MIL---DTL---52011(EA)
4.4 Tests.
4.4.1 Airflow resistance. The airflow resistance shall be determined at the airflow of 12 cfm.
The measured pressure drop across the particulate filter, when corrected to standard conditions
of 21°C (70°F) and 1 atm (1013 mbar), shall be no greater than that specified in 3.2. The up ---
stream and down --- stream static pressure measuring tubes shall be as close as possible to the fil-
ter and shall not be on a section of duct that has a changing cross sectional area. Test for airflow
resistance as follows:
(a)
Connect the filter to a source of forced air.
(b)
Set the flow of air through the filter to 12 cfm.
(c)
Record the barometric pressure.
(d)
Measure and record the air stream temperature.
(e)
Determine and record the difference between up --- stream and downstream
static pressure.
If the recorded air stream temperature and barometric pressure is different than 21°C (70°F) and 1
atm, calculate and record the air flow resistance (ĆP (cal)) using the equation below to correct the
measured airflow resistance to airflow resistance at standard conditions:
ĆP (cal) = ĆP (measured) x P (test) x 86.21 ÷ [(492 + 1.8T) 1.768]
where:
Ć P (cal) air flow resistance corrected to standard conditions in millimeters of water
gage (mm wg).
P (test) barometric pressure at time of test in millimeters of mercury (mm Hg).
Ć P (measured) air flow resistance from test measurement in millimeters of water.
T temperature of air stream flowing through the filter in degrees C.
Note: Correction for nonstandard conditions is not required when it is clear that the passage or
failure of the filter is not in doubt.
4.4.2 Air leakage. The sample filters shall be tested for leakage using a test apparatus which
shall have two flat (within .005 inch) smooth (32 micro inch) surfaced metal plates at least .25
inch thick that can be clamped to the gaskets on the inlet and outlet of the filter. The clamping
mechanism shall be controlled so that the total combined compression of the two gaskets does
not exceed .120 inch. There shall be provisions in one of the plates which shall be fixed to the base
of the apparatus for pressurized air to be introduced into the filter under test through a flow me-
ter capable of measuring a flow of 0.91 + 0.06 cubic inches per minute of air flow. There shall also
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be provisions for measuring the pressure inside the filter between plates through the use of a ma-
nometer or pressure gage capable of measuring pressures of 12.00 inches of water with an accu-
racy of + .06 inches of water. The internal pressure measurement shall be taken through a
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separate passage through one of the two plates from the passage that is used to introduce the
measured flow of air. The apparatus shall also have a flow regulation valve by which the air flow
can be controlled. The test shall be conducted by clamping the filter to be tested between the two
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