NAS Cleanliness codes

NAS 1638 Code ...

The NAS system was originally developed in 1964 to define contamination classes for the contamination contained within aircraft components. The application of this standard was extended to industrial hydraulic systems simply because nothing else existed at the time

The coding system defines the maximum numbers permitted of 100mL volume at various size intervals (differential counts) rather than using cumulative counts as in ISO 4406.

Although there is no guidance given in the standard on how to quote the levels, most industrial users quote a single code which is the highest recorded in all sizes and this convention is used on the LPA2.

CONTAMINATION LEVEL CLASSES according to NAS 1638 (January 1964)

The contamination classes are defined by a number (from 00 to 12) which indicates the maximum number of particles per 100 ml, counted on a differential basis, in a given size bracket.

MAXIMUM CONTAMINATION LIMITS (PER 100 mL)

                                                           size range in microns