MIL-PRF-83870C
(4.6.5), pressure buildup and collapse (4.6.6), and flow fatigue (4.6.7) tests.
4.6.4 Efficiency. The efficiency for filter elements is computed as specified in 4.6.4.1 and shall meet the contaminant
removal by weight specified in the efficiency test in table II.
4.6.4.1 Efficiency computation.
A- (B - C)
Efficiency = __________________ x 100 (1)
A
where:
A = add value
B = contaminant value
C = blank value
4.6.4.2 Contaminant value (B). The filter element shall be installed in a test filter housing and placed in a test system
which has been previously flushed with pre-cleaned test fluid (see 4.4.1.1) (a typical test system is shown in figure 11).
Test fluid (2,000 mL) shall be added to the test system. Then, a slurry containing the add value of contaminants shown
in table II shall be mixed with the test fluid. The test fluid, at the rated flow specified in table II, shall be passed through
the filter element and then through a previously cleaned and weighed 0.8 micron absolute filter membrane (see 6.6).
The test fluid shall be collected and the filter membrane weighed. The difference in weight between the filter
membrane before and after this procedure is the weight of contaminant passing through the filter element and is the
contaminant value (B) in equation 1.
4.6.4.3 Add value (A). A free-flow dummy element shall be installed in a test filter housing and the procedure in
4.6.4.2 shall be repeated four times. The add value (A) in equation 1 is the average of the weights of contaminant
collected in the four runs. The weight of the contaminant collected in each of the four runs shall be 95% or more of the
weight of the contaminant added.
4.6.4.4 Blank value (C). The filter element shall be installed in a test filter housing and, with no contaminant added,
the procedure in 4.6.4.2 shall be repeated. The weight of contaminant collected is the blank value (C) in equation 1.
The blank value is the weight of contaminant attributed to the test system and filter element and shall be less than
0.0007 gram.
4.6.4.5 Multi-pass efficiency testing. If required, multi-pass efficiency testing, in accordance with ISO 4572, will be
performed (see 6.2 and 6.3.1).
4.6.5 Maximum particle passed. The maximum particle passed is determined by following the procedure in 4.6.4.2 using
the add value of contaminant specified in table II. The element with the lowest initial bubble point shall be used in this
test. The largest particle size passed shall be no greater than the value specified in table II.
4.6.6 Pressure buildup and collapse. The filter element with the highest initial bubble point shall be installed in a test
filter housing and placed in a test system filled with test fluid pre-cleaned in accordance with 4.4.1.1 (a typical test
system is shown in figure 12). The rated flow shown in table II shall be maintained during this test. The clean-up filter
shall be bypassed during this test. The pressure drop across the clean element shall be measured to verify that the
clean element pressure drop does not exceed the value in table II. Add AC dust, in slurry, Through the dust valve in the
incremental amounts specified in table II at 4 minute intervals. When the minimum AC dust in table II is added, the
element pressure drop in table II shall not be exceeded. Additional AC dust shall be added until the minimum collapse
pressure in table II is obtained. There shall be no sign of structural failure indicated through a visual inspection and the
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