MIL-DTL-5508C
hour (approximately 10 drops per hour) at any pressure over 150 psi to the rated pressure. For
qualification tests the fuse shall be tested at pressures of 40 psi, 80 psi, 150 psi, 50 percent of the
rated pressure, and 100 percent of the rated pressure. For acceptance tests, each fuse shall be
tested at 40 psi and the rated pressure.
4.5.4 Volumetric capacity. The fuse shall be installed in accordance with figure 1.
4.5.4.1 Qualification tests. Qualification tests for volumetric capacity shall be conducted
with unrestricted flow and at the rated pressure as follows:
a. Flow shall be passed through the fuse at 1/10 gallon per minute (gpm), and the
volume of fluid passed through the fuse before the fuse closes shall be measured. For fuses
requiring reverse flow for resetting, the flow shall be reversed. The volume of fluid passed shall
be within the limits specified in figure 2.
b. The test shall be repeated for the percentages of rated flow and the volume of fluid
passed shall be within the limits specified in figure 2.
c. An eight-hour test shall be conducted to verify that the fuse shall not close at flow
rates less than 0.02 gpm.
4.5.4.2 Acceptance tests. All fuses shall be tested at flows of 1/4 gpm and 200 percent
of the rated flow. The volume of fluid passed shall be within the limits specified in figure 2.
These tests for volumetric capacity shall be conducted within unrestricted flow.
4.5.4.3 Volumetric capacity of fuses. The rated volumetric capacity of fuses shall be 10,
20, 40, 60, 80, 120, 160, 200, and 250 cubic inches as applicable. The tube size shall be 1/2 inch.
4.5.5 Immersion. Fuses containing non-metallic parts shall be subjected to immersion tests.
4.5.5.1 Water immersion. The sample shall be immersed in water at 77 °F ± 4 °F
(25 °C ± 2 °C) until the maximum rate of dimensional changes does not exceed 0.0003 inch in a
10-day period as shown by a faired curve plot of measurements. This test shall cover a period of
not less than 30 days. Dimensional measurements shall be made daily for the first 14 days and at
least every 2 days for the remainder of the period. If the unit is made of several non-metallic
parts, of which some remain stationary during operation of the unit, the immersion test shall be
conducted in such a manner that the swelling action will produce the worst possible conditions
towards malfunctioning of the unit.
4.5.5.2 Oil immersion. The sample shall be immersed in hydraulic fluid conforming to
MIL-PRF-5606 at 158 °F ± 2 °F (70 °C ± 1 °C) for a period of 30 days. The oil immersion shall
be subject to the same conditions as the water immersions (see 4.5.5.1) and measurements shall
be made at similar periods of immersion.
4.5.6 Pressure drop. With the apparatus set up as shown in figure 3, the pressure flow
shall be measured on both the closing and resetting directions with unrestricted flow in the
circuit and with a flow restricted to obtain normal working pressure in the fuse. Pressure drop
shall be determined at flow rates of 25 percent, 50 percent, 100 percent, and 200 percent of the
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