A Closer Look at ISO Codes
As industry maintenance practices continue to evolve and maintenance professionals realize the substantial cost saving benefits of contamination control efforts and fluid cleanliness, we find ISO codes entering our daily conversations more often. Cleaner fluids translate to reduced wear and longer component life. ISO codes are simply a ‘shorthand’ method of quantifying fluid cleanliness.
Language of Cleanliness
Fluid analysis laboratories measure fluid cleanliness with specialized equipment that categorizes particles in the fluid by size and counts the number of particles per volume of the sample in each category or size range. The sample report shows the absolute number of particles equal to or larger than each of the following sizes: 4, 6, 10, 14, 21, 38, 70, and 100 microns.
That’s a total of 8 different numbers to describe fluid cleanliness, which makes it cumbersome to compare and discuss results.
Translating Codes: What Do They Mean?
The ISO 4406 standard simplifies that data by only looking at three size ranges (4, 6, and 14 microns). It further simplifies the data by assigning codes to correspond to a range of particle counts. For example, rather than saying there are 1,890 particles 4 microns or larger, the standard assigns a ‘code’ of 18 (which includes particles counts from 1300 to 2500). A similar code is assigned for the 6 and 14 micron size range. So now the fluid cleanliness is reduced to three numbers (or codes). For example, 18/15/13. That is a much easier way to include fluid cleanliness in our comparisons and discussions.
But, this also means that without a thorough understanding of what those codes mean, we can easily jump to poor conclusions. In a simple example, a change in ISO code from 18/15/13 to 19/15/13 might lead to the assumption that the number of particles between 4 and 6 microns has doubled (since each increase in ISO code doubles the upper and lower range of the previous code). Consider if the actual particle counts at 4 microns were 2485 initially and increased to 2510; the code assigned does indeed increase from 18 to 19, but the absolute particle count is nowhere close to doubling. Conversely, if the initial count was 1310 and the next sample increased to 2490, the number of particles has indeed nearly doubled, but the ISO code has remained at 18.
Understanding ISO Code Shorthand
ISO codes are a great way to simplify our comparisons and discussions on the important topic of fluid cleanliness. But having a thorough understanding of what that ‘shorthand’ notation means, can also save us from overlooking the more subtle picture of what is happening to our fluids.
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