MIL-DTL-62265C(AT)
4.9.3 Flow rate determination. The flow rate for the assembly shall be determined in
conjunction with 4.9.6 and shall be as specified in table I (see 3.4.3).
4.9.4 Pressure drop test. To determine conformance compliance to the pressure drop
across a clean filter element, the following procedure, or equivalent, shall be used with the relief
valve blocked. Hydraulic pressure, adjusted to provide rated flow, shall be applied to the filter
element. Pressure shall be monitored on the inlet and outlet sides of the filter. The pressure drop
across the filter element shall be the differences between the inlet and outlet pressure and shall not
exceed that specified in table I.
4.9.5 Dirt capacity test. The hydraulic pressure shall be adjusted to provide rated flow
in accordance with 3.4.3. AC Fine Test Dust shall be injected into the hydraulic fluid at
4 minute intervals in accordance with table II. The differential pressure across the filter element
shall be monitored, and shall not exceed the value specified in table II.
4.9.6 Efficiency test. To determine the efficiency of the filter element, the following
procedure, or equivalent, shall be used:
a. Install the test sample into the test setup (see figure 2) with a contaminant level of
less than 0.0004 g per 2000 mL of fluid.
b. Temperature of the hydraulic fluid shall be 73° ± 18°F.
c. Add a 5 mL slurry containing contaminants specified in table III into the mixing
chamber, and agitate for a minimum of 3 minutes.
d. Apply air pressure to force the fluid containing contaminant through the sample
filter assembly and out of the sampling port at rated flow.
e. Collect the filtrate in a 5000 mL flask.
f. Using a suitable wash bottle, wash 750 mL of prefiltered petroleum ether or
equivalent through the contaminant mixing chamber and the test filter.
g. Collect the fluid in the same flask as the filtrate.
h. A membrane filter 1.85 in. diameter disk, absolute 0.8 µ type AA millipore, or
equivalent, shall be washed with 200 mL of prefiltered petroleum ether or
equivalent, and dried to constant weight at 125°F. The weight shall be accurate
to 0.1 milligram. The disk shall be heated at 125°F for 30 minutes and then
cooled 30 minutes in a desiccator.
i. The weighed filter membrane shall be assembled into a suitable filter holder
assembly and fitted to a 5000 mL vacuum flask connected to a suitable vacuum
(minimum 25 in. of mercury (Hg) vacuum).
j. All collected hydraulic fluid (step g) shall be filtered through the membrane
filter. The 5000 mL flask shall then be washed with 1000 mL of prefiltered
petroleum ether or equivalent. The cleaning fluids from the washed flask shall
also be passed through the membrane filter.
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