ASTM D4539 Test Method for Filterability of Diesel Fuels by Low-Temperature Flow Test (LTFT)
7. Procedure
7.1 Filter a fresh specimen of test fuel (Warning - Combustible liquid. See A2.3) at 15°C or higher, through dry, lintless filter paper, having a nominal filtration rating of less than 17 µm.
7.2 Clean and inspect the filter assembly before each test. Filters shall be standardized before initial use and after every 20 tests as specified in Annex A1.
7.2.1 Clean the assembled filter with two solvents using a vacuum to draw the solvents through the screen. Begin with three successive washes of at least 50 mL of heptane (Warning - Flammable. See A2.2), followed by three successive washes of at least 50 mL of acetone (Warning - Extremely flammable. See A2.1). Air dry the filters after washing.
7.2.2 Visually inspect each filter assembly for screen damage or the presence of particulates. Discard any damaged filter screens. Reclean and standardize any filter screens containing particulates.
7.3 Pour 200 mL of clean, dry fuel (Warning - Combustible liquid. See A2.3) into each of the several 300-mL beakers.
7.4 Insert a clean standardized filter assembly into each specimen container and tightly cover the joint (Point A of Fig. 1) and lid with aluminum foil to exclude condensation.
7.5 Insert a total immersion thermometer into one or more separate, identical glass specimen bottles or beaker(s) containing 200 mL of Jet A aviation turbine fuel kerosine, or Grade No. 1 (or Grade Low Sulfur No. 1) (Warning - Combustible liquid. See A2.3) or equivalent liquid that will not phase separate at temperatures down to -30°C. The thermometer bulb should be positioned in the center of the bottle or beaker approximately half way between the top and the bottom of the liquid.
7.6 Place the specimen bottles or beaker (from 7.3 through 7.5) into the cooling bath at a temperature that is at least 5°C above the wax appearance point (Test Method D3117) or cloud point (Test Method D2500) of the fuel under test. During multiple specimen testing, a sufficient number of temperature monitoring vessels (from 7.5) must be distributed throughout the cooling bath to insure all test specimen temperatures conform with precision requirements. The positioning of all bottles or beakers shall permit unimpeded circulation of the cooling medium across their bottoms and sides.
7.7 Close the cooling bath’s door, if it has one.
7.8 Start the temperature programmer at a rate of -1.0°C/h.
7.9 Before the sample reaches the desired test temperature, check the following:
7.9.1 Apply the pinch clamp at Point B (Fig. 1).
7.9.2 Place an empty receiver vessel in position.
7.9.3 Adjust the vacuum to 20.0 kPa +/- 0.2 kPa (150 + 1.5 mmHg) (Warning - Mercury is a poison. See A2.4) below atmospheric pressure.
7.9.4 Reset the timer.
7.10 When the specimen has cooled to the desired testing temperature, use the filter assembly stem to gently stir (15 revolutions at approximately 1 turn/s) the specimen to disperse any settled wax crystals. Remove the aluminum foil and connect the filtration apparatus joint at Point A (Fig. 1). If the specimen has to be removed from the cooling bath for filtration, these steps shall be completed within 1 min.
7.11 Filter the specimen by removing the pinch clamp at Point B (Fig. 1) while simultaneously starting the timer. If necessary, adjust the vacuum system to maintain a vacuum of 20.0 kPa + 0.2 kPa (150 + 1.5 mmHg). (Warning - Mercury is a poison. See A2.4) below atmospheric pressure.
7.12 Reapply the pinch clamp at Point B (Fig. 1) at precisely 60 s or when suction is lost, whichever occurs first. Record the volume of specimen filtered in millilitres and the testing temperature in degrees Celsius.
7.13 Pass-Fail Criteria:
7.13.1 Passing Result - The result is considered a pass if most of the specimen has been siphoned into the receiver vessel within 60 s, and suction is lost due to the low level of specimen remaining in the specimen vessel.
NOTE 2 - Typically, a volume of approximately 180 mL will be collected in the receiver vessel in a passing result, but this volume may vary due to differences in specimen vessel dimensions and the temperature/volume characteristics of the fuel.
7.13.2 Failing Result - The result is considered a fail if suction is not lost within 60 s.
7.14 To determine the minimum LTFT pass temperature, repeat 7.9 through 7.12 on subsequent test specimens that have been cooled 1°C lower than the previous test temperature, until at least one passing result and one failing result are obtained (see 7.13.1 and 7.13.2).
7.15 Alternatively, cool a single specimen to a desired temperature and determine whether a passing (7.13.1) or a failing (7.13.2) result is obtained.
