MIL-DTL-62337C(AT)
4.8.2 Operating requirements verification.
4.8.2.1 Initial airflow restriction. To determine conformance to 3.4.1, the assembly shall
be subjected to a dust free airflow of 900 ft3/min (425 L/s) through a new filter element. The
restriction to flow shall be measured to verify that the restriction is not greater than 900 ft3/min
(425 L/s). The humidity condition of 3.4 shall not apply.
4.8.2.2 Dust capacity. To determine conformance to 3.4.2, the assembly shall be
mounted in the test setup conforming to figure 2, and 1 hour cycles with stepped flow rates as
specified in table 1 shall be completed. The restriction to flow (pressure drop through the
assembly and absolute filter) shall be measured each time the flow is adjusted to 900 ft 3 /min
(425 L/sec). Coarse dust shall be fed into the inside of the assembly at 0.025± 0.005 g/ft 3 (0.88±
0.18g/m 3) of actual input airflow. The test shall be conducted until the airflow restriction at 900
ft 3 /min (425 L/s) reaches 20 inches of water (5.0 kPa) or 80 hours service life, whichever comes
first (see 3.4). Chemical analysis of the coarse test dust shall be in accordance with ISO 5011.
Particle size distribution shall be in accordance with ISO 5011. The dust injector to be used will
be as specified in ISO 5011. At the end of the test, (1) inspect the clean side of the element and
clean side of housing assembly. Any visual signs of dust tracking shall be cause for rejection,
(2) verify that a minimum coarse dust accumulative efficiency of 99.9% has been achieved, (3)
verify that an 80 hour service life has been achieved at a maximum 20 inches restriction limit at
rated air flow and (4) verify that a pre-cleaner efficiency was not less than 97%. The following
formulas shall be used to determine coarse dust or pre-cleaner efficiency:
W1 - [ (W4 - W5) + (W2 - W3) ]
Precleaner efficiency (%) =
x 100
W1
W1 - (W2 - W3)
Coarse dust efficiency (%) =
x 100
W1
Where:
W1 =
Weight of coarse dust fed into the assembly.
W2 =
Weight of absolute filter element and its entrapped dust.
W3 =
Weight of absolute filter element at start of test.
W4 =
Weight of filter element, its entrapped dust and dust encasing the sides of the
filter housing compartment.
W5 =
Weight of filter element at start of test.
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