D6468_08(2013)_11
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Adjust the heating bath
to a temperature of 150
plus or minus 1.5
degrees Celsius.
See 6.3 of the written standard.
Assemble the filter apparatus
with a new filter paper.
Filter at least 100
milliliters of the fuel sample
through the paper.
Use the inline vacuum regulator
so that the maximum vacuum
is 27 kilo-pascals 200
millimeters mercury.
Measure 250 plus or minus
2 milliliter volumes
of filtered fuel.
And decant into each
of two aging tubes.
See appendix X.3 of
the written standard.
Where practical,
filter a fuel sample
larger than 100 milliliters.
This will reduce the
possibility that the paper
may absorb trace materials
that affect stability.
Place the uncapped sample
tubes in the heating bath,
making sure the level of
the fluid in the test tube
is below the surface of the
oil in the heating bath.
Age the fuel sample for 90
plus or minus 3 minutes,
or 180 plus or minus 5 minutes.
Place the tubes in the bath in
the same order in which they
are to be removed.
Warning-- fuels will be heated
above their flash points.
There is a possibility
that certain light fuels,
such as kerosene, will boil
under conditions of the test.
Both situations raise
the risk of fire
when an ignition
source is present.
Fuel samples that
may contain gasoline
or other volatile components
should not be tested.
The severity of the
test is increased
by aging for longer times
at 150 degrees Celsius.
The selection of the aging
time depends on application,
and should be established by
correlation with other tests
or with application
requirements.
Remove the sample
from the heating bath
and allow to cool gradually
in air to 20 to 25 degrees
Celsius, over a period of
90 minutes to four hours.
Cool in the dark to prevent
photochemical reactions.
Do not accelerate cooling
by immersing in a cooling
bath, as this can result in
small particle size and a lower
pad rating.
If samples are allowed to
stand more than four hours
before filtering,
insoluble gum may
adhere to the aging tubes
resulting in erratic data.
Warning-- the hot samples
can cause severe burns.
Use protective equipment.
Prepare a filtration assembly
with a new filter paper,
and attach all grounding
clips to ground.
Filter one of the two
aged fuel samples.
While maintaining vacuum,
wash the aging tube
with three small portions,
about 15 millimeters each,
of isooctane.
And filter through
the filter paper.
Wash the inside of the filter
assembly with isooctane,
and remove the funnel
portion of the assembly.
While still maintaining
vacuum, use a gentle stream
of isooctane from
a squeeze bottle
to wash the filter clean
of any traces of fuel oil,
and allow it to dry under
vacuum for one or two minutes.
See note 13 of the
written standard.
Shutoff vacuum and
remove the filter
from the assembly with forceps.
If the deposit on the filter
pad is not evenly distributed,
reject the pad
and rerun the test
after cleaning the
membrane filter holder.
See 9.2 of the written standard.
When multiple tests are carried
out, the margin of the pad
may be used for
sample identification.
Some laboratories may
contain sufficient airborne
contamination to change results
if the air drying period
is prolonged.
If the deposit on the filter
pad is not evenly distributed,
reject the pad and
rerun the test.
See 9.2 of the written standard.
Place the test filter
on the stack of at least
10 unused filter pads.
Center the search
unit on the filter,
and record the meter value
as percent reflectance
filter pad rating to
one decimal place.
Repeat 11.5 through
11.8 of the written
standard using the second
of two aged fuel samples.