ISO 4406:2021

INTERNATIONAL ISO
STANDARD 4406
Fourth edition
2021-01
Hydraulic fluid power — Fluids
— Method for coding the level of
contamination by solid particles
Transmissions hydrauliques — Fluides — Méthode de codification du
niveau de pollution particulaire solide
Reference number
ISO 4406:2021(E)
©
ISO 2021

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ISO 4406:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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 © ISO 2021 – All rights reserved

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ISO 4406:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Code definitions. 1
4.1 General . 1
4.2 Basis of code . 2
4.3 Allocation of scale numbers . 2
4.4 Determination of code using automatic particle counter analysis . 3
4.5 Determination of code using microscope sizing . 4
5 Identification statement (reference to this document) . 4
Annex A (normative) Graphical presentation of the code number . 5
© ISO 2021 – All rights reserved iii

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ISO 4406:2021(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 fourth edition cancels and replaces the third edition (ISO 4406:2017), which has been technically
revised.
The main change compared to the previous edition is as follows:
— the use of Particle Contamination Monitors (PCMs) can also be utilized for the determination of the
ISO 4406 contamination code (see subclause 4.4.1) and PCM is referenced throughout this document.
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 2021 – All rights reserved

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ISO 4406:2021(E)

Introduction
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure
within an enclosed circuit. Solid particle contaminant is always present in the hydraulic fluid and the
amount needs to be determined because the contaminant can cause serious problems.
The ISO 4406 cleanliness code has gained world-wide acceptance as a means of communicating the
cleanliness of a hydraulic fluid. Most hydraulic component manufacturers require a certain ISO
cleanliness level for warranty purposes, to ensure proper function and for a long, trouble-free life.
© ISO 2021 – All rights reserved v

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INTERNATIONAL STANDARD ISO 4406:2021(E)
Hydraulic fluid power — Fluids — Method for coding the
level of contamination by solid particles
1 Scope
This document specifies the code to be used in defining the quantity of solid particles in the fluid used
in a given hydraulic fluid power system.
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 4407, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the counting method using an optical microscope
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 21018-3, Hydraulic fluid power — Monitoring the level of particulate contamination of the fluid —
Part 3: Use of the filter blockage technique
ISO 21018-4, Hydraulic fluid power — Monitoring the level of particulate contamination in the fluid —
Part 4: Use of the light extinction technique
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Code definitions
4.1 General
The purpose of this code is to simplify the reporting of particle count data by converting the numbers of
particles into broad c
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 4406
ISO/TC 131/SC 6
Hydraulic fluid power — Fluids
Secretariat: BSI
— Method for coding the level of
Voting begins on:
2020­10­08 contamination by solid particles
Voting terminates on:
Transmissions hydrauliques — Fluides — Méthode de codification du
2020­12­03
niveau de pollution particulaire solide
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 4406:2020(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 2020

---------------------- Page: 1 ----------------------
ISO/FDIS 4406:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 4406:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Code definitions. 1
4.1 General . 1
4.2 Basis of code . 2
4.3 Allocation of scale numbers . 2
4.4 Determination of code using automatic particle counter analysis . 3
4.5 Determination of code using microscope sizing . 4
5 Identification statement (reference to this document) . 4
Annex A (normative) Graphical presentation of the code number . 5
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 4406:2020(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 fourth edition cancels and replaces the third edition (ISO 4406:2017), which has been technically
revised.
The main change compared to the previous edition is as follows:
— the use of Particle Contamination Monitors (PCMs) can also be utilized for the determination of the
ISO 4406 contamination code (see subclause 4.4.1) and PCM is referenced throughout this document.
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 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 4406:2020(E)

Introduction
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure
within an enclosed circuit. Solid particle contaminant is always present in the hydraulic fluid and the
amount needs to be determined because the contaminant may cause serious problems.
The ISO 4406 cleanliness code has gained world­wide acceptance as a means of communicating the
cleanliness of a hydraulic fluid. Most hydraulic component manufacturers require a certain ISO
cleanliness level for warranty purposes, to ensure proper function and for a long, trouble-free life.
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 4406:2020(E)
Hydraulic fluid power — Fluids — Method for coding the
level of contamination by solid particles
1 Scope
This document specifies the code to be used in defining the quantity of solid particles in the fluid used
in a given hydraulic fluid power system.
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 4407, Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by
the counting method using an optical microscope
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 21018­3, Hydraulic fluid power — Monitoring the level of particulate contamination of the fluid —
Part 3: Use of the filter blockage technique
ISO 21018­4, Hydraulic fluid power — Monitoring the level of particulate contamination in the fluid —
Part 4: Use of the light extinction technique
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO
...