ASTM D4305 Test Method for Filter Flow of Aviation Fuels at Low Temperatures
4. Summary of Test Method
4.1 A 5-mL specimen of fuel is subjected to a programmed temperature cycle while a pump maintains an oscillating flow at constant rate across a metal mesh test filter. As the temperature falls, separated wax tends to restrict the test filter causing an increase in pressure. When this pressure exceeds 1.33 kPa for more than 0.95 s, the no-flow point is indicated and the cooling cycle is stopped. The pump continues to operate and exert pressure as the fuel specimen is warmed. At the point when the test filter is unplugged and pressure falls below 1.33 kPa for more than 0.95 s, the flow point is indicated and the temperature of the specimen displayed and held.
5. Significance and Use
5.1 The lowest temperature at which aviation fuels remain free of solid hydrocarbon crystals, which may restrict the flow of fuel through filters in an aircraft fuel system, is a key safety parameter in the specification and use of fuels. In Test Method D2386, the freezing point is defined as the temperature at which all crystals disappear following a cooling and warming cycle. In this test method, a cooling and warming cycle is also employed, however, the test result is defined as the flow point, which is the temperature of the specimen at which a test filter becomes unblocked on warming.
