RMF Systems CMS 2 - NAS1638 Cleanliness Code System (Now Defunct, Replaced by SAE AS4059 E Table 1); SAE AS4059 REV E Cleanliness Classification for Hydraulic Fluids

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As a policy of continual improvement, RMF reserves the right to alter the specification without prior notice.
201.028 REV 1 Date of Issue: 18 June 2018
Microscope counting examines the particles differently to APCs and the code is given with two scale numbers
only. These are at 5μm and 15μm equivalent to the 6μm(c) and 14μm(c) of the APCs (Figure 11.2)
11.5 NAS1638 Cleanliness Code System (now defunct, replaced by SAE AS4059E Table
1)
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 4406:1999. 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 CMS
software.
00
0
1
2
3
4
5
6
7
8
9
10
11
12
5-15
125
250
500
1000
2000
4000
8000
16000
32000
64000
128000
256000
512000
1024000
15-25
22
44
89
178
356
712
1425
2850
5700
11400
22800
45600
91200
182400
25-50
4
8
16
32
63
126
253
506
1012
2025
4050
8100
16200
32400
50-100
1
2
3
6
11
22
45
90
180
360
720
1440
2880
5760
Over 100
0
0
1
1
2
4
8
16
32
64
128
256
512
1024
Table 11.1 Contamination Level Classes according to NAS1638 (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.
11.6 SAE AS4059 REV E Cleanliness Classification for Hydraulic fluids
This SAE Aerospace Standard (AS) defines cleanliness levels for particulate contamination of hydraulic fluids and
includes methods of reporting data relating to the contamination levels. Tables 11.2 and 11.3 below provide the
Maximum Contamination Limits (Particles/100ml) of differential and cumulative particle counts respectively for
counts obtained by an automatic particle counter, e.g. CMS.
Size Range
μm(c):
6-14
14-21
21-38
38-70
>70
Class
00
125
22
4
1
0
0
250
44
8
2
0
1
500
89
16
3
1
2
1000
178
32
6
1
3
2000
356
63
11
2
4
4000
712
126
22
4
5
8000
1425
253
45
8
6
16000
2850
506
90
16
7
32000
5700
1012
180
32
8
64000
11400
2025
360
64
9
128000
22800
4050
720
128
10
256000
45600
8100
1440
256
11
512000
91200
16200
2880
512
12
1024000
182400
32400
5760
1024
Table 11.2 AS4059E Table 1 Cleanliness Classes for Differential Particle Counts