The ASTM D-1401 Demulsibility Test
The demulsibility test is used to determine the separation
characteristics of oil in water for both synthetic oil and petroleum based
fluids. The test as defined by ASTM calls for a mixture of oil and water
at a specified temperature. 40 mL of air compressor oil is mixed with a
special stirrer designed to spin at 1500 rpm at 40 degrees Celsius with 40ML of
distilled water in a graduated cylinder. The amount of oil, water and emulsion
is recorded every 5 minutes for an hour. For compressor oil above 90
cSt at 40C, it is recommended that the testing temperature be raised to 82
degrees C. If after one hour, separation of the emulsion does not occur,
the test should be ended.
For petroleum based oil, the oil will normally float on top of the water.
Due to the high specific gravity of synthetic compressor oil, the water will
float to the top of the test cylinder. this has no effect on the overall
effectiveness of the test procedure. For oils with very high viscosities
that are difficult to mix into an air/oil emulsion, the ASTM D-2711 test
procedure should be followed.
The importance of oil demulsibility for air compressors is critical,
especially in areas of the country with high humidity. With proper
dumulsification properties, an oil will be able to remove the water form the oil
system in the oil water separator, which will translate into longer life for