When we think about measuring air in oil, the top-of-mind lab tests that are well known are the foam test (ASTM D892) and the Air Release test (ASTM D3427 & DIN ISO 9120). While these two tests can provide information on the tendency of foam to dissipate or for air to be released from the oil, they don’t give the entire story of what’s happening in the oil as it relates to air.
More specifically, they do not take into account the volume of air that can be trapped in your system during operation, nor how long it will take to dissipate when everything stands still. These parameters are critical for determining the impact of entrapped air in your oil.
People can also measure the volume of air in the oil, but 5% can mean different things depending on the air’s state, as shown in Figure 2 below.
As we can see in Figure 2, an air (gas) volume fraction of 5% may appear the same, but it can affect your system differently.
In Scenario A, the bubble sizes are larger, so these will rise to the surface more quickly and dissipate. As such, there are fewer disturbances and pressure fluctuations.
In this case, these might indicate localized entrainment, suggesting churning or impact from your return line. Another source could be coalescence, driven by oil properties, splash effects, and other factors. The risk of air bubbles becoming trapped in dead zones increases.
However, in Scenario B, the average bubble size is smaller, which means there are many more air bubbles in the oil! This means that there is a higher surface contact area and an increased potential for foaming. This can increase the rate of oxidation and, by extension, the risk of the oil forming varnish.
This also significantly affects the oil’s compressibility. With the advent of these smaller bubbles, there is usually system-wide aeration, such as vortexing or suction issues. The risk of inefficient cooling and overheating your oil in heaters has increased significantly.
With only a 5% air volume result, we would be missing critical information, such as what could be causing the issue or whether it is an immediate threat to our operations. This is where the SBS (Smart Bubble System) changes the entire game.
Find out more in the full article, "Air in Oil: The Reliability Variable Many Programs still treat too late" featured in Reliable by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd, David Placzek, Dr. Lukas Hafner
