MIL-DTL-25427B
inspection (see 4.5) specified herein. All internal parts of the coupling shall be in contact with
the fluid during immersion. After the 72-hour soak period, the coupling shall be subjected to the
next test immediately or remain in the fluid at normal room temperature until such test is
available.
4.8.4 Air inclusion. The coupling shall be subjected to an air inclusion test to determine
compliance with 3.7.4. This test shall be performed during the manual operation test specified in
4.8.2.
4.8.5 Leakage.
4.8.5.1 Leakage at low pressure. The connected coupling and the disconnected halves
shall be subjected to an internal pressure equal to a 30-inch static pressure of hydraulic fluid for
12 minutes. All external surfaces shall be dry at the beginning of this test. There shall be no
evidence of external leakage from the connected coupling. A waiting period of 2 minutes shall
be allowed for leakage rate to become constant from the disconnected halves. Following this
waiting period, leakage shall be measured for the next 10 minutes and shall not exceed one drop.
For conformance tests, the connected coupling and the disconnected halves shall be subjected to
internal pressure equal to 30 inches of hydraulic fluid for 30 seconds. All external surfaces shall
be dry at the beginning of this test. There shall be no evidence of leakage (zero) from either the
coupled coupling or disconnected halves.
4.8.5.2 Leakage at high pressure. Both the connected coupling and the disconnected
halves shall be subjected to a hydraulic static pressure equal to the applicable operating pressure
for 15 minutes. All external surfaces shall be dry at the beginning of this test. There shall be no
evidence of external leakage from the connected coupling. Leakage from the disconnected
halves shall not exceed a trace (insufficient to form a drop) in 10 minutes. Fluid loss as specified
in table III is not considered to be external leakage.
4.8.6 Pressure drop. Pressure drop through the connected coupling shall be measured at
a flow equal to the rated flow specified in table II. The hydraulic fluid flow shall be accurately
maintained. A manometer or other equally accurate method of differential pressure
measurement (differential pressure gauge) shall be connected across the coupling as shown in
figure 2. The temperature of the fluid shall be maintained at 100 °F ± 5 °F. The pressure drop in
the coupling shall not exceed the value specified in table II.
4.8.7 Vacuum. A vacuum shall be applied to the coupling assembly equivalent to 10
inches of Hg (5 psi). When the correct pressure has been attained, the lines shall close for a
period of 5 minutes, during which time there shall be no change in pressure. Temperature shall
be maintained constant within +2 °F both fluid and ambient during this test.
4.8.8 Extreme temperature functioning. The couplings shall be tested with the following
tests without malfunctioning or leakage in excess of the values specified in 4.8.5.
4.8.8.1 High temperature. After immersion in hydraulic fluid but before uncoupled, the
coupling shall be connected to a 30-inch static pressure of hydraulic fluid and subjected to a
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