The RBOT test for determining Oxidative Stability

The Rotating Bomb Oxidation Test, also known as RBOT, is used to determine the oxidation stability of an air compressor oil by subjecting the oil to extreme oxidation conditions.  This test is normally measured by ASTM D-2272, as defined my the American Society of Mechanical Engineers. The oil is put in a vessel, or bomb, where it is subjected to oxygen under pressure in the presence of a copper catalyst and submerged in 150 C water and rotated axially at 100 rpm, which causes a rise in the vessel pressure.  As oxidation occurs in the vessel, the pressure increases.  The time is then recorded until the pressure drops 25 psi.  The longer it takes the compressor oil to drop 25 psi, the better its oxidation stability.

The RBOT test is very informative as a method to compare different brands of compressor oil, as well as the conditions of used oil.  Caution must be used in applying this test to compare different base stocks of oil, since some oils such as PAO have better oxidation stability than ester base stock oils.  This is why many manufacturers of compressor oil have PAO/ester blends to create a mixture that has some of the benefits of both. 

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