F-F-351F
4.6.5 Filtering ability.
4.6.5.1 Filtering ability for type I and II filters and type IV, classes 1-3 filter elements. To
determine conformance to 3.5.5, a type I or a type II filter, or a type IV, class 1-3 filter element,
assembled in a filter body for which the filter element is intended, shall be tested for filtering ability
by use of a testing apparatus consisting of an oil reservoir with oil level indicator, and a suitable oil
circulating system provided with oil pressure and temperature indicators and controls. The
capacity for the type I or type II filter of this system, exclusive of the filter under test and
dependent on the filter or element type, shall be adequate for the quantities specified in tables VIII
and IX, plus the contaminant added during a 22 hour period. A device shall be provided for
adding contaminant to the oil in the reservoir. The addition shall be made in small, drop-sized
increments at a substantially uniform rate. A weighed quantity of contaminant, appropriate for the
add period employed, which has been conditioned in an agitator for at least one hour, shall be
blended at 30 psi pressure for 30 minutes with oil taken from the filter test system in preparation
for charging the quadrant. The blending process is started 30 minutes before the quadrant is ready
for its charge. Quadrant add periods of 4 or 5 hours are recommended for test periods. Longer
add periods may be used, provided continuous mixing system is employed to keep the contaminant
mixed. Additional test conditions and procedure shall be as specified in tables VIII and IX.
Curves of pressure drop and normal pentane insolubles shall be plotted versus hours of operation.
Smooth curves shall be faired through the plotted data points. The contractor's Government
approved inspection plan shall include a procedure for filtering ability that uses the restrictions and
methods of determination shown in tables VIII and IX for the filter types indicated.
TABLE VIII. Filtering ability test conditions and procedure for
type I filters and type II filter elements.
Oil at filter inlet
Test oil
Contaminant
Rate of
Total
Oil
Filter
solids
hours of
sample
Effic.
Quantity
addition
filter
to be
(%
Temp
Pressure
Quarts
grams/
operation
analyzed
min.)
°F (°C)
Class
psi (kPa)
Type
(Liters)
Designation
hour
1/
2/
4/
30 + 1
Mineral
5 (4.7)
SOFTC-2A
2.2
88
Normal
85
1
180 + 5
(82 ± 3)
(206 ± 11)
plus
3
180 + 5
30 + 1
Additive
Sufficient
SOFTC-2A
4.4
88
Pentane
85
oil to fill
insolubles
assembly
3/
1/ To be accumulated in successive units of 22 hour periods of continuous filter operation and
contaminant addition, separated by 2 hour shutdown periods during which the oil bypasses
the filter completely and no contaminant is added.
2/ Immediately after each 22 hour period, oil shall be withdrawn from the system to reestablish
the initial oil level in the reservoir. The portion of oil so withdrawn shall constitute the
sample for analysis.
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