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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
ISO 4402:1991
Hydraulic fluid power
Calibration of liquid automatic particle counters.
ISO 4406:1987
Hydraulic fluid power
Code for defining the level of contamination by solid particles
ISO 4572:1981
Hydraulic fluid power
– Filters
Multi-pass method for evaluating filtration performance of a filter element
In order that users are not confused by the changes to these standards, particularly by reference to them
in technical literature, ISO is updating 4402 to ISO 11171, and 4572 to ISO 16889.
Two standards which concern our industry are the ISO 4406 coding system and the new ISO 16889
Multi-pass test. As APCs will henceforth count particles more accurately, there will now be a change in
the way sizes are labelled.
In the new ISO 4406:1999, new calibration sizes are used to give the same cleanliness codes as the
‘old’ calibration sizes of 5 and 15μm. In this way, there will be no necessity to change any system
cleanliness specifications. It is proposed that the cleanliness codes (for APCs) will be formed from three
particle counts at 4, 6 and 14μm, with 6 and 14μm corresponding very closely to the previous 5 and
15μm measurements.
This will ensure consistency in data reporting.
As the counts derived by microscope counting methods are not affected, the particle sizes used for
microscopy will remain unchanged (i.e. at 5 and 15μm).
To clarify matters still further, ISO standards written around the new test dust will utilize a new identifier,
“(c)”. Hence μm sizes according to the new ISO 11171 will be expresses as “μm(c)” and Beta ratios
according to ISO 16889 will be expressed as
“Bx(c)”, e.g.”B5(c)”.
However, it must be stressed that the only real effect users will experience will be the improved accuracy
in particle counts - there will be no change in the performance of filters, nor in the ISO cleanliness levels
that they will achieve.
The following charts show the correlation between the old ACFTD and the new ISO MTD.
The LPM is calibrated with ISO Medium Test Dust (to ISO 11171). The correlation between particle sizes
and the ACFTD (old standard) to the ISO MTD (new standard) is as follows:
ACFTD
<1
5
15
25
30
50
75
100
ISO MTD
4
6
14
21
25
38
50
70
Correlation
The table shows the correlation between Particle Sizes Obtained using ACFTD (ISO 4402:1991) and
NIST (ISO 11171) Calibration Methods
This table is only a guideline.
The exact relationship between ACFTD sizes and the NIST sizes may vary from instrument to instrument
depending on the characteristics of the particle counter and original ACFTD calibration.
Particle Size Obtained Using