D6468_08(2013)_11

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.