Standard NAS 1638 has been replaced by standard AS4059, the E version of which has been adapted so as to provide data on the levels of contamination for both cumulative and differential values. Standard NAS 1638 has been developed in order to define the levels of contamination in the aerospace sector. In this case, that however does not represent a sufficiently exhaustive picture of the status of the oil, the maximum value of the various sizes is taken into consideration. The NAS class is identified with a single value. A class identification is attributed to each of these ranges of values, based on a numerical comparison of the particles present with a standardised table. In standards NAS 1638 and AS4059E, the particles are grouped into intervals as per size: between 5 and 15 µm, between 15 and 25 µm, between 25 and 50 µm, between 50 and 100 µm and, finally, over 100 µm. The sizes of the particles of interest will be those appropriate to the power of removal of the filter. In a hydraulic system, the fluid re-circulates and tends to reach a stable level of contamination over time, that reflects the characteristics of the type of filter used. Standard NAS 1638 is still used, yet due to the fact that by now it is considered obsolete, it has been replaced by standard AS4059 / ISO 4406 that concerns the encoding of the level of contamination of a fluid. Test benches for the oil hydraulics sectorĮncoding method of the level of contamination based on the number of particles per unit of volume divided into size classes.
Automotive cooling/thermoregulation systems.Cleaning and oil purification operations.
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