ISO 8426-1:2025
(Main)Hydraulic fluid power — Determination of derived displacement of positive displacement pumps and motors — Part 1: Two-step Toet method
Hydraulic fluid power — Determination of derived displacement of positive displacement pumps and motors — Part 1: Two-step Toet method
This document specifies the two-step Toet method for the determination of the derived displacement of hydraulic fluid power positive displacement pumps and motors under steady-state conditions. A value for the derived displacement is determined from measurements at multiple shaft speeds.
Transmissions hydrauliques — Détermination de la cylindrée calculée des pompes et moteurs volumétriques — Partie 1: Méthode Toet à deux étapes
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Buy Standard
Standards Content (Sample)
International
Standard
ISO 8426-1
First edition
Hydraulic fluid power —
2025-08
Determination of derived
displacement of positive
displacement pumps and motors —
Part 1:
Two-step Toet method
Transmissions hydrauliques — Détermination de la cylindrée
calculée des pompes et moteurs volumétriques —
Partie 1: Méthode Toet à deux étapes
Reference number
© ISO 2025
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
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units. 1
5 Test procedure . 2
5.1 General requirements .2
5.2 Number of steady-state shaft speeds and differential pressures .3
5.3 Variable displacement unit .3
5.4 Reverse flow unit .3
5.5 Unit used as pump or motor .3
6 Calculation of derived displacement . 4
6.1 General .4
6.2 The two-step Toet method .4
7 Test report . 5
Annex A (informative) Test report examples . 7
Annex B (informative) Formulae for fitting a line .15
Bibliography .16
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
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).
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
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 8,
Product testing.
A list of all parts in the ISO 8426 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 and controlled through a liquid under pressure
within an enclosed circuit. Two types of components of such systems are the positive displacement pumps
and motors. One of the technical parameters of these components is the derived displacement, also known
as derived capacity. The term "derived displacement" is preferred over "derived capacity". This document
describes the test procedure and analytical approach of the two-step Toet method for the determination of
the derived displacement of hydraulic fluid power positive displacement pumps and motors.
v
International Standard ISO 8426-1:2025(en)
Hydraulic fluid power — Determination of derived
displacement of positive displacement pumps and motors —
Part 1:
Two-step Toet method
1 Scope
This document specifies the two-step Toet method for the determination of the derived displacement of
hydraulic fluid power positive displacement pumps and motors under steady-state conditions. A value for
the derived displacement is determined from measurements at multiple shaft speeds.
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 4409:2019, Hydraulic fluid power — Positive-displacement pumps, motors and integral transmissions —
Methods of testing and presenting basic steady state performance
ISO 5598, Fluid power systems and components — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions are given in ISO 5598 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
unit
hydraulic positive displacement pump or motor
4 Symbols and units
The symbols used throughout this document are based on ISO 4391 and shown in Table 1. Graphical symbols
are depicted in accordance with ISO 1219 series.
A diagram showing the use of symbols and graphical symbols is shown in Figure 1.
Table 1 — Symbols, terms and units
Symbol Term Units
α slope of high pressure flow rate vs shaft speed cm /r
i
j number of shaft speeds —
k number of measurement points —
number of differential pressures —
n
shaft speed r/min
a
Δp differential pressure bar (MPa)
a
p rated max pressure bar (MPa)
rated
a
maximum targeted differential pressure bar (MPa)
Δp
maxt, arget
a
minimum targeted differential pressure bar (MPa)
Δp
mint, arget
a
p inlet pressure bar (MPa)
a
target inlet pressure bar (MPa)
p
1,target
a
p outlet pressure bar (MPa)
a
target outlet pressure bar (MPa)
p
2,target
a
case pressure bar (MPa)
p
d
q high pressure flow rate l/min
ve
inlet temperature °C
θ
V derived displacement cm /r
i
a 5 2
1 bar = 10 Pa = 0,1 MPa; 1 Pa = 1 N/m .
a) Pump b) Motor
Figure 1 — Example use of symbols, subscripts and graphical symbols for pumps and motors
5 Test procedure
5.1 General requirements
Measurements for positive displacement pumps shall be carried out in accordance with ISO 4409:2019, 5.1
and 5.2.
Measurements for positive displacement motors shall be carried out in accordance with ISO 4409:2019, 5.1
and 5.3.
Suspect values shall be re-evaluated at the appropriate conditions to determine if the data were in error or
an anomaly in expected performance exists at these specified test conditions.
5.2 Number of steady-state shaft speeds and differential pressures
Five or more shaft speeds and five or more differential pressures shall be used. This implies 25 or more
measurement points shall be used.
The maximum targeted differential pressure, Δp , of the test is defined as follows:
maxt, arget
— If p ≤50 bar ,
rated
— for a pump use Δpp=− p ;
maxt,,argetrated 1 target
— for a motor use Δpp=− p .
maxt,,argetrated 2 target
— If p >50 bar ,
rated
p −50
rated
— for a pump use Δp = +−50 p ;
maxt,,arget 1 target
p −50
rated
— for a motor use Δp = +−50 p .
maxt,,arget 2 target
The differential pressure shall be increased in approximately equal increments from minimum targeted
differential pressure, Δp , to maximum targeted differential pressure, Δp , of the unit to
mint, arget maxt, arget
avoid clustering some of the points around one target value. A tolerance of ±5 % of Δp for the
maxt, arget
targeted differential pressures shall be met.
The shaft speed shall be increased in approximately equal increments from minimum targeted shaft speed
for constant rotation (not zero rev/min) to maximum rated shaft speed of the unit to avoid clustering some
of the points around one value. A tolerance of ±5 % of the maximum rated shaft speed for the targeted shaft
speeds shall be met.
5.3 Variable displacement unit
The data for performing the estimation of the derived displacement of variable displacement pump or motor
shall be obtained following ISO 4409:2019, 5.2.4 (pump) and respectively 5.3.4 (motor).
5.4 Reverse flow unit
If the unit can be operated in both flow directions and the derived displacement depends on the flow
direction, the derived displacement shall be determined for each.
5.5 Unit used as pump or motor
A unit intended to be used as pump shall be tested as pump and a unit intended to be used as motor shall be
tested as motor. The derived displacement determined when a given unit is tested as a pump can differ from
that determined when the unit is tested as a motor. If both operation modes are considered necessary, the
test shall be carried out for both operation modes.
6 Calculation of derived displacement
6.1 General
The mathematical definition of the derived displacement is shown in Formula 1. Expressing Formula 1 in
words, the derived displacement is the slope of the high pressure flow rate with respect to shaft speed
evaluated at zero differential pressure. One of the fundamental implications of the two-step Toet method is
derived displacement is assumed to be independent of speed and differential pressure according to Clause 4
of Reference [3] and Clause 4 of Reference. [4] Therefore, the task of finding the derived displacement is to
find the slope of the high pressure flow rate with respect to shaft speed at zero differen
...
FINAL DRAFT
International
Standard
ISO/FDIS 8426-1
ISO/TC 131/SC 8
Hydraulic fluid power —
Secretariat: BSI
Determination of derived
Voting begins on:
displacement of positive
2025-05-26
displacement pumps and motors —
Voting terminates on:
2025-07-21
Part 1:
Two-step Toet method
Transmissions hydrauliques — Détermination de la cylindrée
calculée des pompes et moteurs volumétriques —
Partie 1: Méthode Toet à deux étapes
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
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
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.
Reference number
ISO/FDIS 8426-1:2025(en) © ISO 2025
FINAL DRAFT
ISO/FDIS 8426-1:2025(en)
International
Standard
ISO/FDIS 8426-1
ISO/TC 131/SC 8
Hydraulic fluid power —
Secretariat: BSI
Determination of derived
Voting begins on:
displacement of positive
displacement pumps and motors —
Voting terminates on:
Part 1:
Two-step Toet method
Transmissions hydrauliques — Détermination de la cylindrée
calculée des pompes et moteurs volumétriques —
Partie 1: Méthode Toet à deux étapes
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.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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 Reference number
ISO/FDIS 8426-1:2025(en) © ISO 2025
ii
ISO/FDIS 8426-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units. 1
5 Test procedure . 2
5.1 General requirements .2
5.2 Number of steady-state shaft speeds and differential pressures .3
5.3 Variable displacement unit .3
5.4 Reverse flow unit .3
5.5 Unit used as pump or motor .3
6 Calculation of derived displacement . 4
6.1 General .4
6.2 The two-step Toet method .4
7 Test report . 5
Annex A (informative) Test report examples . 7
Annex B (informative) Formulae for fitting a line .15
Bibliography . 17
iii
ISO/FDIS 8426-1:2025(en)
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).
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
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 8,
Product testing.
A list of all parts in the ISO 8426 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
ISO/FDIS 8426-1:2025(en)
Introduction
In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure
within an enclosed circuit. Two types of components of such systems are the positive displacement pumps
and motors. One of the technical parameters of these components is the derived displacement, also known
as derived capacity. This document is intended to describe the test procedure and analytical approach
of the two-step Toet method for determining the derived displacement of hydraulic fluid power positive
displacement pumps and motors. The term derived displacement is preferred over derived capacity.
v
FINAL DRAFT International Standard ISO/FDIS 8426-1:2025(en)
Hydraulic fluid power — Determination of derived
displacement of positive displacement pumps and motors —
Part 1:
Two-step Toet method
1 Scope
This document specifies the two-step Toet method for the determination of the derived displacement of
hydraulic fluid power positive displacement pumps and motors under steady-state conditions. A value for
the derived displacement is determined from measurements at multiple shaft speeds.
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 4409:2019, Hydraulic fluid power — Positive-displacement pumps, motors and integral transmissions —
Methods of testing and presenting basic steady state performance
ISO 5598, Fluid power systems and components — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions are given in ISO 5598 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
unit
hydraulic positive displacement pump or motor
4 Symbols and units
The symbols used throughout this document are based on ISO 4391 and shown in Table 1. Graphical symbols
are depicted in accordance with ISO 1219 series.
A diagram showing the use of symbols and graphical symbols is shown in Figure 1.
ISO/FDIS 8426-1:2025(en)
Table 1 — Symbols, terms and units
Symbol Term Units
α slope of high pressure flow rate vs shaft speed cm /r
i
j number of shaft speeds —
k number of measurement points —
number of differential pressures —
n
shaft speed r/min
a
Δp differential pressure bar (MPa)
a
p rated max pressure bar (MPa)
rated
a
maximum targeted differential pressure bar (MPa)
Δp
maxt, arget
a
minimum targeted differential pressure bar (MPa)
Δp
mint, arget
a
p inlet pressure bar (MPa)
a
target inlet pressure bar (MPa)
p
1,target
a
p outlet pressure bar (MPa)
a
target outlet pressure bar (MPa)
p
2,target
a
case pressure bar (MPa)
p
d
q high pressure flow rate l/min
ve
inlet temperature °C
θ
V derived displacement cm /r
i
a 5 2
1 bar = 10 Pa = 0,1 MPa; 1 Pa = 1 N/m .
a) Pump b) Motor
Figure 1 — Example use of symbols, subscripts and graphical symbols for pumps and motors
5 Test procedure
5.1 General requirements
Measurements for positive displacement pumps shall be carried out in accordance with ISO 4409:2019, 5.1
and 5.2.
ISO/FDIS 8426-1:2025(en)
Measurements for positive displacement motors shall be carried out in accordance with ISO 4409:2019, 5.1
and 5.3.
Suspect values shall be re-evaluated at the appropriate conditions to determine if the data were in error or
an anomaly in expected performance exists at these specified test conditions.
5.2 Number of steady-state shaft speeds and differential pressures
Five or more shaft speeds and five or more differential pressures shall be used. This implies 25 or more
measurement points shall be used.
The maximum targeted differential pressure, Δp , of the test is defined as follows:
maxt, arget
— If p ≤50 bar ,
rated
— for a pump use Δpp=− p ;
maxt,,argetrated 1 target
— for a motor use Δpp=− p .
maxt,,argetrated 2 target
— If p >50 bar ,
rated
p −50
rated
— for a pump use Δp = +−50 p ;
maxt,,arget 1 target
p −50
rated
— for a motor use Δp = +−50 p .
maxt,,arget 2 target
The differential pressure shall be increased in approximately equal increments from minimum targeted
differential pressure, Δp , to maximum targeted differential pressure, Δp , of the unit to
mint, arget maxt, arget
avoid clustering some of the points around one target value. A tolerance of ±5 % of Δp for the
maxt, arget
targeted differential pressures shall be met.
The shaft speed shall be increased in approximately equal increments from minimum targeted shaft speed
for constant rotation (not zero rev/min) to maximum rated shaft speed of the unit to avoid clustering some
of the points around one value. A tolerance of ±5 % of the maximum rated shaft speed for the targeted shaft
speeds shall be met.
5.3 Variable displacement unit
The data for
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ISO/FDIS 8426-1:2025(en)
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ISO /TC 131/SC 08/WG 13 8
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Secretariat: BSI .
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Date: 2025-04-23xx
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Hydraulic fluid power - — Determination of derived displacement of
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Part 1:
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Two-step Toet method
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Transmissions hydrauliques — Détermination de la cylindrée calculée des pompes et moteurs volumétriques —
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Partie 1: Méthode Toet à deux étapes
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ISO/FDIS 8426-1:2025(en)
Formatted: Font: Bold
Formatted: HeaderCentered
Commented [eXtyles1]: The reference "ISO 2025" is to a
withdrawn standard
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
Formatted: Default Paragraph Font
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 Formatted: Default Paragraph Font
at the address below or ISO’s member body in the country of the requester.
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Formatted: French (France)
EmailE-mail: copyright@iso.org
Formatted: French (France)
Website: www.iso.orgwww.iso.org
Formatted: French (France)
Published in Switzerland
Formatted: FooterPageRomanNumber, Space After: 0
pt
ii
ISO/FDIS 8426-1:2025(en)
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Contents
Formatted: None, Adjust space between Latin and
Asian text, Adjust space between Asian text and
Foreword . v
numbers
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 1
5 Test procedure . 3
5.1 General requirements . 3
5.2 Number of steady-state shaft speeds and differential pressures . 3
5.3 Variable displacement unit . 4
5.4 Reverse flow unit . 4
5.5 Unit used as pump or motor . 4
6 Calculation of derived displacement . 4
6.1 General. 4
6.2 The two-step Toet method . 4
7 Test report . 7
Annex A (informative) Test report examples . 9
Annex B (informative) Formulae for fitting a line . 19
Bibliography . 21
Contents . iii
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 2
5 Test procedure . 3
5.1 General requirements . 3
5.2 Number of steady-state shaft speeds and differential pressures . 3
5.3 Variable displacement unit . 3
5.4 Reverse flow unit . 3
5.5 Unit used as pump or motor . 3
6 Calculation of derived displacement . 4
6.1 General. 4
Formatted: Font: 10 pt
6.2 The two-step Toet method . 4
Formatted: Font: 10 pt
7 Test Report . 5
Formatted: Font: 10 pt
Annex A (informative) Test report examples . 7
Formatted: FooterCentered, Left, Space Before: 0 pt,
A.1 Pump test report example . 7 Line spacing: single
Formatted: FooterPageRomanNumber, Left, Space
A.1.1 Raw Data . 7
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© ISO 2025 – All rights reserved
iii
ISO/FDIS 8426-1:2025(en)
Formatted: Font: Bold
Formatted: HeaderCentered
A.1.2 Example report . 8
A.1.3 Two-step Toet method results . 8
A.2 Motor test report example. 10
A.2.1 Raw data . 10
A.2.2 Example report . 11
A.2.3 Two-step Toet method results . 12
Annex B (informative) Formulae for fitting a line . 14
Bibliography . 15
Formatted: FooterPageRomanNumber, Space After: 0
pt
iv
ISO/FDIS 8426-1:2025(en)
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Foreword
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
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/directiveswww.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 this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
Commented [eXtyles2]: The URL
https://www.iso.org/patents has been redirected to
patent rights.
http://www.iso.org/iso-standards-and-patents.html. Please
verify the URL.
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.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 8,
Product testing.
A list of all parts in the ISO 8426 series can be found on the ISO website.
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Any feedback or questions on this document should be directed to the user’s national standards body. A
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complete listing of these bodies can be found at www.iso.org/members.html.www.iso.org/members.html.
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