in figure 4-12. Dimensions for beaded joints are given in
Installation of Flared Tubing. Before installing a tube assembly in an aircraft, inspect the line carefully.
Remove dents and scratches, and be sure all nuts and sleeves are snugly mated and securely fitted by proper flaring.
The tube assembly should be clean and free of all foreign matter.
AN parts in tube assemblies. In the manufacture of tube assemblies, an AN818 nut and an MS20819
sleeve are used with the flared end of the tube for attaching tube assembly to other AN parts in the aircraft system. A
AN817 sleeve nut is available for the same functional purpose, but is not widely used (see figure 4-14). All of these
fittings have straight threads conforming to MIL-S-7742. Government Standard fittings have superseded all other types
of fittings, and should be used in preference to all others.
The Department of Defense is in the process of changing AN designations for Government Standard parts
of MS designations. Any information pertaining to AN parts is equally pertinent for MS parts which
supersede AN parts.
Tubing fittings AN 818 and MS 20819. The AN 818 nut is made of steel or aluminum alloy and
MS 20819 sleeves are made from corrosion-resistant steel. These parts are shown installed in figure 4-15. On these
fittings, size is given as a dash number which equals the tubing outside diameter in sixteenths of an inch.