ISO, The International Organization for Standardization has developed a code called the ISO 4406 Cleanliness Standard. This standard applies to the cleanliness of hydraulic fluids and lubrication systems. It has become the primary piece of data used in most industrial oil analysis reports. Most manufacturers, or end users develop their own target criteria for their fluids and use lab reports to monitor, achieve and maintain these standards.

ISO 4406 quantifies particulate contamination levels per milliliter of fluid in three sizes: >4-micron, > 6-micron and > 14-micron. An example of an analysis rated at the level of the ISO Cleanliness Standard is 19/17/14. Each of these three numerals represents a contaminant level code for the associating particle size. The code will include any particles present that meet the predetermined size or larger. It is important you note that each increase in the code represents an increase in the quantity of particles within that predetermined size range by 100%. Therefore, each decrease by one reduces the presence by one half.

How the ISO Cleanliness Code is Determined

Many fluid samples provided to laboratories for testing are receiving particle counting by what is known in the industry as automatic particle counting or APC. The current calibration standard for APC is ISO 11171. Particles subjected to APC are generally counted utilizing either a laser or a pore blockage method. The reports from different laboratories tend to vary greatly in terms of micron levels. These counts are not standardized and tend to vary greatly, oftentimes by the criteria set forth by the end user. An example of reported micron levels reported is 4, 6, 10, 14, 21, 38, 70, and 100 microns.


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