ISO 21018-1:2024
(Main)Hydraulic fluid power — Monitoring the level of particulate contamination of the fluid — Part 1: General principles
Hydraulic fluid power — Monitoring the level of particulate contamination of the fluid — Part 1: General principles
This document specifies methods and techniques that are applicable to the monitoring of particulate contamination levels in hydraulic systems that cannot be calibrated in accordance with ISO 11171. It also describes the relative merits of various techniques, so that the correct monitor for a given application can be selected. The techniques described in this document are suitable for monitoring: a) the general cleanliness level in hydraulic systems; b) the progress in flushing operations; c) support equipment and test rigs. This document can also be applicable for other liquids (e.g. lubricants, fuels and process liquids). NOTE Instruments used to monitor particulate contamination that cannot be calibrated according to ISO 11171 are not considered as or claimed to be particle counters, even if they use the same physical principles as particle counters
Transmissions hydrauliques — Surveillance du niveau de pollution particulaire des fluides — Partie 1: Principes généraux
L'ISO 21018-1:2008 spécifie les méthodes et les techniques applicables à la surveillance des niveaux de pollution particulaire des systèmes hydrauliques. Elle décrit aussi le bien-fondé des différentes techniques afin de pouvoir choisir le détecteur qui convient à une application donnée. Les techniques décrites dans l'ISO 21018-1:2008 permettent de surveiller le niveau de propreté général des systèmes hydrauliques, l'évolution des opérations de rinçage, les matériels auxiliaires et les montages d'essai. L'ISO 21018-1:2008 peut aussi être appliquée à d'autres fluides (par exemple les lubrifiants, les carburants et les fluides de procédé).
General Information
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Standards Content (Sample)
International
Standard
ISO 21018-1
Second edition
Hydraulic fluid power —
2024-10
Monitoring the level of particulate
contamination of the fluid —
Part 1:
General principles
Transmissions hydrauliques — Surveillance du niveau de
pollution particulaire des fluides —
Partie 1: Principes généraux
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Health and safety . 4
4.1 General .4
4.2 Electric power .4
4.3 Mechanical fluid power.4
4.4 Process liquids .4
4.4.1 Flammable or combustible liquids .4
4.4.2 Chemical compatibility .4
4.5 Electrical earthing/grounding .4
4.6 Environmental .4
5 Selection of monitoring technique. 5
5.1 General .5
5.2 Selection .5
6 Procedures and precautions . 5
6.1 General .5
6.2 Sampling .5
6.2.1 Obtaining representative samples .5
6.2.2 Off-line sampling .6
6.2.3 Off-line analysis .6
6.3 Analysis .6
6.3.1 On-line analysis .6
6.3.2 In-line analysis .6
6.3.3 Off-line analysis .7
6.4 Calibration procedures .7
6.5 Checking data repeatability .7
6.6 Training .8
6.7 Controlling the precision of the technique .8
7 Test report . 8
Annex A (informative) Summary of various technique attributes . 9
Annex B (informative) Description and relative merits of different contaminant monitoring
techniques .15
Bibliography .23
iii
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
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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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
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Any trade name used in this document is information given for the convenience of users and does not
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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 21018-1:2008), which has been technically
revised. The main changes are as follows:
— 3.1 contains an updated definition for automated particle counter;
— 3.2 contains an updated definition for particle contamination model;
— 3.10 contains an updated definition for mesh;
— 3.11 now contains a note for the particle size definition;
— B.8.1 has been updated to accurately describe the capabilities of image analysis.
A list of all parts in the ISO 21018 series can be found on the ISO website.
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
Introduction
In hydraulic fluid power systems, power is transmitted through a liquid under pressure within a closed
circuit. The liquid is both a lubricant and a power-transmitting medium. The presence of solid particulate
contamination in the liquid interferes with the ability of the hydraulic liquid to lubricate and causes wear
to the components. The extent of this form of contamination in the liquid has a direct bearing on the
performance and reliability of the system and it is necessary to control this to levels that are considered
appropriate for the system concerned. Hydraulic oil filters are used to control the amount of particulate
contamination to a level that is suitable for both the contaminant sensitivity of the system and the level of
reliability required by the user.
Operators of hydraulic equipment are gradually defining maximum particle concentration levels for
components, systems and processes. These are often referred to as the required cleanliness level (RCL). This
cleanliness level is obtained by sampling the hydraulic liquid and measuring the particulate contamination
level. If the contamination level is above the RCL, then corrective actions are necessary to reduce the
contamination level. To avoid taking unnecessary actions, which can often prove costly, precision in sampling
and measuring the particulate contamination level is required.
A comprehensive range of measurement equipment is available, but the instruments used are usually
laboratory-based. This often requires that the equipment is operated in a special environment by specialist
laboratories and this delays delivery of the test result to the user. To overcome this disadvantage, instruments
are being continuously developed to determine the particulate contamination level, either using equipment
that can be operated in or near the workplace or directly using on-line or in-line techniques. For equipment
operated in the workplace, direct traceability to national measurement standards can be inappropriate, or
irrelevant, as the instruments are used to monitor the general level of particulate contamination or to inform
the user of a significant change in the level. When a significant change in the particulate contamination level
is detected, the actual level is then usually qualified by using an approved particle-counting method. Also,
these monitors can have simplified circuitry compared to similar laboratory units and this means that they
can be less accurate and precise.
In addition, some instruments are designed to work on the “go/no-go” principle and their ability to rapidly
evaluate the cleanliness level has resulted in an increase in their usage both in the fluid power industry and
other markets. Unfortunately, the lack of a standardized method for their use, recalibration (if applicable)
and means of checking the output validity means that the variability in the measurement data is at a level
higher than is desirable.
This document has been developed to provide uniform and consistent procedures for instruments that are
used for monitoring the contamination levels in hydraulic systems, especially those where direct traceability
to national measurement standards is not possible or is not applicable.
v
International Standard ISO 21018-1:2024(en)
Hydraulic fluid power — Monitoring the level of particulate
contamination of the fluid —
Part 1:
General principles
1 Scope
This document specifies methods and techniques that are applicable to the monitoring of particulate
contamination levels in hydraulic systems that cannot be calibrated in accordance with ISO 11171. It also
describes the relative merits of various techniques, so that the correct monitor for a given application can be
selected.
The techniques described in this document are suitable for monitoring:
a) the general cleanliness level in hydraulic systems;
b) the progress in flushing operations;
c) support equipment and test rigs.
This document can also be applicable for other liquids (e.g. lubricants, fuels and process liquids).
NOTE Instruments used to monitor particulate contamination that cannot be calibrated according to ISO 11171
are not considered as or claimed to be particle counters, even if they use the same physical principles as particle
counters
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 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods
ISO 4021, Hydraulic fluid power — Particulate contamination analysis — Extraction of fluid samples from lines
of an operating system
ISO 4406, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles
ISO 5598, Fluid power systems and components — Vocabulary
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
ISO 11500, Hydraulic fluid power — Determination of the particulate contamination level of a liquid sample by
automatic particle counting using the light-extinction principle
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 terms and definitions given in ISO 5598, ISO 11171 and the
following 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
automatic particle counter
APC
instrument that automatically:
a) senses individual particles suspended in a controlled volume of fluid using optical light extinction or
light scattering principles;
b) measures the size of particles;
c) sorts or compiles particles into size ranges;
d) counts particles in each size range;
e) reports the number of particles in each size range per unit volume; and
f) facilitates instrument calibration according to this document.
Note 1 to entry: APC used for particle size (3.11) determination with hydraulic fluids, aviation and diesel fuels, engine
oil and other petroleum-based fluids shall be calibrated per the requirements of ISO 11171.
[SOURCE: ISO 11171:2022, 3.1]
3.2
particle contamination monitor
PCM
instrument that automatically measures the concentrations of particles suspended in a fluid at certain sizes
and cannot be calibrated in accordance with ISO 11171, and whose output may be as a particle size (3.11)
distribution at limited sizes or as a contamination code
[SOURCE: ISO 21018-4:2019, 3.3]
3.3
coincidence error
error resulting from the presence of more than one particle in the sensing volume at one time
3.4
dynamic range
ratio of the largest and smallest particle size (3.11) that a sensor can analyse
3.5
filter media
filtration material that removes and retains particles as the fluid passes through
3.6
gel
semi-solid material that lacks a specific shape and can interfere with the counting or monitoring process
Note 1 to entry: Gels are usually formed by chemical reaction with the hydraulic liquid.
3.7
in-line analysis
analysis of a fluid sample of the liquid by an instrument that is permanently connected to a working flow
line and where all the liquid in that line passes through the sensor
3.8
off-line analysis
analysis of a fluid sample by an instrument that is not directly connected to the hydraulic system
3.9
on-line analysis
analysis performed on a fluid supplied directly to the instrument by a continuous line from the hydraulic system
Note 1 to entry: The instrument can be either permanently connected to the flow line or connected prior to analysis.
3.10
mesh
type of filter media (3.5) with a uniform pore structure that is made by weaving strands of wire or material
filaments, or fabricated directly
3.11
particle size
characteristic dimension of a particle that defines the magnitude of the particle in terms of a physically
measurable dimension related to the analysis technique used, such as the longest dimension or the
equivalent spherical diameter
Note 1 to entry: For automatic particle counters and light extinction particle contamination monitors, ISO 11171
defines particle size as the projected area equivalent diameter of particles. The equivalent diameter is determined by
NIST using scanning electron microscopy traceable through a NIST length standard or an APC calibrated according to
ISO 11171.
3.12
pore size
equivalent diameter of the holes in filter media (3.5) as determined by direct microscopic measurement or
calculated from permeability data
3.13
qualitative data
data that have less precision or accuracy than quantitative methods and usually give results in ranges rather
than exact numbers
3.14
quantitative data
data in the form of an exact numerical value of a parameter
3.15
required cleanliness level
RCL
hydraulic fluid cleanliness level required for a system, process or specification
[SOURCE: ISO 12669:2017, 3.9, modified — Note to entry has been omitted.]
3.16
silt
very small particles (< 3 µm in size) that are present in the liquid, often below the minimum detection size of
the technique used
Note 1 to entry: Silt can interfere with the effectiveness of the instrument either by obscuring particles or by
coincidence error effects.
Note 2 to entry: They can be small wear particles or products of hydraulic liquid degradation.
3.17
suction (sip) sampling
process of drawing a sample from a reservoir using a vacuum
3.18
suction (sip) analysis
analysis of a sample drawn by instrument pump from a non-pressurized container and delivered to the
instrument sensor
4 Health and safety
4.1 General
Operate the instrument in accordance with the manufacturer’s instructions and follow local health and
safety procedures at all times. Personal protective equipment shall be used when required.
4.2 Electric power
Take care when connecting the instrument to an electrical power source and follow the manufacturer's
instructions.
4.3 Mechanical fluid power
Instrument connections to pressurized lines shall be in accordance with the instrument manufacturer’s
instructions and in such a manner that the connection is secure and leak free. Any connectors used shall be
suitable for the pressure at the point of sampling.
Ensure that internal pressure has been dissipated before taking off any fittings or closures.
NOTE See Clause 6 for guidance regarding sampling from pressurized lines.
4.4 Process liquids
4.4.1 Flammable or combustible liquids
If test liquids are flammable or combustible, they shall be used as follows:
a) in accordance with all local requirements;
b) in accordance with the relevant material safety data sheet (SDS).
The transfer of volatile liquids from one container to another container shall be carried out carefully due to
the risk of sparking.
NOTE Follow the precautions for safe handling and usage described in the safety data sheet(s) of all fluids.
4.4.2 Chemical compatibility
Ensure that all chemicals and fluids used in the various processes are chemically compatible with each other
and with any equipment used.
4.5 Electrical earthing/grounding
Apparatus used for filtering or dispensing solvents or any volatile flammable liquid shall be electrically
earthed to avoid the risk of static discharge.
4.6 Environmental
All liquids and substances shall be disposed of in accordance with local environmental procedures.
Spillage shall be cleaned-up as detailed in the relevant SDS.
5 Selection of monitoring technique
5.1 General
The choice of instrument, or monitoring technique, depends upon, but is not limited to, the following aspects:
a) how the instrument is to be used, i.e. the mode of operation (A.2.4);
b) the purpose for which the analysis is required (A.2.2);
c) the parameter(s) to be measured (A.2.3);
d) the properties of the liquid (A.2.5).
5.2 Selection
Select the instrument and monitoring technique by considering the operational parameters detailed in
Annex A and Annex B, and choose a combination that satisfies the individual requirements for monitoring.
NOTE A.1, explains the modes of operation and analysis and A.2, gives guidance on the various aspects to consider
during selection and includes a selection matrix. Annex B gives a brief explanation of the different techniques and
their advantages and disadvantages.
6 Procedures and precautions
6.1 General
Whichever monitoring or measurement technique is selected, there are a number of precautions that shall
be taken to ensure that valid data are produced and errors are minimized.
This document gives general procedures that limit errors. Precautions relating to a specific technique are
given in the relevant part of the ISO 21018 series.
6.2 Sampling
6.2.1 Obtaining representative samples
6.2.1.1 Select the sampling position consistent with the reasons for sampling (see ISO 4021).
NOTE 1 It is extremely important to use the correct sampling technique(s). The use of equipment connected to or
mounted in or on the active flow line reduces the errors associated with extraneous contamination.
NOTE 2 The particulate contamination added to the sample from the sampling process can be much higher than the
particulate concentration that exists in the liquid of some filtered systems.
The guidelines described in 6.2.2 to 6.2.3 are typical good practice for obtaining reliable results and should
be read in conjunction with ISO 4021.
6.2.1.2 Use sampling valves that conform to ISO 4021.
6.2.1.3 For general monitoring, take the sample when the system is running and conditions are stable.
Sampling 30 min after start-up is suitable.
6.2.1.4 For periodic monitoring of a machine or process, take repeat samples from the same place, in
the same manner, when the machine or process is running normally and when operating conditions have
stabilized.
6.2.2 Off-line sampling
6.2.2.1 Use sample bottles that have been cleaned and verified in accordance with ISO 3722.
6.2.2.2 Site the sampling valve consistent with the reason for sampling.
6.2.2.3 Position the sampling valve in a location where good mixing conditions exist.
6.2.2.4 Flush the sampling valve and transfer line at a flow rate of at least 2 l/min with a minimum flushing
volume of 500 ml. Use higher flushing volumes (1 l to 3 l) if:
a) valves do not conform to the requirements of ISO 4021;
b) long transfer lines are used;
c) the system liquid is expected to be clean (i.e. ≤ 14/12/9 in accordance with ISO 4406).
6.2.2.5 Take the sample in a manner that minimizes the ingress of environmental contamination.
6.2.2.6 Cap the sample immediately after it is taken and label with a unique identification.
6.2.2.7 Do not take samples from drain valves.
6.2.3 Off-line analysis
6.2.3.1 Take the sample from a location where the liquid is in motion.
6.2.3.2 Shake and mix well the contents of containers before extracting the sample.
NOTE This method is the least-favoured option as the potential for errors and variability is greatest.
If mixing the contents of a bulk container is impractical, a note shall be made in the report.
6.2.3.3 Clean the area(s) surrounding the location where the sample is taken so that contamination does
not fall into the sample, the container or reservoir.
6.2.3.4 Flush the sampling system with at least 10 complete volumes (instrument and connecting pipes)
utilizing fluid from the system being tested.
6.3 Analysis
6.3.1 On-line analysis
6.3.1.1 Use sampling valves and procedures defined in ISO 4021.
6.3.1.2 Provide sufficient supply pressure to avoid instrument starvation or cavitation.
6.3.1.3 Flush the sampling lines with a minimum of 1 l of liquid sample after connection and before
analysis.
6.3.2 In-line analysis
Install the sensor in a location where the fluid is well mixed.
6.3.3 Off-line analysis
6.3.3.1 Follow ISO 11500 for off-line sample analysis.
NOTE Suction (sip) samples are frequently analysed off-line.
6.3.3.2 Continue the analysis until the data from two successive samples satisfy one of the following
requirements.
a) The results are within the limits set by the instrument manufacturer.
b) The difference in test results is less than 10 % of the mean of consecutive results at the smallest particle
size being monitored if the required output is particle count.
c) The same contamination code in accordance with ISO 4406 is recorded.
6.4 Calibration procedures
Although the principle of calibration may not apply to some techniques, the requirements and principles
of International Standards for measurement traceability shall be followed for applicable techniques. For
instance, where the instruments are automatic, they shall be calibrated or checked using ISO 12103-1 A3
medium test dust. In this way, any differences in the data measured using automatic particle counters (APC)
calibrated using either ISO 11171 or ISO 11943 and data from those monitors calibrated/checked with
suspensions of ISO 12103-1 A3 medium test dust in oil are minimized.
6.5 Checking data repeatability
6.5.1 Develop a means of checking the data to ensure the prompt detection of errors before reporting the
data. Use the procedures detailed below, as appropriate.
6.5.2 For automatic instruments, repeat the analysis until two successive data sets satisfy one of the
following conditions.
a) The results are within the limits set by the instrument manufacturer.
b) The difference in test results is less than 10 % of the mean of consecutive results at the smallest particle
size being monitored if the required output is particle count.
c) The same ISO 4406 code is recorded.
6.5.3 Review the test data and confirm that they are of the same order as:
a) previous data obtained from the same system or process;
b) previous data obtained from a similar system(s) using the same filtration level.
6.5.4 For off-line instruments where the sample is collected in a sample bottle, examine the sample for
conditions that can interfere with the effectiveness of the instrument, such as the ones given in a) to d).
a) The presence of large particles that can block small passageways, orifices or the sensor in the instrument.
The presence of large particles can also indicate the presence of high numbers of smaller particles.
b) Test-liquid cloudiness, which can indicate the presence of another liquid such as water in oil, oil in water-
based liquids, mixtures of liquids, etc., and which can interfere with instruments using the transmission
of light to detect particles.
c) A clear but dark appearance in a test liquid, which often indicates the presence of finely divided particles
(e.g. wear debris or oxidation products). The presence of finely divided particles in the test liquid can
interfere with the effectiveness of the test instrument due to coincidence error effects.
d) The presence of air bubbles in the test liquid, which interferes with the passage of light. Remove air
bubbles in accordance with ISO 11500 before any analysis is performed.
6.6 Training
Train operators both in the technique and in the specific instr
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