74
As a policy of continual improvement, STAUFF reserves the right to alter the specification without prior notice.
201.031
Date of Issue: 06 November 2018
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 LPM software.
00
0
1
2
3
4
5
6
7
8
9
10
11
12
5-15
125
250
500
100
0
200
0
400
0
800
0
16000
32000
64000
12800
0
25600
0
51200
0
1024000
15-25
22
44
89
178
356
712
142
5
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. LPM.
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