MIL-DTL-22706G
4.4.5 Bend radius and length. At a stabilized -65°F temperature, the unpressurized duct
assembly shall be subjected to bending until it will not bend further without damage. The
minimum bend radius shall not exceed eight inches as measured to the center line of the duct.
Subsequently, the duct assembly shall be pressurized with air to 30 psia, and the bend radius re-
determined. The bend radius shall not exceed thirty inches without crimping as measured to the
center of the duct. The temperature shall than be stabilized at 130oF and repeated the test
pressurized and unpressurized. After the pressurized bend radius has been determined, the
pressure shall be decreased to 15 psia with a decrement of 5 psia and the change in length shall
be not greater than the value specified in 3.3.1.1.1 The duct assembly shall then be subjected to
the static proof pressure test and leakage test as specified in 4.4.2 and 4.4.3, respectively.
4.4.6 High temperature soak. The duct shall be placed in a chamber and heated to and
maintained at a temperature of 500° +10°F for a period of 30 minutes. At the end of this time,
while in the chamber at 500° +10°F, the duct shall be subjected to a static proof pressure of
150 +2 psia for 5 minutes. Ballooning, bursting, or otherwise failure of the duct to withstand the
above pressure shall be cause for rejection of the duct assembly.
4.4.7 Pressure drop. The pressure drop through a 30-foot section of duct assembly shall
not exceed 6 psi when installed as shown on figure 4 under the flow conditions of 4.4.9.
4.4.8 Adhesion. The outer wall of sample I duct shall have a reinforcement to rubber
adhesion of 15 pounds per linear inch (PLI) minimum when tested in accordance with
ASTM-D413, strip specimen, type A, 180 degree peel machine method. The sample II duct,
upon completion of the 1,000 cycle endurance test, shall be tested at both folded locations (see
figure 4) in accordance with the above procedure, except the ply adhesion shall be 9 pounds PLI
minimum.
4.4.9 Endurance. While installed as shown on figure 4, the duct shall be subjected to a
1,000 cycle test. Each cycle shall consist of air flowing through the duct at the rate of 200 +5
pounds per minute at 100 + 2 psia total pressure with an inlet temperature of 600 +0 oF, -10oF
for one minute followed by one minute of no air flow. The duct shall be flexed 18 inches from
the inlet end as described in 4.4.4 during the no flow portion of the cycle. This total elapsed time
of 2 minutes shall constitute one cycle. The duct shall be in an environment with an ambient
temperature of 130 +5°F, -10°F. A warm-up period of 10 cycles is permissible to establish the
130°F ambient temperature within the tolerances specified. The 1,000 cycle test may be
conducted continuously for a minimum of eight hours.
4.4.10 Fluid resistance. Six exterior adjacent one-foot sections approximately at the
center of a 30-foot duct assembly shall be saturated with each of the following fluids for five
minutes:
a. Test fluid conforming to TT-S-735, Type III.
b. Test fluid conforming to TT-S-735, Type VI.
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