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|  MIL-F-27656C(USAF)
microscope. There shall be no migration traceable to the element or its packaging. After this test, the
filter shall successfully withstand the test specified in paragraph 4.6.6.1.
4.6.7. Pressure inpulse tests.
4.6.7.1 Filter housing test. The falter housing shall be subjected to 100,000 impulse cycles at 160 F.
Each impulse cycle shall consist of a pressure rise from operating pressure (Type I), or a pressure
less than 100 psi (Type II), to a peak surge pressure of 1.331
tunes the rated operating pressure,
as shown by an oscilloscope. The impulse time (duration of impulse) shall not be longer than 0.05
seconds and the rate of pressure rise shall be a minimum of 50,000 psi per second. Cycling shall be
performed at a maximum rate of 300 cycles per minute. The differential pressure indicator shall not
actuate during the impulse test There shall be no evidence of external leakage or structural failure
during this test.
4.6.7.2 Filter element test. The filter element impulse test shall be run simultaneously with the housing
impulse test. Noncleanable elements shall withstand 10,000 impulse cycles without evidence of structural
failure. Cleanable elements shall withstand 100,000 cycles without evidence of structural failure.
4.6.8 Flow fatigue test.
4.6.8.1 Initial bubble point. Elements to be submitted for flow fatigue tests shall be subjected to the test
m paragraph 4.6.6.1 to establish an initial bubble point pressure.
4.6.8.2 Filter element test. Filter elements shall be installed m the housing and subjected to 3,000 psi
relet pressure and rated flow with fluid at 160F. Elements shall be loaded with AC fine test dust and
glass beads to produce the specified differential pressure across the housing relet and outlet. Elements
or parts of elements that are designed to withstand 0 to 150 psi differential pressure in accordance with
paragraph 37.2.4a shall withstand series I tests only. Elements or parts of elements that are designed to
withstand 150 to 5,000 psi differential pressure in accordance with paragraph 3.7.2.4b shall withstand
series II tests only. A cycle shall consist of increasing the differential pressure across the filter unit
from 0 to the values specified and back to 0 by first increasing then decreasing flow through the
filter unit. The cycling rate shall not exceed 300 cycles per minute The number of cycles at each
differential pressure shall be as follows
Series 1
a
3,000 cycles at 55 psi pressure drop.
6,000 cycles at 75 psi pressure drop
b.
1,000 cycles at 100 psi pressure drop.
c.
Series II
40,000 cycles at 75 psi pressure drop.
a.
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