ISO 23369:2022
(Main)Hydraulic fluid power — Multi-pass method of evaluating filtration performance of a filter element under cyclic flow conditions
Hydraulic fluid power — Multi-pass method of evaluating filtration performance of a filter element under cyclic flow conditions
This document specifies: a) A multi-pass filtration performance test under cyclic flow conditions with continuous contaminant injection for hydraulic fluid power filter elements. b) A procedure for determining the contaminant capacity, particulate removal and differential pressure characteristics. c) A test currently applicable to hydraulic fluid power filter elements that exhibit an average filtration ratio greater than or equal to 75 for particle sizes ≤25 µm(c), and a final test system reservoir gravimetric level of less than 200 mg/L. It is necessary to determine by validation the range of flow rates and the lower particle size limit that can be used in test facilities. d) A test using ISO 12103‑1 A3 medium test dust contaminant and a test fluid. This document provides a test procedure that yields reproducible test data for appraising the filtration performance of a hydraulic fluid power filter element without influence of electrostatic charge. This document is applicable to three test conditions: — Base upstream gravimetric level of 3 mg/L; — Base upstream gravimetric level of 10 mg/L; — Base upstream gravimetric level of 15 mg/L.
Transmissions hydrauliques — Évaluation des performances d’un élément filtrant par la méthode de filtration multi-passe sous débit cyclique
Le présent document spécifie: a) un essai d’évaluation des performances de filtration d’éléments filtrants de transmissions hydrauliques, multi-passe sous débit cyclique, avec injection continue de polluants; b) un mode opératoire permettant de déterminer leur capacité de rétention des polluants, ainsi que leurs caractéristiques en matière d’élimination des particules et de pression différentielle; c) un essai applicable à l’heure actuelle aux éléments filtrants de transmissions hydrauliques ayant un rapport de filtration moyen égal ou supérieur à 75 pour les tailles de particules inférieures ou égales à 25 µm(c) et une concentration finale dans le réservoir du circuit d’essai inférieure à 200 mg/l. Il est nécessaire de déterminer par validation la plage des débits et la limite inférieure de taille de particules pouvant être utilisées avec les installations d’essai; d) un essai utilisant le contaminant ISO12103-1 A3 «Medium Test Dust» («poussière d’essai moyenne») comme polluant, ainsi qu’un fluide d’essai. Le présent document fournit un mode opératoire d’essai générant des données d’essai reproductibles pour l’évaluation des performances de filtration d’un élément filtrant de transmission hydraulique non soumis à l’influence de charges électrostatiques. Le présent document est applicable à trois conditions d’essai: 1) essai réalisé avec une concentration amont de base de 3 mg/l; 2) essai réalisé avec une concentration amont de base de 15 mg/l; 3) essai réalisé avec une concentration amont de base de 15 mg/l.
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INTERNATIONAL ISO
STANDARD 23369
Second edition
2022-12
Hydraulic fluid power — Multi-
pass method of evaluating filtration
performance of a filter element under
cyclic flow conditions
Transmissions hydrauliques — Évaluation des performances d’un
élément filtrant par la méthode de filtration multi-passe sous débit
cyclique
Reference number
ISO 23369:2022(E)
© ISO 2022
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ISO 23369:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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ISO 23369:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 4
5 General procedure .5
6 Test equipment .5
7 Measurement accuracy and test condition variation . 7
8 Filter performance test circuit validation procedures . 8
8.1 General . 8
8.2 Filter test system validation . 8
8.3 Contaminant injection system validation . 9
9 Summary of information required prior to testing a filter element .9
10 Preliminary test preparation .10
10.1 Test filter assembly . 10
10.2 Contaminant injection system . . 10
10.3 Filter test system . 11
11 Filter performance test .12
12 Calculations .14
13 Data presentation .17
14 Identification statement (reference to this document) .18
Annex A (normative) Base test fluid properties .19
Annex B (informative) Test system design guide .21
Annex C (informative) Example report, calculations and graphs .26
Bibliography .35
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ISO 23369:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
This second edition cancels and replaces the first edition (ISO 23369:2021), which has been technically
revised.
The main changes are as follows:
— calculation of ramp time.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 23369:2022(E)
Introduction
In hydraulic fluid power systems, one of the functions of the hydraulic fluid is to separate and lubricate
the moving parts of components. The presence of solid particulate contamination produces wear,
resulting in loss of efficiency, reduced component life and subsequent unreliability.
A hydraulic filter is provided to control the number of particles circulating within the system to a level
that is commensurate with the degree of sensitivity of the components to contaminants and the level of
reliability required by the users.
Test procedures enable the comparison of the relative performance of filters so that the most
appropriate filter can be selected. The performance characteristics of a filter are a function of the
element (its medium and geometry) and the housing (its general configuration and seal design).
In practice, a filter is subjected to a continuous flow of contaminant entrained in the hydraulic fluid until
some specified terminal differential pressure (relief-valve cracking pressure of differential-pressure
indicator setting) is reached.
Both the length of operating time (prior to reaching terminal pressure) and the contaminant level at
any point in the system are functions of the rate of contaminant addition (ingression plus generation
rates) and the performance characteristics of the filter.
Therefore, a realistic laboratory test establishes the relative performance of a filter by providing the
test filter with a continuous supply of ingressed contaminant and allowing the periodic monitoring of
the filtration performance characteristics of the filter. A standard multi-pass method for evaluating
the performance of hydraulic fluid power filter elements under steady-state flow conditions has
been developed as ISO 16889. That test procedure provides a basis for the comparison of the relative
performance characteristics of various filter elements. The results from such a test, however, might not
be directly applicable to most actual operating conditions.
In actual operation, a hydraulic fluid power filter is generally not subjected to steady-state flow but
to varying degrees of cyclic flow. Tests have shown that, in many instances, the filtration capabilities
of an element are severely reduced when subjected to varying cyclic flow conditions. It is therefore
important to evaluate the filtration performance of a filter for applications under cyclic flow conditions.
The cyclic flow multi-pass test procedure for hydraulic filters specified in this document has been
developed to supplement the basic steady-state flow test (ISO 16889) for filter elements that are
expected to be placed in service with cyclic flow. The recommended flow cycle rate of 0,1 Hz is a result
of an industry survey and a broad range of test results. If much higher cycle rates are expected in
actual service, the test should be conducted at that frequency to produce more meaningful results. The
procedure specified in this document may be applied at a cycle rate other than 0,1 Hz, if agreed upon
between the supplier and user. However, only values resulting from testing at the 0,1 Hz cycle rate may
be reported as having been determined in accordance with this document.
Fluid samples are extracted from the test system to evaluate the filter element’s particulate removal
characteristics. To prevent this sampling from adversely affecting the test results, a lower limit is
placed upon the rated flow rate of filter elements that should be tested with this procedure.
The current maximum flow rate specified in this document is based upon the maximum gravimetric
level of injection systems that have been qualified to date.
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INTERNATIONAL STANDARD ISO 23369:2022(E)
Hydraulic fluid power — Multi-pass method of evaluating
filtration performance of a filter element under cyclic flow
conditions
1 Scope
This document specifies:
a) A multi-pass filtration performance test under cyclic flow conditions with continuous contaminant
injection for hydraulic fluid power filter elements.
b) A procedure for determining the contaminant capacity, particulate removal and differential
pressure characteristics.
c) A test currently applicable to hydraulic fluid power filter elements that exhibit an average filtration
ratio greater than or equal to 75 for particle sizes ≤25 µm(c), and a final test system reservoir
gravimetric level of less than 200 mg/L. It is necessary to determine by validation the range of flow
rates and the lower particle size limit that can be used in test facilities.
d) A test using ISO 12103-1 A3 medium test dust contaminant and a test fluid.
This document provides a test procedure that yields reproducible test data for appraising the filtration
performance of a hydraulic fluid power filter element without influence of electrostatic charge.
This document is applicable to three test conditions:
— Base upstream gravimetric level of 3 mg/L;
— Base upstream gravimetric level of 10 mg/L;
— Base upstream gravimetric level of 15 mg/L.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2160, Petroleum products — Corrosiveness to copper — Copper strip test
ISO 2942, Hydraulic fluid power — Filter elements — Verification of fabrication integrity and determination
of the first bubble point
ISO 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods
ISO 3968, Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow
ISO 4021, Hydraulic fluid power — Particulate contamination analysis — Extraction of fluid samples from
lines of an operating system
ISO 4405, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the gravimetric method
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
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ISO 23369:2022(E)
ISO 11943:2021, Hydraulic fluid power — Online automatic particle-counting systems for liquids —
Methods of calibration and validation
ISO 12103-1, Road vehicles — Test contaminants for filter evaluation — Part 1: Arizona test dust
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
contaminant mass injected
m
i
mass of specific particulate contaminant injected into the test circuit to obtain the terminal differential
pressure
3.2
differential pressure
difference between the tested component inlet and outlet pressures as measured under the specified
conditions
Note 1 to entry: See Figure 1 for a graphical depiction of differential pressure terms.
3.3
clean assembly differential pressure
difference between the tested component inlet and outlet pressures as measured with a clean filter
housing containing a clean filter element
3.4
clean element differential pressure
differential pressure of the clean element calculated as the difference between the clean assembly
differential pressure (3.3) and the housing differential pressure (3.6)
3.5
final assembly differential pressure
assembly differential pressure at the end of a test, equal to the sum of the housing differential pressure
and the terminal element differential pressure
3.6
housing differential pressure
differential pressure of the filter housing without an element
3.7
terminal element differential pressure
maximum differential pressure across the filter element as designated by the manufacturer to limit
useful performance
3.8
rest conductivity
electrical conductivity at the initial instant of current measurement after a DC voltage is impressed
between electrodes
Note 1 to entry: Rest conductivity is the reciprocal of the resistance of uncharged fluid in the absence of ionic
depletion or polarization.
2
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ISO 23369:2022(E)
3.9
retained capacity
m
R
mass of specific particulate contaminant effectively retained by the filter element when terminal
element differential pressure is reached
3.10
cyclic flow
change of flow from the specified rated flow rate to 25 % of rated flow rate at a specified frequency and
waveform
Key
1
differential pressure ΔP )
()
2 test time or contaminant mass injected
3 final assembly differential pressure (end of test)
4 terminal element differential pressure
5
clean element differential pressure at q
max
6
housing differential pressure at q
max
7
clean assembly differential pressure at q
max
Figure 1 — Differential pressure conventions for multi-pass test under cyclic flow conditions
3
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ISO 23369:2022(E)
4 Symbols
Table 1 — Symbols
Symbol Unit Description
overall average upstream count of particles larger than size x
particles per millilitre
A
u,x
overall average downstream count of particles larger than size x
particles per millilitre
A
d,x
filtration ratio at particle size x (ISO 11171 calibration)
a
α –
x()c
filtration ratio at particle size x and time interval t
–
α
xt,
α –
average filtration ratio at particle size x (ISO 11171 calibration)
x()c
a
litres per second
rise and fall ramp flow rate acceleration
squared
milligrams per litre average base upstream gravimetric level
c
b
'
milligrams per litre desired base upstream gravimetric level
c
b
milligrams per litre average injection gravimetric level
c
i
'
milligrams per litre desired injection gravimetric level
c
i
milligrams per litre test reservoir gravimetric level at 80 % assembly differential pressure
c
80
m
grams mass of contaminant needed for injection
grams estimated filter element contaminant capacity (mass injected)
m
e
m grams contaminant mass injected
i
grams contaminant mass injected at element differential pressure
m
P
m grams retained capacity
R
N – number of counts in specific time period
particles per millilitre number of upstream particles larger than size x at count i
N
u,xi,
number of downstream particles larger than size x at count i
N particles per millilitre
d,xi,
average upstream count of particles larger than size x at time interval
particles per millilitre
N
u,xt,
t
average downstream count of particles larger than size x at time
particles per millilitre
N
d,xt,
interval t
p
Pa or kPa (bar) Pressure
ΔP
Pa or kPa (bar) differential pressure
q
litres per minute test flow rate
q litres per minute average test flow rate
q litres per minute minimum test flow rate (25 % of q )
min max
q litres per minute maximum test flow rate
max
q litres per minute discarded downstream sample flow rate
d
litres per minute average injection flow rate
q
i
'
litres per minute desired injection flow rate
q
i
litres per minute discarded upstream sample flow rate
q
u
t
minutes test time
t minutes predicted test time
pr
minutes final test time
t
f
a
The subscript (c) signifies that the filtration ratio, α , and the average filtration ratio, α , are determined in
x()c x()c
accordance with the method in this document using automatic particle counters calibrated in accordance with ISO 11171.
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ISO 23369:2022(E)
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Symbol Unit Description
minutes test time at element differential pressure
t
P
seconds fall ramp time
t
F
seconds rise ramp time
t
R
′ seconds predicted test time
t
V litres final measured injection system volume
if
litres initial measured injection system volume
V
ii
V litres minimum required operating injection system volume
min
litres final measured filter test system volume
V
tf
V litres minimum validated injection system volume
v
micrometres particle sizes
xx,
12
x micrometres interpolated particle size
int
a
The subscript (c) signifies that the filtration ratio, α , and the average filtration ratio, α , are determined in
x()c x()c
accordance with the method in this document using automatic particle counters calibrated in accordance with ISO 11171.
5 General procedure
5.1 Set up and maintain apparatus in accordance with Clauses 6 and 7.
5.2 Validate equipment in accordance with Clause 8.
5.3 Run all tests in accordance with Clauses 9, 10 and 11.
5.4 Analyse test data in accordance with Clause 12.
5.5 Present data from Clauses 10, 11 and 12 in accordance with the requirements of Clause 13.
6 Test equipment
6.1 Calibrated timer, a digital or mechanical stopwatch calibrated by a facility meeting the
requirements of ISO/IEC 17025.
6.2 Automatic particle counter(s) (APC), calibrated in accordance with ISO 11171.
6.3 ISO medium test dust (ISO MTD) (in accordance with ISO 12103-1, A3 medium test dust), dried
at 110 °C to 150 °C for not less than 1 h for quantities less than 200 g. For use in the test system, mix the
test dust into the test fluid, mechanically agitate, then disperse ultrasonically in an ultrasonic bath that
2 2
has a power density of 3 000 W/m to 10 000 W/m .
For quantities greater than 200 g, dry for at least 30 min per additional 100 g. For use in the test system,
mix the test dust into the test fluid, mechanically agitate, then disperse ultrasonically with a power
2 2
density of 3 000 W/m to 10 000 W/m .
NOTE 1 This dust is commercially available. For availability of ISO medium test dust, contact the ISO Central
Secretariat or member bodies of ISO.
6.4 Online particle counting system (if necessary) with optional dilution system that has been
validated in accordance with ISO 11943.
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ISO 23369:2022(E)
6.5 Sample bottles, containing less than 20 particles larger than 6 µm(c) per millilitre of bottle
volume, qualified in accordance with ISO 3722, to collect samples for gravimetric analyses.
6.6 Petroleum base test fluid, with properties as specified in Annex A.
NOTE 1 The use of this hydraulic fluid ensures greater reproducibility of results and is based upon current
practices, other accepted filter standards and its world-wide availability.
NOTE 2 The addition of an anti-static agent to this test fluid can affect the test results.
6.7 Filter performance test circuit, composed of a filter test system and a contaminant injection
system.
6.7.1 Filter test system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rates, pressures and volumes required by the procedure and
capable of meeting the validation requirements of Clause 8;
b) a clean-up filter capable of providing an initial system contamination level as specified in Table 3;
c) a configuration that is relatively insensitive to the intended contaminant level and capable of
meeting the validation requirements of Clause 8;
d) a configuration that does not alter the test contaminant particle size distribution over the
anticipated test duration and that is capable of meeting the validation requirements of Clause 8;
e) pressure taps in accordance with the requirements of ISO 3968;
f) fluid sampling sections upstream and downstream of the test filter, in accordance with the
requirements of ISO 4021;
g) cyclic flow bypass line equipped with an automatically controlled shut-off valve (e.g., an electrically-
actuated ball valve or poppet type valve or alternative system (e.g., direct drive), which have been
shown to be satisfactory for this application) capable of producing the required flow rate cycle at
the designated frequency.
NOTE For typical configurations that have proved to be satisfactory, see the filter test system design guide
in Annex B.
6.7.2 Contaminant injection system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rates, pressures and volumes required by the procedure and
capable of meeting the validation requirements of Clause 8;
b) a configuration that is relatively insensitive to the intended contaminant level and capable of
meeting the validation requirements of Clause 8;
c) a configuration that does not alter the test contaminant particle size distribution over the
anticipated test duration and capable of meeting the validation requirements of Clause 8;
d) a fluid sampling section in accordance with the requirements of ISO 4021.
NOTE For typical configurations that have proved to be satisfactory, see the contaminant injection system
design guide in Annex B.
6.8 Membrane filters and associated equipment, suitable for conducting gravimetric
contamination analysis in accordance with ISO 4405.
6
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ISO 23369:2022(E)
7 Measurement accuracy and test condition variation
7.1 Use and maintain instrument accuracy and test conditions within the limits given in Table 2.
Table 2 — Instrument accuracy and test condition variation
Instrument accu- Allowed test condition
Test parameter SI unit
racy (±) of reading variation (±)
Conductivity pS/m 10 % 1 500 pS/m ± 500 pS/m
Differential pressure Pa or kPa (bar) 5 % —
Base upstream gravimetric level mg/L — 10 %
Injection flow rate mL/min 2 % 5 %
Test flow rate L/min 2 % 5 %
a
APC sensor and dilution flow rates mL/min 1,5 % 3 %
b 2 2
Kinematic viscosity mm /s 2 % 1 mm /s
Mass g 0,1 mg —
c
Temperature °C 1 °C 2 °C
Time s 0,1 s —
Injection system volume L 2 % —
Filter test system volume L 2 % 5 %
a
Sensor flow variation to be included in the overall 10 % allowed between sensors.
b 2
1 mm /s = 1 cSt
c
Or as required to guarantee the viscosity tolerance.
7.2 Maintain specific test parameters within the limits given in Table 3, depending on the test
condition being conducted.
Table 3 — Test condition values
Filter test condition
Parameter
Condition 1 Condition 2 Condition 3
Initial contamination level for filter test Less than 1 % of the minimum level specified in ISO 11943:2021,
system Table C.2 measured at the smallest particle size to be counted.
Initial contamination level for injection
Less than 1 % of injection gravimetric level.
system
Base upstream gravimetric level, based on
(3 ± 0,3) mg/L (10 ± 1,0) mg/L (15 ± 1,5) mg/L
a
the average test flow rate while cycling, q
Minimum of five sizes selected to cover the presumed filter
b performance range from α = 2 to α = 1 000. Typical sizes
Recommended particle sizes to be counted x()c x()c
are: (4, 5, 6, 7, 8, 10, 12, 14, 20, 25, 30) µm(c).
Sampling and counting method Online automatic particle counting
From q to q at a frequency of 0,1 Hz (6 cycles/min) in
max min
Cyclic flow rate conditions
accordance with the waveform specified in Figure 2.
a
When comparing test results between two filters, the base upstream gravimetric level and the wave form shall be the
same.
b
Particle sizes where α is low (α = 2, 10…) can be unobtainable for fine filters, and particle sizes where α is high
(α = 200, 1 000) can be unobtainable for coarser filters.
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ISO 23369:2022(E)
8 Filter performance test circuit validation procedures
8.1 General
These validation procedures reveal the effectiveness of the filter performance test circuit to maintain
contaminant entrainment and prevent contaminant size modification.
8.2 Filter test system validation
8.2.1 Install a conduit in place of the filter housing during validation. The conduit shall be selected so
that is produces the maximum differential pressure expected during testing.
NOTE An orifice with a 60° inlet and outlet is recommended.
8.2.2 Validation shall be performed at the cyclic flow rate that includes the lowest minimum test flow
rate ( q ) and highest maximum test flow rate ( q ) at which the filter test system is to be operated.
min max
The minimum test flow rate shall be 25 % of the maximum test flow rate.
8.2.3 Validate the cyclic flow at 0,1 Hz (6 cycles/min), unless otherwise specified.
8.2.4 Adjust the total fluid volume of the filter test system (exclusive of the clean-up filter circuit)
such that it is numerically within the range of 25 % to 50 % of the maximum volume flow rate, with a
minimum of 5 L.
It is recommended that the system be validated with a fluid volume numerically equal to 50 % of the
maximum test volume flow rate for flow rates less than or equal to 60 L/min, or 25 % of the maximum
test volume flow
...
2022-01-11
Date: 2021-12-21
Reference number of document: ISO/FDIS 23369 2022(E)
Committee identification: Date: 2022-08-02
ISO/TC 131/SC 6
Secretariat: BSI
Hydraulic fluid power — Multi-pass method of evaluating filtration performance of a filter element
under cyclic flow conditions
Transmissions hydrauliques — Évaluation des performances d'un élément filtrant par la méthode de filtration
multi-passe sous débit cyclique
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no
part of this publication may be reproduced or utilized otherwise in any form or by any means,
electronic or mechanical, including photocopying, or posting on the internet or an intranet, without
prior written permission. Permission can be requested from either ISO at the address below or ISO's
member body in the country of the requester.
ISO Copyright Office
CP 401 • CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
---------------------- Page: 2 ----------------------
ISO/FDIS 23369:2022(E)
Contents
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 4
5 General procedure . 5
6 Test equipment . 5
7 Measurement accuracy and test condition variation . 7
8 Filter performance test circuit validation procedures . 8
8.1 General . 8
8.2 Filter test system validation . 8
8.3 Contaminant injection system validation . 9
9 Summary of information required prior to testing a filter element . 10
10 Preliminary test preparation . 10
10.1 Test filter assembly . 10
10.2 Contaminant injection system . 11
10.3 Filter test system . 12
11 Filter performance test . 13
12 Calculations
13 Data presentation . 18
14 Identification statement (reference to this document) . 19
Annex A (normative) Base test fluid properties . 20
Annex B (informative) Test system design guide . 22
Annex C (informative) Example report, calculations and graphs . 27
Bibliography . 36
Foreword . v
Introduction . vi
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ISO/FDIS 23369:2022(E)
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 4
5 General procedure . 6
6 Test equipment . 6
7 Measurement accuracy and test condition variation . 8
8 Filter performance test circuit validation procedures . 9
8.1 General . 9
8.2 Filter test system validation . 9
8.3 Contaminant injection system validation . 10
9 Summary of information required prior to testing a filter element . 11
10 Preliminary test preparation . 11
10.1 Test filter assembly . 11
10.2 Contaminant injection system . 12
10.3 Filter test system . 13
11 Filter performance test . 14
12 Calculations . 17
13 Data presentation . 20
14 Identification statement (reference to this document) . 21
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ISO/FDIS 23369:2022(E)
Annex A (normative) Base test fluid properties . 22
Annex B (informative) Test system design guide . 24
Annex C (informative) Example report, calculations and graphs . 30
Bibliography . 42
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ISO/FDIS 23369:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on the
ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
This second edition cancels and replaces the first edition (ISO 1688923369:2021), which has been
technically revised.
The main changes compared to the previous edition are as follows:
— calculation of ramp time.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iivi © ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 23369:2022(E)
Introduction
In hydraulic fluid power systems, one of the functions of the hydraulic fluid is to separate and lubricate the
moving parts of components. The presence of solid particulate contamination produces wear, resulting in
loss of efficiency, reduced component life and subsequent unreliability.
A hydraulic filter is provided to control the number of particles circulating within the system to a level that
is commensurate with the degree of sensitivity of the components to contaminants and the level of
reliability required by the users.
Test procedures enable the comparison of the relative performance of filters so that the most appropriate
filter can be selected. The performance characteristics of a filter are a function of the element (its medium
and geometry) and the housing (its general configuration and seal design).
In practice, a filter is subjected to a continuous flow of contaminant entrained in the hydraulic fluid until
some specified terminal differential pressure (relief-valve cracking pressure of differential-pressure
indicator setting) is reached.
Both the length of operating time (prior to reaching terminal pressure) and the contaminant level at any
point in the system are functions of the rate of contaminant addition (ingression plus generation rates) and
the performance characteristics of the filter.
Therefore, a realistic laboratory test establishes the relative performance of a filter by providing the test
filter with a continuous supply of ingressed contaminant and allowing the periodic monitoring of the
filtration performance characteristics of the filter. A standard multi-pass method for evaluating the
performance of hydraulic fluid power filter elements under steady-state flow conditions has been
developed as ISO 16889. That test procedure provides a basis for the comparison of the relative
performance characteristics of various filter elements. The results from such a test, however, might not be
directly applicable to most actual operating conditions.
In actual operation, a hydraulic fluid power filter is generally not subjected to steady-state flow but to
varying degrees of cyclic flow. Tests have shown that, in many instances, the filtration capabilities of an
element are severely reduced when subjected to varying cyclic flow conditions. It is therefore important to
evaluate the filtration performance of a filter for applications under cyclic flow conditions.
The cyclic flow multi-pass test procedure for hydraulic filters specified in this document has been
developed to supplement the basic steady-state flow test (ISO 16889) for filter elements that are expected
to be placed in service with cyclic flow. The recommended flow cycle rate of 0,1 Hz is a result of an
industry survey and a broad range of test results. If much higher cycle rates are expected in actual service,
the test should be conducted at that frequency to produce more meaningful results. The procedure
specified in this document may be applied at a cycle rate other than 0,1 Hz, if agreed upon between the
supplier and user. However, only values resulting from testing at the 0,1 Hz cycle rate may be reported as
having been determined in accordance with this document.
Fluid samples are extracted from the test system to evaluate the filter element’s particulate removal
characteristics. To prevent this sampling from adversely affecting the test results, a lower limit is placed
upon the rated flow rate of filter elements that should be tested with this procedure.
The current maximum flow rate specified in this document is based upon the maximum gravimetric level
of injection systems that have been qualified to date.
© ISO 2022 – All rights reserved vii
---------------------- Page: 7 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD
ISO/FDIS 23369:2022(E)
Hydraulic fluid power — Multi-pass method of evaluating filtration performance of a filter element
under cyclic flow conditions
1 Scope
This document specifies:
a) A multi-pass filtration performance test under cyclic flow conditions with continuous contaminant
injection for hydraulic fluid power filter elements.
b) A procedure for determining the contaminant capacity, particulate removal and differential pressure
characteristics.
c) A test currently applicable to hydraulic fluid power filter elements that exhibit an average filtration
ratio greater than or equal to 75 for particle sizes ≤ ≤25 µm(c), and a final test system reservoir
gravimetric level of less than 200 mg/L. It is necessary to determine by validation the range of flow
rates and the lower particle size limit that can be used in test facilities.
d) A test using ISO 12103-1 A3 medium test dust contaminant and a test fluid.
This document provides a test procedure that yields reproducible test data for appraising the filtration
performance of a hydraulic fluid power filter element without influence of electrostatic charge.
This document is applicable to three test conditions:
1) Base upstream gravimetric level of 3 mg/L.
2) Base upstream gravimetric level of 10 mg/L.
3) Base upstream gravimetric level of 15 mg/L.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2160, Petroleum products — Corrosiveness to copper — Copper strip test
ISO 2942, Hydraulic fluid power — Filter elements — Verification of fabrication integrity and determination
of the first bubble point
ISO 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods
ISO 3968, Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow
ISO 4021, Hydraulic fluid power — Particulate contamination analysis — Extraction of fluid samples from
lines of an operating system
ISO 4405, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the gravimetric method
© ISO 2022 – All rights reserved 11
---------------------- Page: 8 ----------------------
ISO/FDIS 23369:2022(E)
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
ISO 11943:2021, Hydraulic fluid power — Online automatic particle-counting systems for liquids — Methods
of calibration and validation
ISO 12103-1, Road vehicles — Test contaminants for filter evaluation — Part 1: Arizona test dust
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
contaminant mass injected
m
i
mass of specific particulate contaminant injected into the test circuit to obtain the terminal differential
pressure
3.2
differential pressure
difference between the tested component inlet and outlet pressures as measured under the specified
conditions
Note 1 to entry: See Figure 1 for a graphical depiction of differential pressure terms.
3.3
clean assembly differential pressure
difference between the tested component inlet and outlet pressures as measured with a clean filter
housing containing a clean filter element
3.4
clean element differential pressure
differential pressure of the clean element calculated as the difference between the clean assembly
differential pressure (3.3) and the housing differential pressure (3.6)
3.5
final assembly differential pressure
assembly differential pressure at the end of a test, equal to the sum of the housing differential pressure
and the terminal element differential pressure
3.6
housing differential pressure
differential pressure of the filter housing without an element
3.7
terminal element differential pressure
22 © ISO 2022 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/FDIS 23369:2022(E)
maximum differential pressure across the filter element as designated by the manufacturer to limit useful
performance
3.8
rest conductivity
electrical conductivity at the initial instant of current measurement after a DC voltage is impressed
between electrodes
Note 1 to entry: Rest conductivity is the reciprocal of the resistance of uncharged fluid in the absence of ionic
depletion or polarization.
3.9
retained capacity
m
R
mass of specific particulate contaminant effectively retained by the filter element when terminal element
differential pressure is reached
3.10
cyclic flow
change of flow from the specified rated flow rate to 25 % of rated flow rate at a specified frequency and
waveform
© ISO 2022 – All rights reserved 33
---------------------- Page: 10 ----------------------
ISO/FDIS 23369:2022(E)
Key
differential pressure (∆𝑃𝑃) (∆P) )
1 Field Code Changed
2 test time or contaminant mass injected
3 final assembly differential pressure (end of test)
4 terminal element differential pressure
clean element differential pressure at q q
Field Code Changed
5
max max
housing differential pressure at q q
6 Field Code Changed
max max
clean assembly differential pressure at
q q Field Code Changed
7
max max
Figure 1 — Differential pressure conventions for multi-pass test under cyclic flow conditions
4 Symbols
Table 1 — Symbols
Symbol Unit Description
particles per millilitre overall average upstream count of particles larger than size x x
A Field Code Changed
A
u,x
u,x
Field Code Changed
particles per millilitre overall average downstream count of particles larger than size x x
A A
d,x d,x
Field Code Changed
a
– filtration ratio at particle size x x (ISO 11171 calibration)
Field Code Changed
α
x(c)
Field Code Changed
a
α
x(c)
Field Code Changed
– filtration ratio at particle size x x and time interval t
α α Field Code Changed
x ,t xt,
Field Code Changed
–
α α
average filtration ratio at particle size x x (ISO 11171 calibration)
x(c) x(c)
Field Code Changed
a a
litres per second
Field Code Changed
rise and fall ramp flow rate acceleration
squared
Field Code Changed
milligrams per litre average base upstream gravimetric level
c c
b b Field Code Changed
' ' milligrams per litre desired base upstream gravimetric level
Field Code Changed
c c
b
b
milligrams per litre average injection gravimetric level
c c
Field Code Changed
i i
' ' milligrams per litre desired injection gravimetric level
Field Code Changed
c
c
i
i
milligrams per litre test reservoir gravimetric level at 80 % assembly differential pressure
c c
Field Code Changed
80 80
m m
grams mass of contaminant needed for injection
Field Code Changed
grams estimated filter element contaminant capacity (mass injected)
m m
Field Code Changed
e e
grams contaminant mass injected
m m
Field Code Changed
i i
44 © ISO 2022 – All rights reserved
---------------------- Page: 11 ----------------------
ISO/FDIS 23369:2022(E)
grams contaminant mass injected at element differential pressure
m m
Field Code Changed
P P
grams retained capacity
m m
Field Code Changed
R R
N N – number of counts in specific time period
Field Code Changed
particles per millilitre number of upstream particles larger than size x x at count i i
N
Field Code Changed
u,xi,
N Field Code Changed
u,xi,
Field Code Changed
particles per millilitre number of downstream particles larger than size x x at count i i
N
d,xi,
Field Code Changed
N
d,xi,
Field Code Changed
particles per millilitre average upstream count of particles larger than size x x at time interval
N Field Code Changed
u,x ,t
t t
Field Code Changed
N
u,xt,
Field Code Changed
particles per millilitre average downstream count of particles larger than size x x at time
N
d,x ,t
Field Code Changed
interval t t
N
d,xt,
Field Code Changed
p p
Pa or kPa (bar) Pressure Field Code Changed
Field Code Changed
∆𝑃𝑃 ∆P Pa or kPa (bar) differential pressure
Field Code Changed
q q
litres per minute test flow rate
Field Code Changed
litres per minute average test flow rate
q q
Field Code Changed
litres per minute
q q minimum test flow rate (25 % of q q )
Field Code Changed
min max
min max
Field Code Changed
q q
litres per minute maximum test flow rate
max max
Field Code Changed
litres per minute discarded downstream sample flow rate
q q
d
d
Field Code Changed
litres per minute average injection flow rate
q q
Field Code Changed
i i
' ' litres per minute desired injection flow rate
Field Code Changed
q q
i
i
litres per minute discarded upstream sample flow rate
q q
Field Code Changed
u u
t t minutes test time
Field Code Changed
minutes predicted test time
t t Field Code Changed
pr pr
minutes final test time
t t
Field Code Changed
f f
minutes test time at element differential pressure
t t
Field Code Changed
P P
seconds fall ramp time
t t
Field Code Changed
F F
seconds rise ramp time
t t
Field Code Changed
R R
seconds predicted test time
t′ t ′
Field Code Changed
© ISO 2022 – All rights reserved 55
---------------------- Page: 12 ----------------------
ISO/FDIS 23369:2022(E)
litres final measured injection system volume
V V
Field Code Changed
if if
litres initial measured injection system volume
V V
Field Code Changed
ii ii
litres minimum required operating injection system volume
V V
Field Code Changed
min min
litres final measured filter test system volume
V V
Field Code Changed
tf tf
litres minimum validated injection system volume
V V
Field Code Changed
v v
micrometres particle sizes
xx,
12
xx,
1 2 Field Code Changed
micrometres interpolated particle size
x x
Field Code Changed
int int
a
The subscript (c) signifies that the filtration ratio, α α , and the average filtration ratio, α α , are determined
x(c) x(c) x(c) x(c) Field Code Changed
in accordance with the method in this document using automatic particle counters calibrated in accordance with ISO 11171.
Field Code Changed
5 General procedure
5.1 Set up and maintain apparatus in accordance with Clauses 6 and 7.
5.2 Validate equipment in accordance with Clause 8.
5.3 Run all tests in accordance with Clauses 9, 10 and 11.
5.4 Analyse test data in accordance with Clause 12.
5.5 Present data from Clauses 10, 11 and 12 in accordance with the requirements of Clause 13.
6 Test equipment
6.1 Calibrated timer, a digital or mechanical stopwatch calibrated by a facility meeting the requirements
of ISO/IEC 17025.
6.2 Automatic particle counter(s) (APC), calibrated in accordance with ISO 11171.
6.3 ISO medium test dust (ISO MTD) (in accordance with ISO 12103-1, A3 medium test dust), dried at
110 °C to 150 °C for not less than 1 h for quantities less than 200 g. For use in the test system, mix the test
dust into the test fluid, mechanically agitate, then disperse ultrasonically in an ultrasonic bath that has a
2 2
power density of 3 000 W/m to 10 000 W/m .
For quantities greater than 200 g, dry for at least 30 min per additional 100 g. For use in the test system,
mix the test dust into the test fluid, mechanically agitate, then disperse ultrasonically with a power density
2 2
of 3 000 W/m to 10 000 W/m .
NOTE 1 This dust is commercially available. For availability of ISO medium test dust, contact the ISO Central
Secretariat or member bodies of ISO.
66 © ISO 2022 – All rights reserved
---------------------- Page: 13 ----------------------
ISO/FDIS 23369:2022(E)
6.4 If necessary, an onlineOnline particle counting system (if necessary) with optional dilution system
that has been validated in accordance with ISO 11943.
6.5 Sample bottles, containing less than 20 particles larger than 6 µm(c) per millilitre of bottle volume,
qualified in accordance with ISO 3722, to collect samples for gravimetric analyses.
6.6 Petroleum base test fluid, with properties as specified in Annex A.
NOTE 1 The use of this hydraulic fluid ensures greater reproducibility of results and is based upon current
practices, other accepted filter standards and its world-wide availability.
NOTE 2 The addition of an anti-static agent to this test fluid can affect the test results.
6.7 Filter performance test circuit, composed of a filter test system and a contaminant injection system.
6.7.1 Filter test system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rates, pressures and volumes required by the procedure and
capable of meeting the validation requirements of Clause 8;
b) a clean-up filter capable of providing an initial system contamination level as specified in Table 3;
c) a configuration that is relatively insensitive to the intended contaminant level and capable of meeting
the validation requirements of Clause 8;
d) a configuration that does not alter the test contaminant particle size distribution over the anticipated
test duration and that is capable of meeting the validation requirements of Clause 8;
e) pressure taps in accordance with the requirements of ISO 3968;
f) fluid sampling sections upstream and downstream of the test filter, in accordance with the
requirements of ISO 4021;
g) cyclic flow bypass line equipped with an automatically controlled shut-off valve (e.g., an electrically-
actuated ball valve or poppet type valve or alternative system (e.g., direct drive), which have been
shown to be satisfactory for this application) capable of producing the required flow rate cycle at the
designated frequency.
NOTE For typical configurations that have proved to be satisfactory, see the filter test system design guide in
Annex B.
6.7.2 Contaminant injection system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rat
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23369
ISO/TC 131/SC 6
Hydraulic fluid power — Multi-
Secretariat: BSI
pass method of evaluating filtration
Voting begins on:
2022-09-16 performance of a filter element under
cyclic flow conditions
Voting terminates on:
2022-11-11
Transmissions hydrauliques — Évaluation des performances d’un
élément filtrant par la méthode de filtration multi-passe sous débit
cyclique
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 23369:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/FDIS 23369:2022(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23369
ISO/TC 131/SC 6
Hydraulic fluid power — Multi-
Secretariat: BSI
pass method of evaluating filtration
Voting begins on:
performance of a filter element under
cyclic flow conditions
Voting terminates on:
Transmissions hydrauliques — Évaluation des performances d’un
élément filtrant par la méthode de filtration multi-passe sous débit
cyclique
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
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DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
ISO/FDIS 23369:2022(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
© ISO 2022 – All rights reserved
NATIONAL REGULATIONS. © ISO 2022
---------------------- Page: 2 ----------------------
ISO/FDIS 23369:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 4
5 General procedure .5
6 Test equipment .5
7 Measurement accuracy and test condition variation . 7
8 Filter performance test circuit validation procedures . 8
8.1 General . 8
8.2 Filter test system validation . 8
8.3 Contaminant injection system validation . 9
9 Summary of information required prior to testing a filter element .9
10 Preliminary test preparation .10
10.1 Test filter assembly . 10
10.2 Contaminant injection system . . 10
10.3 Filter test system . 11
11 Filter performance test .12
12 Calculations .14
13 Data presentation .17
14 Identification statement (reference to this document) .18
Annex A (normative) Base test fluid properties .19
Annex B (informative) Test system design guide .21
Annex C (informative) Example report, calculations and graphs .26
Bibliography .35
iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/FDIS 23369:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and nongovernmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
This second edition cancels and replaces the first edition (ISO 23369:2021), which has been technically
revised.
The main changes are as follows:
— calculation of ramp time.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 23369:2022(E)
Introduction
In hydraulic fluid power systems, one of the functions of the hydraulic fluid is to separate and lubricate
the moving parts of components. The presence of solid particulate contamination produces wear,
resulting in loss of efficiency, reduced component life and subsequent unreliability.
A hydraulic filter is provided to control the number of particles circulating within the system to a level
that is commensurate with the degree of sensitivity of the components to contaminants and the level of
reliability required by the users.
Test procedures enable the comparison of the relative performance of filters so that the most
appropriate filter can be selected. The performance characteristics of a filter are a function of the
element (its medium and geometry) and the housing (its general configuration and seal design).
In practice, a filter is subjected to a continuous flow of contaminant entrained in the hydraulic fluid until
some specified terminal differential pressure (relief-valve cracking pressure of differential-pressure
indicator setting) is reached.
Both the length of operating time (prior to reaching terminal pressure) and the contaminant level at
any point in the system are functions of the rate of contaminant addition (ingression plus generation
rates) and the performance characteristics of the filter.
Therefore, a realistic laboratory test establishes the relative performance of a filter by providing the
test filter with a continuous supply of ingressed contaminant and allowing the periodic monitoring of
the filtration performance characteristics of the filter. A standard multi-pass method for evaluating
the performance of hydraulic fluid power filter elements under steady-state flow conditions has
been developed as ISO 16889. That test procedure provides a basis for the comparison of the relative
performance characteristics of various filter elements. The results from such a test, however, might not
be directly applicable to most actual operating conditions.
In actual operation, a hydraulic fluid power filter is generally not subjected to steady-state flow but
to varying degrees of cyclic flow. Tests have shown that, in many instances, the filtration capabilities
of an element are severely reduced when subjected to varying cyclic flow conditions. It is therefore
important to evaluate the filtration performance of a filter for applications under cyclic flow conditions.
The cyclic flow multi-pass test procedure for hydraulic filters specified in this document has been
developed to supplement the basic steady-state flow test (ISO 16889) for filter elements that are
expected to be placed in service with cyclic flow. The recommended flow cycle rate of 0,1 Hz is a result
of an industry survey and a broad range of test results. If much higher cycle rates are expected in
actual service, the test should be conducted at that frequency to produce more meaningful results. The
procedure specified in this document may be applied at a cycle rate other than 0,1 Hz, if agreed upon
between the supplier and user. However, only values resulting from testing at the 0,1 Hz cycle rate may
be reported as having been determined in accordance with this document.
Fluid samples are extracted from the test system to evaluate the filter element’s particulate removal
characteristics. To prevent this sampling from adversely affecting the test results, a lower limit is
placed upon the rated flow rate of filter elements that should be tested with this procedure.
The current maximum flow rate specified in this document is based upon the maximum gravimetric
level of injection systems that have been qualified to date.
v
© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23369:2022(E)
Hydraulic fluid power — Multi-pass method of evaluating
filtration performance of a filter element under cyclic flow
conditions
1 Scope
This document specifies:
a) A multi-pass filtration performance test under cyclic flow conditions with continuous contaminant
injection for hydraulic fluid power filter elements.
b) A procedure for determining the contaminant capacity, particulate removal and differential
pressure characteristics.
c) A test currently applicable to hydraulic fluid power filter elements that exhibit an average filtration
ratio greater than or equal to 75 for particle sizes ≤25 µm(c), and a final test system reservoir
gravimetric level of less than 200 mg/L. It is necessary to determine by validation the range of flow
rates and the lower particle size limit that can be used in test facilities.
d) A test using ISO 12103-1 A3 medium test dust contaminant and a test fluid.
This document provides a test procedure that yields reproducible test data for appraising the filtration
performance of a hydraulic fluid power filter element without influence of electrostatic charge.
This document is applicable to three test conditions:
1) Base upstream gravimetric level of 3 mg/L.
2) Base upstream gravimetric level of 10 mg/L.
3) Base upstream gravimetric level of 15 mg/L.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2160, Petroleum products — Corrosiveness to copper — Copper strip test
ISO 2942, Hydraulic fluid power — Filter elements — Verification of fabrication integrity and determination
of the first bubble point
ISO 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods
ISO 3968, Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow
ISO 4021, Hydraulic fluid power — Particulate contamination analysis — Extraction of fluid samples from
lines of an operating system
ISO 4405, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the gravimetric method
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
1
© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 23369:2022(E)
ISO 11943:2021, Hydraulic fluid power — Online automatic particle-counting systems for liquids —
Methods of calibration and validation
ISO 121031, Road vehicles — Test contaminants for filter evaluation — Part 1: Arizona test dust
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
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3.1
contaminant mass injected
m
i
mass of specific particulate contaminant injected into the test circuit to obtain the terminal differential
pressure
3.2
differential pressure
difference between the tested component inlet and outlet pressures as measured under the specified
conditions
Note 1 to entry: See Figure 1 for a graphical depiction of differential pressure terms.
3.3
clean assembly differential pressure
difference between the tested component inlet and outlet pressures as measured with a clean filter
housing containing a clean filter element
3.4
clean element differential pressure
differential pressure of the clean element calculated as the difference between the clean assembly
differential pressure (3.3) and the housing differential pressure (3.6)
3.5
final assembly differential pressure
assembly differential pressure at the end of a test, equal to the sum of the housing differential pressure
and the terminal element differential pressure
3.6
housing differential pressure
differential pressure of the filter housing without an element
3.7
terminal element differential pressure
maximum differential pressure across the filter element as designated by the manufacturer to limit
useful performance
3.8
rest conductivity
electrical conductivity at the initial instant of current measurement after a DC voltage is impressed
between electrodes
Note 1 to entry: Rest conductivity is the reciprocal of the resistance of uncharged fluid in the absence of ionic
depletion or polarization.
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ISO/FDIS 23369:2022(E)
3.9
retained capacity
m
R
mass of specific particulate contaminant effectively retained by the filter element when terminal
element differential pressure is reached
3.10
cyclic flow
change of flow from the specified rated flow rate to 25 % of rated flow rate at a specified frequency and
waveform
Key
1
differential pressure ΔP )
()
2 test time or contaminant mass injected
3 final assembly differential pressure (end of test)
4 terminal element differential pressure
5
clean element differential pressure at q
max
6
housing differential pressure at q
max
7
clean assembly differential pressure at q
max
Figure 1 — Differential pressure conventions for multi-pass test under cyclic flow conditions
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ISO/FDIS 23369:2022(E)
4 Symbols
Table 1 — Symbols
Symbol Unit Description
overall average upstream count of particles larger than size x
particles per millilitre
A
u,x
overall average downstream count of particles larger than size x
particles per millilitre
A
d,x
filtration ratio at particle size x (ISO 11171 calibration)
a
α –
x()c
filtration ratio at particle size x and time interval t
–
α
xt,
α –
average filtration ratio at particle size x (ISO 11171 calibration)
x()c
a
litres per second
rise and fall ramp flow rate acceleration
squared
milligrams per litre average base upstream gravimetric level
c
b
'
milligrams per litre desired base upstream gravimetric level
c
b
milligrams per litre average injection gravimetric level
c
i
'
milligrams per litre desired injection gravimetric level
c
i
milligrams per litre test reservoir gravimetric level at 80 % assembly differential pressure
c
80
m
grams mass of contaminant needed for injection
grams estimated filter element contaminant capacity (mass injected)
m
e
m grams contaminant mass injected
i
grams contaminant mass injected at element differential pressure
m
P
m grams retained capacity
R
N – number of counts in specific time period
particles per millilitre number of upstream particles larger than size x at count i
N
u,xi,
number of downstream particles larger than size x at count i
N particles per millilitre
d,xi,
average upstream count of particles larger than size x at time interval
particles per millilitre
N
u,xt,
t
average downstream count of particles larger than size x at time
particles per millilitre
N
d,xt,
interval t
p
Pa or kPa (bar) Pressure
ΔP
Pa or kPa (bar) differential pressure
q
litres per minute test flow rate
q litres per minute average test flow rate
q litres per minute minimum test flow rate (25 % of q )
min max
q litres per minute maximum test flow rate
max
q litres per minute discarded downstream sample flow rate
d
litres per minute average injection flow rate
q
i
'
litres per minute desired injection flow rate
q
i
litres per minute discarded upstream sample flow rate
q
u
t
minutes test time
t minutes predicted test time
pr
minutes final test time
t
f
a
The subscript (c) signifies that the filtration ratio, α , and the average filtration ratio, α , are determined in
x()c x()c
accordance with the method in this document using automatic particle counters calibrated in accordance with ISO 11171.
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ISO/FDIS 23369:2022(E)
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Symbol Unit Description
minutes test time at element differential pressure
t
P
seconds fall ramp time
t
F
seconds rise ramp time
t
R
′ seconds predicted test time
t
V litres final measured injection system volume
if
litres initial measured injection system volume
V
ii
V litres minimum required operating injection system volume
min
litres final measured filter test system volume
V
tf
V litres minimum validated injection system volume
v
micrometres particle sizes
xx,
12
x micrometres interpolated particle size
int
a
The subscript (c) signifies that the filtration ratio, α , and the average filtration ratio, α , are determined in
x()c x()c
accordance with the method in this document using automatic particle counters calibrated in accordance with ISO 11171.
5 General procedure
5.1 Set up and maintain apparatus in accordance with Clauses 6 and 7.
5.2 Validate equipment in accordance with Clause 8.
5.3 Run all tests in accordance with Clauses 9, 10 and 11.
5.4 Analyse test data in accordance with Clause 12.
5.5 Present data from Clauses 10, 11 and 12 in accordance with the requirements of Clause 13.
6 Test equipment
6.1 Calibrated timer, a digital or mechanical stopwatch calibrated by a facility meeting the
requirements of ISO/IEC 17025.
6.2 Automatic particle counter(s) (APC), calibrated in accordance with ISO 11171.
6.3 ISO medium test dust (ISO MTD) (in accordance with ISO 121031, A3 medium test dust), dried
at 110 °C to 150 °C for not less than 1 h for quantities less than 200 g. For use in the test system, mix the
test dust into the test fluid, mechanically agitate, then disperse ultrasonically in an ultrasonic bath that
2 2
has a power density of 3 000 W/m to 10 000 W/m .
For quantities greater than 200 g, dry for at least 30 min per additional 100 g. For use in the test system,
mix the test dust into the test fluid, mechanically agitate, then disperse ultrasonically with a power
2 2
density of 3 000 W/m to 10 000 W/m .
NOTE 1 This dust is commercially available. For availability of ISO medium test dust, contact the ISO Central
Secretariat or member bodies of ISO.
6.4 Online particle counting system (if necessary) with optional dilution system that has been
validated in accordance with ISO 11943.
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ISO/FDIS 23369:2022(E)
6.5 Sample bottles, containing less than 20 particles larger than 6 µm(c) per millilitre of bottle
volume, qualified in accordance with ISO 3722, to collect samples for gravimetric analyses.
6.6 Petroleum base test fluid, with properties as specified in Annex A.
NOTE 1 The use of this hydraulic fluid ensures greater reproducibility of results and is based upon current
practices, other accepted filter standards and its world-wide availability.
NOTE 2 The addition of an anti-static agent to this test fluid can affect the test results.
6.7 Filter performance test circuit, composed of a filter test system and a contaminant injection
system.
6.7.1 Filter test system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rates, pressures and volumes required by the procedure and
capable of meeting the validation requirements of Clause 8;
b) a clean-up filter capable of providing an initial system contamination level as specified in Table 3;
c) a configuration that is relatively insensitive to the intended contaminant level and capable of
meeting the validation requirements of Clause 8;
d) a configuration that does not alter the test contaminant particle size distribution over the
anticipated test duration and that is capable of meeting the validation requirements of Clause 8;
e) pressure taps in accordance with the requirements of ISO 3968;
f) fluid sampling sections upstream and downstream of the test filter, in accordance with the
requirements of ISO 4021;
g) cyclic flow bypass line equipped with an automatically controlled shut-off valve (e.g., an electrically-
actuated ball valve or poppet type valve or alternative system (e.g., direct drive), which have been
shown to be satisfactory for this application) capable of producing the required flow rate cycle at
the designated frequency.
NOTE For typical configurations that have proved to be satisfactory, see the filter test system design guide
in Annex B.
6.7.2 Contaminant injection system, consisting of:
a) a reservoir, pump, fluid conditioning apparatus and instrumentation that are capable of
accommodating the range of flow rates, pressures and volumes required by the procedure and
capable of meeting the validation requirements of Clause 8;
b) a configuration that is relatively insensitive to the intended contaminant level and capable of
meeting the validation requirements of Clause 8;
c) a configuration that does not alter the test contaminant particle size distribution over the
anticipated test duration and capable of meeting the validation requirements of Clause 8;
d) a fluid sampling section in accordance with the requirements of ISO 4021.
NOTE For typical configurations that have proved to be satisfactory, see the contaminant injection system
design guide in Annex B.
6.8 Membrane filters and associated equipment, suitable for conducting gravimetric
contamination analysis in accordance with ISO 4405.
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ISO/FDIS 23369:2022(E)
7 Measurement accuracy and test condition variation
7.1 Use and maintain instrument accuracy and test conditions within the limits given in Table 2.
Table 2 — Instrument accuracy and test condition variation
Instrument
Allowed test condition
Test parameter SI unit accuracy ( ± ) of
variation ( ± )
reading
Conductivity pS/m 10 % 1 500 pS/m ± 500 pS/m
Differential pressure Pa or kPa (bar) 5 % —
Base upstream gravimetric level mg/L — 10 %
Injection flow rate mL/min 2 % 5 %
Test flow rate L/min 2 % 5 %
a
APC sensor and dilution flow rates mL/min 1,5 % 3 %
b 2 2
Kinematic viscosity mm /s 2 % 1 mm /s
Mass g 0,1 mg —
c
Temperature °C 1 °C 2 °C
Time s 0,1 s —
Injection system volume L 2 % —
Filter test system volume L 2 % 5 %
a
Sensor flow variation to be included in the overall 10 % allowed between sensors.
b 2
1 mm /s = 1 cSt
c
Or as required to guarantee the viscosity tolerance.
7.2 Maintain specific test parameters within the limits given in Table 3, depending on the test
condition being conducted.
Table 3 — Test condition values
Filter test condition
Parameter
Condition 1 Condition 2 Condition 3
Initial contamination level for filter test Less than 1 % of the minimum level specified in ISO 11943:2021,
system Table C.2 measured at the smallest particle size to be counted.
Initial contamination level for injection
Less than 1 % of injection gravimetric level.
system
Base upstream gravimetric level, based on
(3 ± 0,3) mg/L (10 ± 1,0) mg/L (15 ± 1,5) mg/L
a
the average test flow rate while cycling, q
Minimum of five sizes selected to cover the presumed filter
b performance range from α = 2 to α = 1 000. Typical sizes
Recommended particle sizes to be counted x()c x()c
are: (4, 5, 6, 7, 8, 10, 12, 14, 20, 25, 30) µm(c).
Sampling and counting method Online automatic particle counting
From q to q at a frequency of 0,1 Hz (6 cycles/min) in
max min
Cyclic flow rate conditions
accordance with the waveform specified in Figure 2.
a
When comparing test results between two filters, the base upstream gravimetric level and the wave form shall be the
same.
b
Particle sizes where α is low (α
...
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