MIL-PRF-83870C
bubble point test in 4.6.2.1.
4.6.7 Flow fatigue. The filter element shall be installed in a non-bypass type test filter housing, placed in a test
system and subjected to fatigue cycles with the test fluid at table II temperature and flow rate. The cycling rate and
the number of fatigue cycles at each differential pressure are specified in table II. There shall be no evidence of
damage as indicated by performing the bubble point test in 4.6.2.1 (to verify that the bubble point has decreased by
no more than 10%) and by satisfactory completion of the media migration test in 4.6.8.
4.6.8 Media migration. The filter element shall be placed in a test filter housing and then this assembly shall be
mounted in the normal position (bowl at bottom) on a vibration test stand. The filter assembly shall be filled to the top of
the filter element with pre-cleaned test fluid (see 4.4.1.1), capped at both inlet and outlet ports, and soaked at 350°±
5°F for 100 hours. The filter assembly shall then be cooled to 70° to 90°F and subjected to a sinusoidal vibration test in
three mutually perpendicular axes. The rate of change of frequency shall be logarithmic.
4.6.8.1 Resonance search. Determine filter element resonant frequencies by varying the frequency of applied
vibration as specified in part 1 of table V. Repeat the resonance search for each of the three axes.
TABLE V. Vibration data
Part
Vibration level
Frequency band
(double amplitude inch or gravity)
(Hz)
1
0.1 inch
5 to 14
1.0g
14 to 23
0.036 inch
23 to 74
10.0g
74 to 2,000
2
0.1 inch
5 to 14
1.0g
14 to 23
0.06 inch
23 to 104
20.0g
104 to 2,000
4.6.8.2 Resonance dwell. The filter assembly shall be vibrated along each axis at the four most severe resonant
frequencies for 30 minutes at each resonance. Vibration levels are given in part 1 of table V and vibration times are
given in part 1 of table VI. If a new resonant frequency occurs during this test, adjust the vibration frequency to maintain
peak resonance.
TABLE VI. Vibration schedule
Part
Total vibration time at resonance
Number of resonances
(min)
1
0
0
30
1
60
2
90
3
120
4
2
30 minutes cycling per axis
0
10
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