Danfoss Vickers Target-Pro 2 Operation Manual page 13

NAS [National Aerospace Standard] 1638 Cleanliness Code System
The NAS system was developed in 1964 to define classes
of contamination in aircraft components.This standard was
extended to industrial hydraulic systems simply because
nothing else existed at the time.
The coding system defines the maximum numbers permit-
ted of 100ml volume at various size intervals (differential
counts) rather than using cumulative counts as in ISO 4406.
Maximum Contamination Limits (per 100 ml)
Size Range Classes (in microns)
00 0 1
5–15 125 250 500
15–25 22 44 89
25–50 4 8 16
50–100 1 2 3
Over 100 0 0 1
Cleanliness Code Chart (with 100mL sample volume)
H y d r a u l i c C o m p o n e n t M a n u f a c t u r e r s '
R e c o m m e n d a t i o n s
Manufacturers know the effects of contamination. They issue
maximum permissible contamination levels, and
remind users that cleaner fluids will improve performance
and increase component life. But no one has established a
single standard for the cleanliness of hydraulic fluid, in part
because working conditions are different for any two appli-
cations. As a result, even trusted sources of information on
cleanliness levels give varying recommendations.
The table below should help you get started. It gives a
selection of maximum contamination levels that aretypical-
ly issued by component manufacturers. These relate to the
use of the correct viscosity mineral fluid. An even cleaner
level may be needed if the operation is severe, such as high
frequency fluctuations in loading, high temperature or high
failure risk.
Note: The recommendations in this table should be viewed as
starting levels; adjust them as needed to reflect opera-
tional experiences or user requirements.
Ta r g e t C l e a n l i n e s s L e v e l s
You can use cleanliness levels to establish bench-
marks. If you have no component failures over a
prolonged testing period, the average level meas-
ured during that time may be an acceptable goal. If
you need to reduce equipment failures, want to
increase component life, or expect conditions to
change considerably, you can establish a higher
benchmark and use testing to help reach it.
An acceptable level of cleanliness depends on
three features: 1. the contamination sensitivity of
components; 2. the operational conditions of the
system; 3. and the required reliability and life
expectancy.
2 3 4 5
1000 2000 4000 8000
178 356 712 1425
32 63 126 253
6 11 22 45
1 2 4 8
Contamination
Codes
ISO4406
4µm(c) 6µm(c) 14µm(c)
14
17
18
20
21
23
Vickers by Danfoss Target-Pro 2 Analyzer and Sampler Operation Manual V-PP-MC-0002-E
Although the standard provides no guidance for quoting lev-
els, most industrial users quote the highest code recorded
in all sizes; this convention is used on the Target-Pro 2.
Contamination Level Classes according to NAS 1638
(January 1964)
Each contamination class is defined by a number from 00 to
12 that indicates the maximum particles per 100 ml, counted
on a differential basis, in a given size bracket.
6 7 8
16000 32000 64000
2850 5700 11400
506 1012 2025
90 180 360
16 32 64
U N I T T Y P E
Pump Piston (slow speed, in-line)
Piston (high speed, variable)
Gear
Vane
Motor Axial piston
Radial piston
Gear
Vane
Valve Directional (solenoid)
Pressure control (modulating)
Flow control
Check valve
Cartridge valve
Proportional
Servo valve
Actuator
Typical Manufacturer Recommendations for Component Cleanliness (ISO 4406)
Correspondent Recommended Typical
Codes
NAS1638
12 9 3
15 11 6
16 13 7
18 14 9
19 16 10
21 18 12
9 10 11
128000 256000 512000 1024000
22800 45600 91200
4050 8100 16200
720 1440 2880
128 256 512
I S O 4 4 0 6 C O D E
2 2 / 2 0 / 1 6
1 7 / 1 5 / 1 3
1 9 / 1 7 / 1 5
18/16/14
18/16/13
19/17/13
20/18/15
19/17/14
20/18/15
19/17/14
19/17/14
20/18/15
20/18/15
18/16/13
16/14/11
20/18/15
Filtration Applications
Degree
Bx ≥ 200
3 High precision and
laboratory servo-systems
3–6 Robotic and
servo-systems
10–12 Very sensitive–high
reliability systems
12–15 Sensitive–reliable systems
15–25 General equipment
of limited reliability
25–40 Low-pressure equipment
not in continuous service
July 2023
12
182400
32400
5760
1024
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