MIL---DTL---51194D(EA)
4.4 Verification methods and procedures .
4.4.1 Material, components , and as s embly. Ve rify by e xa min a tio n o f filte r a n d d ra win gs.
Examination involves inspection of the item using the un- aided eye, tools, gages, or other commer-
cial measuring devices.
4.4.2 Airflow res is tance. T h e a irflo w re sista n ce sh a ll be d e te rmin e d a t th e a irflo w o f 20 cfm.
T h e me a su re d p re ssu re d ro p a cro ss th e p a rticu la te filte r, wh e n co rre cte d to sta n d a rd co n d itio n s
o f 21° C (70° F ) a n d 1 a tm (1013 mba r), sh a ll be n o gre a te r th a n th a t sp e cifie d in 3.2. T h e u p ---
stre a m a n d d o wn ---stre a m sta tic p re ssu re me a su rin g tu be s sh a ll be a s clo se a s p o ssible to th e
filte r a n d sh a ll n o t be o n a se ctio n o f d u ct th a t h a s a ch a n gin g cro ss se ctio n a l a re a . Te st fo r
a irflo w re sista n ce a s fo llo ws:
(a )
Co n n e ct th e filte r to a so u rce o f fo rce d a ir.
(b)
Se t th e flo w o f a ir th ro u gh th e filte r to 20 cfm.
(c)
Re co rd th e ba ro me tric p re ssu re .
(d )
Me a su re a n d re co rd th e a ir stre a m te mp e ra tu re .
(e )
D e te rmin e a n d re co rd th e d iffe re n ce be twe e n u p ---stre a m a n d d o wn stre a m
sta tic p re ssu re .
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 (DP (cal)) using the equation below to correct the
measured airflow resistance to airflow resistance at standard conditions:
DP (cal) = DP (measured) x P (test) x 86.21 ¸ [(492 + 1.8T) 1.768]
where:
D 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).
D 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.
4.4.3 Filtration efficiency. T h e te st a p p a ra tu s u se d to me a su re th e filtra tio n e fficie n cy sh a ll
be ca p a ble o f ma in ta in in g a sta ble co n ce n tra tio n o f a e ro so l with a me a n p a rticle size o f 0.3 mi-
cro n s with a ste a d y flo w th ro u gh th e filte r o f 20 scfm (se e 6.4). T h e te st a p p a ra tu s sh a ll h a ve th e
ca p a bility to d e te rmin e th e co n ce n tra tio n o f a e ro so l bo th u p stre a m a n d d o wn stre a m o f th e fil-
te r with in 0.005% . T h e d o wn stre a m sa mp le p o in t sh a ll be lo ca te d su ch th a t ch a n gin g o f its lo ca -
tio n a cro ss th e d u ctwo rk d o e s n o t ca u se a sign ifica n t ch a n ge in me a su re d co n ce n tra tio n s. T h is
sh a ll be ve rifie d u sin g a filte r with a kn o wn me a su ra ble le a k. T h e filte r sh a ll be p la ce d in th e
te st a p p a ra tu s su ch th a t th e flo w o f a ir co n ta in in g th e ch a lle n ge a e ro so l is in th e d ire ctio n in d i-
ca te d by th e ma rkin g o n th e filte r, a n d th e flo w o f a e ro so lize d a ir sh a ll be ma in ta in e d a t 20± 3
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