MIL-DTL-25427B
temperature of 275 °F ±5 °F for a period of 6 hours. There shall be no measurable leakage from
the connected coupling during the 6 hour period. At the end of this period, the coupling shall be
cooled to 140 °F ±5 °F and at least five cycles of coupling and uncoupling shall be completed.
There shall be no binding during any cycle of disconnection and connection. The temperature of
the uncoupled halves shall be raised to 225 °F ±5 °F and shall be subjected to a leakage at low
pressure test (see 4.8.5.1) and then subjected to a leakage at high pressure test specified in
4.8.5.2.
4.8.8.2 Low temperature. After completion of the high temperature tests (see 4.8.8.1),
the couplings shall be connected to a 30-inch static pressure of hydraulic fluid and subjected to a
temperature of -65°F for a period of 4 hours after stabilization. There shall be no measurable
leakage from the connected coupling during this period. At the end of this period, at least five
cycles of coupling and uncoupling shall be completed. There shall be no binding during any
cycle of disconnection and connection. The uncoupled halves shall be subjected to leakage at
low pressure test (see 4.8.5.1) and then subjected to leakage at high pressure test (see 4.8.5.2).
This requirement shall be satisfactory for the temperature rising to -40°F during this test.
4.8.9 Rapid warm up. The coupled coupling while connected to a 30 inch static head of
hydraulic fluid, shall be allowed to warm up rapidly from -65 °F to +40 °F within a 5 minute
period and shall be coupled and uncoupled at least five times during this period without waiting
for the fluid, coupling, and ambient air temperature to stabilize. The test temperature shall be
measured at coupling outer surface. During the coupling and uncoupling process, the coupling
shall be observed for any malfunction.
4.8.10 Proof pressure. The coupled coupling and the uncoupled halves shall be subjected
to a proof pressure of 150 percent of the rated pressure for a period of one (1) minute at room
temperature. There shall be no leakage greater than to form a drop or any permanent distortion or
other malfunctioning of the coupling. The coupling shall couple and uncouple normally and seal
the test fluid without leakage after subjected to proof pressure test. This test shall be repeated at
275°F ± 5°F for five (5) minutes for qualification inspection and repeated at room temperature
for 1 minute for conformance inspection specified in table VI.
4.8.11 Surge flow. The coupling shall be subjected to a flow at five times the rated flow
for 5 seconds minimum in each direction. This surge flow pattern shall be repeated 100 times.
There shall be no evidence of flow blockage or internal damage and the disconnected halves
shall pass the leakage test (see 4.8.5).
4.8.12 Impulse and vibration (1000 and 3000 psi). The couplings shall withstand the
following tests without evidence of failure.
4.8.12.1 Resonance search. The connected fluid-filled coupling shall be tested for
resonance in a direction parallel and a direction perpendicular to the axis of the coupling. The
frequency and double amplitude shall be slowly varied to within +0 and -10 percent of that
specified for vibration tests as shown on figure 2. All resonant frequencies shall be noted.
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