What is in this article?:
Today's emphasis on pollution prevention and waste stream minimization has made the benefits of contamination control programs for hydraulic fluids even more compelling.
Reporting fluid cleanliness
The changes discussed in the previous sections will not affect the actual cleanliness of fluids in the field. However, for those technicians reporting data using particle counts, the changes in APC calibration will affect results obtained from both laboratory and portable equipment that is calibrated to the new standards, as in Table 3.
Table 3: Typical effect of new calibration on particle counts
|APC with old (ACFTD) calibration||APC with new (NIST) calibration|
|Particle size in µm||Particles/mL||Particle size in µm(c)||Particles/mL|
Technicians reporting data using the ISO cleanliness codes will notice less effect. The adoption of a cleanliness code with 3 digits should not have any appreciable impact because 3-digit codes have been used by industry for a number of years. In addition, the change from 5- and 15-µm sizes to 6- and 14-µm(c) sizes will not show a significant change in fluid-cleanliness code. The primary change will come from adoption of the 4-µm(c) size. This is a new addition to the ISO 4406 standard (although a third digit at 2 µm using ACFTD had been used). Because the new 4-µm(c) size equates to about 1 µm using ACFTD calibration, particle counts on fluid samples will typically show an increase of about one level for this first digit of the code, Table 4. The reason: there usually are more smaller particles in any fluid sample.
Table 4: ISO code exampleOld 2-digit ISO code
(5 µm/15 µm)
Old 3-digit ISO code
(2 µm/5 µm/15 µm)
New 3-digit ISO code
(4 µm(c)/6 µm(c)/14 µm(c))
ISO MTD was chosen as a replacement for Air Cleaner Fine Test Dust because ACFTD is no longer being manufactured. To gain better resolution, accuracy, repeatability, and reproducibility in tests using the replacement dust, four new or revised ISO standards have been adopted to accommodate the new test dust. These changes will have an impact on automatic particle-counter calibration, particle-size definition, and laboratory reporting of filter performance - both in particle-removal efficiency (fine filters will appear coarser and coarse filters finer) and dirt-holding capacity (capacity will likely increase). The changes also will effect laboratory reporting on system fluid cleanliness (typically showing a higher contamination level at smaller particle sizes).
This will undoubtedly cause some confusion, but remember that any impact is merely an artifact of the minor changes in testing. Actual filter performance and field fluid contamination levels will remain the same.