The NAS 1638 cleanliness standard was developed for aerospace components in the US and is still widely used for industrial and aerospace fluid power applications. The figures are differential counts, and the NAS class is usually reported as a single figure representing the maximum allowed particle counts (i.e. worst case) for designated particle

NAS 1638 saw widespread acceptance in the 1970s and 1980s by industries where reliability was a prerequisite, in areas such as offshore oil production, iron and steel industries, etc. It led to the development of other coding systems, the most notable being the International Organization for Standardization (ISO) 4406 2 .

Standard NAS 1638 has been developed in order to define the levels of contamination in the aerospace sector. Standard NAS 1638 has been replaced by standard AS4059, the E version of which has been adapted so as to provide data on the levels of contamination for both cumulative and differential values.

The two most likely to be encountered in the oil & gas, and process industries are The ISO Cleanliness Code (ISO 4406), and The NAS 1638 cleanliness standard. An introduction to each of these allowable particle contamination standards is provided below.

In NAS 1638 classification the code number refers to a maximum quantity of particles within a specific size class. Most users use a single code number based on the highest particle count in any of the size ranges.

2023年1月26日 · Oil cleanliness is generally defined by two different particle count rating systems: the National Aerospace Standard (NAS) 1638 and the International Standards Organization (ISO) 4406. These both provide a classification of the number of particles to rate cleanliness

Both NAS 1638 and ISO 4406 focus on the methods for calculating particle counts or solid contamination levels within a fluid. NAS 1638 represents the counts of particles in five size groups: 5 to 15 microns per 100 milliliters (mL)

Purity classes according to ISO 4406 / NAS 1638 About 80% of hydraulic system failures are caused by contamination of the hydraulic oil. Therefore, in addition to the basic properties such as viscosity and wear protection, the purity of the hydraulic oil is particularly crucial for trouble-free and low-wear operation of the machines.

The NAS 1638 [1] is a legacy system for aerospace and industrial fluid power applications. This system was conceived in the 1960s to help the U.S. Aerospace industry measure and control particle contamination delivered in aircraft hydraulic components. It assigns a cleanliness class based on either a particle count or weight.

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.