MIL-DTL-25531F
coupling being rotated 72 degrees after every 25 drops and reheated to an internal surface
temperature of 600°F after every 25 consecutive drops. This procedure shall be repeated for 125
disconnects when the coupling and nipple are mounted in the vertical position with the flange
and nipple 6 feet above the surface. Upon completion of this test, the coupling shall be subjected
to the test specified in 4.6.3.
4.6.7 Safety device.
4.6.7.1 Safety valve. The proper and reliable operation of the automatic self-closing valve shall
be demonstrated in accordance with 4.5.2. The coupling attached to one end of a 10 to 30 foot
length of ducting shall be placed on level concrete with the duct making a large radius angle of
90 degrees and the coupling end free to move. Air at 112 psia shall be applied to the duct. After
initial straightening of the duct, there shall be no perceptible movement of the coupling end of
the duct. The proper operation of the safety valve shall be demonstrated by the following
procedure. With the pressure lock deactivated, the coupling attached to the nipple, and with air
flowing under a pressure of 80 psia and stabilized at 600°F, handling ring actuation of the
coupling shall cause the coupling to disconnect and instantaneously close the safety valve. As a
safety precaution, the coupling end of the house shall be suitably restrained.
4.6.7.2 Pressure lock. The coupling, engaged with a nipple, shall be subjected to 112 psia. A
coupling release shall be attempted at this pressure. The pressure shall then be reduced in
increments of 10 psi and at each increment the handling ring shall be pulled three times with
sufficient force to provide a component parallel to the coupling axis of 25 to 35 pounds.
Disconnection of the coupling when a pressure above 10 psi is applied or failure of the pressure
lock to operate satisfactorily as a result of this test shall be cause for rejection.
4.6.8 Endurance. The coupling shall satisfactorily complete the following endurance test, after
which it shall be subjected to the test specified in 4.6.3. Only one nipple shall be used throughout
this test. Any galling or distortion of the nipple that would be detrimental to proper engagement
or release of the coupling shall be cause for rejection.
a. Cyclical: The coupling shall be engaged and disengaged to the nipple a total of 1,000
times. The engagement and disengagement shall be accomplished after the coupling has been
subjected for 1 minute to an air flow of 100 to 188 pm at a total air pressure and temperature of
80 psia and 500°F, respectively. The cycle shall be conducted at intervals of approximately 4
minutes.
b. Continuous: The coupling shall be subjected to 50 cycles, each cycle being 2 hours
duration. During 1 hour of the cycle, air shall be flowed through the coupling at the rate of 100 to
188 pm at a total air pressure and temperature of 80 psia and 600°F, respectively. During the
second hour there shall be no air flow. The coupling shall be released from the nipple following
the 1-hour flow period and shall be reengaged following the 1-hour no-flow period.
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