MIL-PRF-25478D
4.6.7 Vibration test. The oil cooler shall be installed in a test system with the oil
temperature at 225° ± 2°F, the rated oil flow as specified in the acquisition document (see 6.2),
and the oil inlet pressure at the lowest operating pressure. The oil cooler shall be vibrated along
each of three mutually perpendicular axes through a frequency survey of 25 to 150 Hertz (Hz) in
order to determine the existence of resonant frequencies. If a resonant frequency is found, the oil
cooler shall be vibrated at that frequency. If more than one resonant frequency is observed, the
test frequency should be at the most severe resonant frequency. If no resonance is observed, the
oil cooler shall be vibrated at 150 Hz. The test shall be conducted for 35 hours for each of the
three mutually perpendicular axes, or if using a two-directional vibrator, for 50 hours with the oil
cooler in the horizontal position and 50 hours in the vertical position. The vibration to the oil
cooler shall be maintained at a 10g acceleration. There shall be no leakage, permanent distortion,
or failure of the mounting structure integral to the oil cooler. At the completion of the test, the oil
cooler shall satisfy the requirements of the static pressure test in 4.6.3.
4.6.8 Pressure cycles. The oil cooler shall be completely submerged in oil at 275° ± 5°F
for Type IA and Type IB oil coolers, and at 350° ± 10°F for Type II oil coolers. An air pressure
cycle (3 ± 3 psi to 60 ± 1 psi and back to 3 ± 3 psi) shall be applied to the oil inlet with a cycle
time of 4.5 ± 0.5 seconds with the oil outlet closed. The oil cooler shall be subjected to 50,000
cycles without leakage or permanent distortion. At the completion of the test, the oil cooler shall
satisfy the requirements of the static pressure test in 4.6.3.
4.6.9 Fluid resistance and material compatibility test.
4.6.9.1 High temperature test. The oil specified in the acquisition document (see 6.2)
shall be circulated through the oil cooler for 96 hours at a temperature of 275° ± 5°F for Type IA
and Type IB oil coolers, and 24 hours at a temperature of 350° ± 10°F for Type II oil coolers.
Following this the oil cooler shall be subjected to the static pressure test in 4.6.3, except that the
test pressures shall be 1 psi, 50 psi, and 100 psi. The pressure shall be held for 30 seconds during
each test. The high temperature test shall be repeated 7 times. There shall be no leakage.
4.6.9.2 Low temperature test. Following the high temperature test, the oil cooler shall be
soaked for 72 hours at -65° ± 5°F while filled with the oil specified in the acquisition document
(see 6.2). The oil cooler shall be subjected to the static pressure test in 4.6.3 at -65° ± 5°F except
that the pressures shall be 1 psi, 50 psi, and 100 psi alternately for at least 10 times. The pressure
shall be held for 30 seconds during each test. There shall be no leakage.
4.6.10 Temperature control and surge protection device test. The requirements of the
temperature control and surge protection devices shall be demonstrated using the test methods of
MIL-PRF-5636.
4.6.11 Salt fog. The oil cooler shall be subjected to the salt fog test in ASTM B117 for
50 hours. The oil cooler shall then be subjected to the individual tests in 4.3.1.
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