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
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