![iso 4406 table iso 4406 table](https://gpmhydraulic.com/wp-content/uploads/2015/04/ISO-4406-Level.jpg)
Therefore, only an approximate assignment between NAS and ISO is possible for unknown particle numbers (see table below). OELCHECK can determine the purity class according to both ISO 4406 and SAE 4059 and determines the purity classes for mineral and biodegradable hydraulic oils, among others, starting with analysis kit 2. Note: ISO 4406:99 states particles per 1mL. The table on the left shows the number of particles in 100mL.
![iso 4406 table iso 4406 table](https://fluidpowerjournal.com/wp-content/uploads/2015/11/helgerson-iso-table1-1007x1024.png)
"NAS 9".Īn exact assignment between NAS class and ISO purity class and vice versa is not possible due to the different counting methods: The highest of the 5 determined NAS numbers results in the NAS class, e.g. Each number refers to an ISO Range Code, which is determined by the number of particles for that size (4, 6 and 14 micron) and larger present in 1 ml of fluid. These numbers correspond to 4, 6 and 14 micron, in that order. With the NAS 1638, an NAS number (0 to 12) is determined for each of the 5 counting ranges. Cleanliness levels are defined by three numbers divided by slashes (/). In the case of an indicationwith 2 numbers, such as "15/12", the smallest ISO size class is not taken into account because, for example, the particles were counted optically using a microscope. The indication of the purity class according to ISO is carried out in 3 classes, for example with "20/15/12", where each number stands for one of the 3 counting classes.