FED-STD-791 Lubricants, Liquid Fuels, And Related Products, Testing Method OfThis test method standard is composed of standard test methods for sampling, inspecting and testing lubricants, liquid fuels and related products. It is issued pursuant to the Federal Property and Administration Services Act of 1949, as amended and its application to the purchase of commodities referred to herein is mandatory on all Federal agencies.

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'�NOTE:This draft dated 15 April 2006' by DasH - Page 170 of 460

FED-STD-791D

from the storage area, place them in a centrifuge, and operate the centrifuge at 500 " 25 rpm for

30 " 1 min. If the residue is a solid, wash it several times with naphtha, a sufficient number of

times to assure that it is free of oil.

6.8 Remove the centrifuge tubes for the centrifuge and decant and discard the

supernatant oil. Permit the centrifuge tubes to drain in an upside down position at 25� " 3�C for

a period of 2 h.

If the separated material in not sufficiently compacted by the centrifuging to

NOTE 3:

permit decanting the supernatant oil, continue the centrifuging for 5-minute

intervals until decanting is possible. If the material is a liquid at the conclusion of

the 30-minute centrifuging period, or if it cannot be compacted, cork the

centrifuge tube and replace them in storage for an additional 30 days. At the end

of the second storage period, proceed as directed in paragraph 6.7. If there is no

visual liquid or solid residue after 30 days, stop the procedure and report zero

residue.

6.9 Place the centrifuge tubes in an upright position in an oven controlled at 05� " 3�C

for approximately 2 h.

6.10 Remove the centrifuge tubes from the oven and place them in a desiccator to cool to

25� " 3�C. Weigh the tubes and contents to the nearest mg. Subtract the weight of the empty

centrifuge tubes to determine the weight of the separated material.

6.11 If the residue remains a liquid at the end of the second 30-day storage period,

centrifuge the tubes as specified in 6.7. Remove the tubes from the centrifuge and note the

volume of the separated liquids to the nearest 0.05 mL.

7. CALCULATIONS

7.1 Calculate the percent insoluble residue in the sample from the formula:

Average amount of separated residue (grams) the three centrifuge tu

Percent insoluble residue =

0.9 * weight percent of additive in sample

where:

0.9 = assumed specific gravity of the sample:

NOTE 4: The weight percent of additive in the sample can be obtained from the manufacturer

of the sample.

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