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 your compressor.