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Contaminants |
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Contaminants can be divided into three groups
A) Hard Contaminants: Dust, Fibrous matter & Wear metal.
B) Soft Contaminants: These are the by products of oil Oxidation.
C) Water: Free or emulsified.
Are there really so many particles below 5 microns?
Yes, it is a fact that smaller particles are larger in number than larger particles. It is as natural as saying that the number of rats is more than the number of elephants in a jungle and ants are profoundly more numerous than rats!! |
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There is a standard test dust which is used to measure the capacity of filters. This test dust (single cut dust) shows the above distribution of particles. It is clear that smaller particles increase exponentially in nos. and 85% of the particles are between 2-5 microns in size, when measured on a 2-80 micron scale. The graph is very intriguing, it shows particle sizes in a sample of oil having only 1mg / Litre of contaminants by weight. Even in such a small level of contamination, particles below 5 microns are in millions, and bigger ones in thousands.
This is true of all particle analyses that you may see. The sample of new oils tested in the table shows the same pattern. |
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| Particle size in Microns |
5-14 |
15-24 |
25-49 |
50-100 |
>100 |
| New Oil 1 |
135000 |
46000 |
18600 |
5400 |
4700 |
| New Oil 2 |
520000 |
150000 |
50000 |
14000 |
12000 |
| Typical aircraft co.
System Limit |
10000 |
3500 |
7500 |
30 |
5 |
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Figures taken from Moog Bulletin 701 by Moog Servocontrols NY.
It is also a fact that smaller particles only can enter clearances and cause damage to mating parts!
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