MIL-DTL-24694A(SH)
4.6.5.2 Variable frequency. The valves shall be vibrated from 4 (or lowest obtainable frequency) to 2000 hertz
at the amplitude specified in table II. From 4 to 50 hertz, the valves shall be vibrated in discrete frequency intervals
of 1 hertz for 1 minute minimum at each frequency. From 50 to 2000 hertz, a logarithmic ascending and descending
sweep of not less than 20 minutes total shall be conducted.
4.6.5.3 Resonance dwell. Test valves shall be vibrated along each axis at the most severe resonant frequencies
determined in 4.6.5.1 at the amplitudes specified in table II. The dwell test time shall be divided equally between
the significant resonant frequencies. If more than four significant resonant frequencies are found for any one axis,
the four most severe resonant frequencies shall be chosen for the dwell test. Total test time shall be 2 hours for each
axis. If no resonant frequencies are identified, the valve shall be tested at 50 hertz.
TABLE II. Vibratory displacement, single amplitude.
Table amplitude 1/
Frequency range
(Hz)
(mm - minimum)
(inches - minimum)
4 to 15
1.25
0.05
16 to 25
1.00
0.04
26 to 33
0.75
0.03
34 to 40
0.50
0.02
41 to 50
0.25
0.01
51 to 2000
0.25
0.01
NOTE:
1/
For Government-conducted tests, the maximum amplitude
shall not exceed the minimum required amplitude by more
than 20 percent.
4.6.6 Shock. The valve shall be subjected to high-impact mechanical shock tests in accordance with the
requirements for Grade A, Class I, lightweight, Type B, fixture 4A of MIL-S-901. A valve shall be considered to
have failed the shock test if it does not meet the leakage test of 4.6.3.3, or shows any signs of external or internal
damage when examined in accordance with 4.6.1. The valve shall be pressurized to a setting not less than
75 percent of its maximum set pressure during shock testing.
4.6.7 Endurance. The valve shall be subjected to 100,000 cycles while set at the highest pressure setting for
the class or group of classes. Each cycle shall consist of imposing rated flow through the valve and then reducing
the pressure to zero. Cycling shall be accomplished at a rate not to exceed 60 cycles per minute. Fluid temperature
shall be maintained at not less than 40 °C (104 °F). Leakage at the reseat pressure determined in 4.6.3.2 shall be not
greater than two times the allowable reseat leakage identified in the applicable specification sheet.
4.6.8 Operating temperature.
4.6.8.1 Low temperature. Unless otherwise specified (see 3.1), the fluid for this test shall be in accordance
with MIL-PRF-83282. The test setup shall include a handpump or power driven pump that shall provide a flow of
not less than 1 liter (¼ gal) per minute to the relief valve. The test shall be conducted on two valves, one adjusted to
the lowest setting of the lowest pressure range tested and one adjusted to the highest setting of the highest pressure
range tested. The pump shall be operated at room temperature at not less than the minimum flow rate. The highest
pressure developed at the relief valve inlet shall be noted. Unless otherwise specified (see 3.1), the test setup shall
then be maintained at a temperature not warmer than -29 °C (-20 °F) for 2 hours with the valve unpressurized. The
valve shall then be pressurized to 75 percent of the set pressure and the low temperature maintained for 2 additional
hours. The pump shall then be operated at the same rate as at room temperature and the highest pressure noted. The
pressure value obtained at -29 °C (-20 °F) shall not vary more than ±10 percent from those obtained during the room
temperature test.
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