Air release is a test where air is blown through a lubricating fluid at a set temperature and pressure. The release of the ‘trapped’ air bubbles within the fluid is measured until no additional gas escapes. The time it takes to reach this point is called the air release and time is measured in minutes.
Tested On: Hydraulics, Compressors, Steam and Gas Turbines
Diagnostic significance: The air release should be as low as possible. Contamination and oxidation products can increase the air release time. Air is a poor lubricant and so if air is likely to become trapped for long periods in the lubricant the lubricant becomes less effective. In hydraulic applications the entrainment of air in a system poses many risks:-
- Air can be compressed and this can lead to potential uncontrolled movement in machinery.
- Air when compressed becomes very hot and can actual lead to thermal breakdown of the oil surrounding the bubbles. The principle is very similar to the combustion process in a diesel engine but instead of a hydrocarbon fuel being passed into air and then compressed, air is passed into a hydrocarbon fluid and then compressed.
Typical Diagnostic limit: 5 to 20. Typically ~10 minutes