MIL --- DTL --- 51222E(EA)
4.4 Tests. Filters shall be tested in the following sequence:
4.4.1 Air flow resistance. The pressure drop across the filter shall be determined at the rated
air flow of 150 scfm. The upstream and down --- stream static pressure measuring tubes shall be
as close as possible to the filter and shall not be on a section of duct that has a changing cross
sectional area. Test for air flow resistance as follows:
(a) Connect the filter to a source of forced air.
(b) Set the flow of air through the filter to 150 scfm
.
(c) Record the barometric pressure.
(d) Measure and record the air stream temperature.
(e) Determine and record the difference in static pressure head up --- stream of the filter
to that down --- stream of the filter. NOTE: If barometric pressure and air stream temperature
are not within 760±8 mm and 70±2_F, calculate the correction factor below to correct the mea-
sured pressure drop across filter to standard conditions (1 atm and 70_F). If barometric pres-
sure and air stream temperature are within 760±8 mm and 70±2_F, a correction factor of unity
may be assumed.
ΔP(cal) = ΔP(measured) x CF, where
CF = P(test) x 86.2
1.768
(460 + T)
Notes:
CF --- Correction factor
ΔP(cal) --- Air flow resistance corrected to standard conditions in inches of water gage
(iwg)
P(test) --- Barometric pressure at time of test in mm Hg
ΔP(measured) --- pressure drop recorded from test measurement (iwg)
T
--- Temperature of air stream flowing through filter in degrees F
4.4.2 Leakage. Rigidly position the filter to be tested with the long axis in the vertical posi-
tion. Connect the filter to a source of forced air and place a mixing chamber at the influent side
of the filter. Regulate the flow of air from the blower to 1/5 the rated airflow of the filter (30
scfm). Introduce R --- 134a into the intake of the blower; monitor and maintain a concentration
of 1000 ppm by volume of R --- 134a in airflow of 30 scfm on the influent side of the filter at
75 ± 10_ F and Relative Humidity (RH) no higher than 50 percent. Leakage shall be deter-
mined using a suitable leak detector (see 6.7) for sampling and detecting R --- 134a at the efflu-
ent side of the filter. Purge the filter by passing fresh air in the reverse direction of that
indicated above through the filter at 150 scfm for 1 minute. Keep the exposure of the filter to
air to a minimum. The airflow time for leakage should not exceed 3 minutes.
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