Is air the new dirt for your oil?

img 4770 1024x565 Is air the new dirt for your oil?

We often talk about dirty oil or wet oil. We measure these contaminants routinely on your oil analysis and nobody questions it as necessary. However, did you know there is a 3rd contaminant that labs hardly ever measure. It’s just as ubiquitous as dirt and water and you can find it everywhere. In fact I know you are surrounded by it right at this moment whilst reading this. That substance is air.

Air as far as your lubricant is concerned is a contaminant just like dirt or water. It can cause wear and often more severe problems than dirt and water. So I thought it was about time I wrote an article on the subject of air contamination in your oil.

Why is air a problem?

Air is ultimately a huge problem for your machinery. Approximately 3% to 10% of your oil volume is dissolved or suspended air bubbles. If this rises this can have a number of severe consequences. Namely:

Pump showing serious surface cavitation received at oil analysis laboratories as part of a failure investigation.
The process of cavitation.

In summary is air in my oil an issue?

So overall it is literally better out than in when it comes to air in your oil. Now that doesn’t mean a new process of burping oil barrels, but does mean there are some new tests you should be aware of to first of all see if you have a gas problem with your lubricant.

Better out than in. A gas filled oil can give you a whole load of problems.

So how do I know I have got really bad gas problem (in my lube oil)?

There are two tests the lab can perform to assess this – foaming tendency and air release. I already have covered articles on foaming before including traditional foaming and our exclusive H-FOAM test add on to your foaming tendency analysis here.

Air release

Air release works by measuring the time an extremely aerated oil takes to release that gas. Since air is less dense than oil, the density of an aerated oil is less than a non-aerated one. Hence the process involves measuring the time for the density of the oil to return to within 0.2% of the original value. The longer it takes the poorer the oil is at releasing air from it.

How does air release work?

180ml of oil is added to a special piece of glassware that has a water warming jacket and an air inlet and outlet ports.

The density of this oil is measured at the agreed temperature for the test as a starting point.

The oil can be at several temperatures between 25’c and 75’C as agreed with the client, but it is common to use 50’C as the temperature for the test.

The air flow into the sample is actually quite ferocious to really help entrain gas in the oil.

At the end of 10 minutes of air being pumped through the density will be a lot less than the start. As the air releases the density will increase back to normal. This is measured continuously until it returns to within 0.2% of the original sample density at the test temperature.

What’s a normal air release time?

Typically you want the oil to have returned to normal within 10 minutes, but some manufacturers have even tighter limits as much as 5 minutes. A typical turbine oil will have a new oil air release between 3 and 6 minutes.

Why might an air release rise over time?

Usually contamination or oil degradation are the most common causes, but it can also be wrong lubricant choice too.

How do I find out more?

You can find out more by clicking the contact us button in blue on the bottom right of this screen.

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