Example of differing oil cleanliness
standards:
|
Sample 1 |
Sample 2 |
ISO 4406 |
15/12 |
15/12 |
NAS 1638 |
6 |
6 |
- Gravimetric test ASTM F
- 313-78 0.8µ membrane
|
 |
 |
- Contaminant level
- mg/100ml
|
6 |
<1 |
By looking
at the ISO and NAS grades for each sample you would believe that
both are clean. If this is the case, then why does a servo valve
fail in one of the systems.
The answer is not in the ISO
or NAS grade, but in the gravimetric test, which shows sample
1 to be heavily contaminated with high levels of oxidation, also
evident by the build up of deposits on the valve itself.
Oil in sample 2 is very clean
and has been acheived by the use of an ELC unit.
|