FED-STD-791D
temperature is 3C lower then the previous reading. The complete operation of
removal and replacement shall require not more than 3 s. If the oil has not
ceased to flow when its temperature has reached 10C, place the test jar in the
jacket in a second bath maintained at a temperature of -18 to -15C. If the oil
has not ceased to flow when its temperature has reached -7C, place the test jar
in the jacket in a third bath maintained at a temperature of -35 to -32C. For
determinations of very low pour points, additional baths should be maintained
with successively lower temperature differentials of about 17C. In each case
transfer the test jar when the temperature of the oil reaches a point of 28C
above the temperature of the new bath. At no time place the cold test jar
directly in the cooling medium. As soon as the oil in the test jar does not flow
when the jar is tilted, hold the test jar in a horizontal position for exactly 5 s, as
noted by a stop watch or other accurate timing device, and observe carefully. If
the oil shows any movement under these conditions, place the test jar
immediately in the jacket and repeat a test for flow at the next temperature 3C
lower.
c. Continue the test in this manner until a point is reached at which the oil in the
test jar shows no movement when the test jar is held in a horizontal position for
exactly 5 s. Certain lubricating oils tend to move as a whole and should be very
closely observed. Record the reading of the test thermometer at this temperature,
corrected for error if necessary.
6.5 Allow the samples to thaw; and when the cloudiness has barely disappeared
observe and record the color and any evidence of separation.
6.6 When the samples reach room temperature, place them in an oil bath after
removing the thermometers. Heat the bath to 232C and immediately remove the
samples.
6.7 Cork the samples and store them at their respective pour points for 18 to 24 h.
6.8 Remove the samples and allow them to thaw. When cloudiness has barely
disappeared, observe and record the color and any evidence of separation.
6.9 Repeat the last operation when the samples reach room temperature.
6.10 Note the homogeneity and miscibility of the samples.
7. CALCULATIONS
7.1 This section is not applicable to the test procedure.
8. REPORTING
8.1 Report the data on the homogeneity and miscibility test forms.
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