Air release properties

The air release time is defined as the time in minutes after the air dispersed in oil has been removed again until 0.2% vol. remains. Air at a set pressure level is blown into the oil through a fixed nozzle over a set period of time.

Using the density, the dispersed air bubbles' escape from the oil is then tracked over time and recorded on a graph until the volume stays constant. The air release time is extrapolated from this graph. The method can be performed at four different temperatures (25°C, 50°C, 75°C, 80°C).

During use, impurities, acids or mixing can change the air release time. Too much air in the oil damages the structure of a stable lubricating film in slide bearings in turbines, for example. Air bubbles dispersed in the oil can impede the function of hydraulic systems and cause cavitation.

A high proportion of air bubbles in the oil can cause a "diesel effect" to occur. The air release time in comparison to fresh oil allows conclusions to be drawn regarding further use of lubricating or hydraulic oil in breakdowns or critical operating conditions.