ISO 23551-1:2024

International
Standard
ISO 23551-1
Third edition
Safety and control devices for
2024-11
gas burners and gas-burning
appliances — Particular
requirements —
Part 1:
Automatic and semi-automatic shut-
off valves
Dispositifs de commande et de sécurité pour brûleurs à gaz et
appareils à gaz — Exigences particulières —
Partie 1: Robinets automatiques et semi-automatiques
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .vi
Introduction .viii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to valves .2
3.2 General terms .3
4 Classification . 5
4.1 Classes of control .5
4.1.1 Classification based on sealing force .5
4.1.2 Classification based on pressure surge.5
4.1.3 Classification with neither sealing force nor pressure surge .5
4.1.4 Classification of flow control valves for general purpose .5
4.2 Groups of controls .6
4.3 Types of DC supplied controls .6
4.4 Classes of control functions .6
5 Test conditions and tolerances . 6
6 Construction . 6
6.1 General .6
6.2 Construction requirements.8
6.2.1 Appearance .8
6.2.2 Holes .8
6.2.3 Breather holes .8
6.2.4 Vent limiter .8
6.2.5 Screwed fastenings .8
6.2.6 Moving parts .8
6.2.7 Sealing caps .8
6.2.8 Disassembling and assembling for servicing and/or adjustment for controls .8
6.2.9 Auxiliary channels and orifices .10
6.2.10 Pre-setting device .10
6.2.11 Closed position indication .10
6.2.12 Specific construction .11
6.2.13 Flow rates of valves with modulating control .11
6.2.14 Bypass . 12
6.2.15 Semi-automatic shut-off valve . 12
6.2.16 Diaphragm type valve . 12
6.2.17 Balanced valves with one or two ports . 12
6.3 Materials .14
6.3.1 General material requirements .14
6.3.2 Housing .14
6.3.3 Springs providing closing force and sealing force .14
6.3.4 Resistance to corrosion and surface protection .14
6.3.5 Impregnation .14
6.3.6 Seals for glands for moving parts. 15
6.3.7 Jointing . 15
6.3.8 Closure members . 15
6.4 Connections . 15
6.4.1 General . 15
6.4.2 Connection sizes . 15
6.4.3 Connections types . 15
6.4.4 Threads . 15
6.4.5 Union joints . 15
6.4.6 Flanges . 15

iii
6.4.7 Compression fittings . 15
6.4.8 Flare connections .16
6.4.9 Nipples for pressure tests .16
6.4.10 Strainers . . .16
6.4.11 Gas connections by GQC .16
6.4.12 Hydraulic and pneumatic actuating mechanisms .16
6.5 Gas controls employing electrical components in the gas way .16
7 Performance .16
7.1 General .16
7.2 Leak-tightness .18
7.2.1 General .18
7.2.2 Requirements .18
7.2.3 Test . . .18
7.2.4 Pressure surge test .18
7.3 Torsion and bending .18
7.4 Rated flow rate .18
7.4.1 General .18
7.4.2 Requirements .18
7.4.3 Test . . .18
7.5 Durability .19
7.6 Functional requirements . .19
7.6.1 Closing function .19
7.6.2 Opening and closing function of thermoelectric valves . 20
7.6.3 Closing force . 20
7.6.4 Delay time and opening time . 20
7.6.5 Closing time .21
7.6.6 Sealing force . 22
7.6.7 Gas cracking. 23
7.7 Endurance . 23
7.7.1 Requirements . 23
7.7.2 Test . . . 25
7.8 Hydrostatic withstand pressure test .27
7.8.1 General .27
7.8.2 Requirements .27
7.8.3 Test . . .27
7.9 Resistance to permanent damage at excessive supply pressure . 28
7.9.1 General . 28
7.9.2 Requirement . 28
7.9.3 Test . . . 28
8 Electrical equipment .28
8.1 General . 28
8.2 Requirements . 28
8.3 Test . 28
8.4 Protection by enclosure . 28
8.5 Electrical components . 29
8.5.1 Switches . 29
8.5.2 Plug connector . 29
8.5.3 Power-saving circuit . 29
9 Electromagnetic compatibility (EMC) . .30
9.1 Protection against environmental influences . 30
9.1.1 General . 30
9.1.2 Requirements . 30
9.2 Harmonics and interharmonics including mains signalling at a. c. power port, low
frequency immunity . 30
9.3 Voltage dips, voltage interruptions and voltage variations in the power supply network . 30
9.4 Test of influence of voltage unbalance . 30
9.5 Surge immunity test . 30

iv
9.6 Electrical fast transient/burst . 30
9.7 Ring wave immunity .31
9.8 Electrostatic discharge .31
9.9 Radio-frequency electromagnetic field immunity .31
9.10 Influence of supply frequency variations .31
9.11 Power frequency magnetic field immunity .31
9.12 Evaluation of compliance .31
10 Marking, installation and operating instructions .31
10.1 Marking .31
10.2 Installation and operating instructions .32
10.3 Warning notice .32
10.4 Annexes .32
Annex A (normative) Specific regional requirements in Canada and the USA .33
Annex B (normative) Specific regional requirements in Japan .34
Bibliography .35

v
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 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
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 161, Controls and protective devices for gaseous
and liquid fuels.
This third edition cancels and replaces the second edition (ISO 23551-1:2012), which has been technically
revised.
The main changes are as follows:
— definitions for specific valve types have been updated and a flow chart for valve types has been added
(Clause 3, Table 1);
— the classification of the valve types has been restructured, including the addition of a new classification
Class E and the definition of valves without safety shut-off function as general purpose valve Class D
(Clause 4);
— common requirements and tests for specific valve types have been summarized in tabular form (see
Tables 1 and 2);
— visual indicator (VI), closed position switch (CPS) and proof of closure switch (POC) have been
summarized in 6.2.11;
— the endurance test has been restructured, with the assignment of the test cycles and tests summarized
in tabular form (see Tables 4, 5 and 6);
— a hydrostatic withstand pressure test has been added;
— a resistance to permanent damage at excessive supply pressure test has been added;
— the document has been updated to align technically and with the revised format of the latest edition of
ISO 23550;
— specific regional requirements that were previously contained in regional Annexes have been moved
into the main body of the text;

vi
— the document has been updated to align with the application of Electromagnetic compatibility (EMC)
testing from IEC 60730-2-17 (withdrawn 2017-02-20 and replaced by ISO 23551-1);
— the document has been updated and aligned with IEC 60730-1:2022.
A list of all parts in the ISO 23551 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.

vii
Introduction
This document is designed to be used in combination with ISO 23550. Together, they establish the full
requirements as they apply to the product covered by this document.
Where needed, this document adapts ISO 23550 by stating in the corresponding clause:
— “with the following modification”;
— “with the following addition”;
— “is replaced by the following”; or
— “is not applicable”.
In order to identify specific requirements that are particular to this document and that are not already
covered by ISO 23550, this document contains certain clauses or subclauses that are additional to the
structure of ISO 23550. These subclauses are indicated by the introductory sentence: “Subclause (or Annex)
specific to this document.”
To ensure global relevance of this document, the differing requirements resulting from practical experience
and installation practices in various regions of the world have been taken into account. The variations in
basic infrastructure associated with gas controls and appliances have also been recognized, some of which
are addressed in Annexes A and B. This document intends to provide a basic framework of requirements
that recognize these differences.

viii
International Standard ISO 23551-1:2024(en)
Safety and control devices for gas burners and gas-burning
appliances — Particular requirements —
Part 1:
Automatic and semi-automatic shut-off valves
1 Scope
This document specifies safety, constructional and performance requirements and testing of automatic,
semi-automatic shut-off valves and general purpose valves for gas burners, gas appliances and appliances of
similar use, hereinafter referred to as valves.
This document applies to normally closed valves and general purpose valves mounted upstream to gas
burners and gas appliances with declared maximum operating pressures up to and including 500 kPa, for use
on burners or in appliances using fuel gases such as natural gas, manufactured gas or liquefied petroleum
gas (LPG). It is not applicable to corrosive and waste gases.
This document applies to:
— valves directly or indirectly actuated, electrically or by mechanical means;
— valves actuated by hydraulic or pneumatic means;
— valves where the flow rate is controlled by external electrical signals, either in discrete steps or
proportional to the applied signal; and
— valves fitted with closed position indicator switches.
This document covers type testing only.
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 23550:2018, Safety and control devices for gas and/or oil burners and appliances — General requirements
IEC 60529, Degrees of protection provided by enclosures (IP-code)
IEC 60730-1:2022, Automatic electrical controls— Part 1: General requirements
IEC 61058-1, Switches for appliances — Part 1: General requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 23550 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 Terms related to valves
3.1.1
valve
device consisting essentially of a valve body, closure member and valve actuator (3.2.18) that controls the
flow of gas
Note 1 to entry: The valve actuation can be achieved by gas pressure, electrical, hydraulic, manual or pneumatic energy.
Note 2 to entry: See Figure 1.
Figure 1 — Valve type flow chart
3.1.2
semi-automatic shut-off valve
valve (3.1.1) that is opened manually and closes automatically upon removal of the actuating energy (3.2.2)
Note 1 to entry: See Figure 1.
3.1.3
automatic shut-off valve
valve (3.1.1) which opens when energized and closes automatically when de-energized
Note 1 to entry: See Figure 1.
3.1.4
C/I valve
commercial/industrial valve
normally closed automatic or semi-automatic shut-off valve (3.1.3; 3.1.2) having an operating pressure of
3,5 kPa or greater
Note 1 to entry: See Figure 1.
3.1.5
general purpose valve
valve (3.1.1) intended to control the flow of gas that does not provide a shut-off function
Note 1 to entry: A combination of a general purpose valve and a shut-off valve is primarily considered as a shut-off valve.
Note 2 to entry: See Figure 1.

3.1.6
thermoelectric valve
semi-automatic shut-off valve (3.1.2) that receives its electrical actuating energy by means of a
thermoelectric source
Note 1 to entry: Not applicable for C/I valves (3.1.4).
Note 2 to entry: See Figure 1.
3.1.7
diaphragm type valve
automatic shut-off valve (3.1.3) where a closing member is opened by application of gas pressure upon a
flexible diaphragm
Note 1 to entry: See Figure 1.
3.1.8
valve with step control
multi-stage valve
valve (3.1.1) which controls the flow rate in steps
Note 1 to entry: See Figure 1.
3.1.9
valve with modulating control
modulating valve
valve (3.1.1) which controls the flow rate continuously between two limits in response to external signals
Note 1 to entry: See Figure 1.
3.2 General terms
3.2.1
actuating mechanism
part of the valve (3.1.1) which moves the closure member to the open position
3.2.2
actuating energy
required energy for the actuating mechanism (3.2.1) to move the closure member to the open position
Note 1 to entry: The actuating energy may have an external source (electrical, hydraulic or pneumatic) and can be
transformed inside the valve (3.1.1).
3.2.3
closing force
force available to close the valve (3.1.1), independent of any force provided by gas pressure
3.2.4
sealing force
force acting on the valve (3.1.1) seat when the closure member is in the closed position, independent of any
force provided by gas pressure
3.2.5
frictional force
largest force required to move the actuating mechanism (3.2.1) and the closure member from the open
position to the closed position with the closure spring removed, independent of any force provided by gas
pressure
3.2.6
actuating pressure
hydraulic or pneumatic pressure supplied to the actuating mechanism (3.2.1) of the valve (3.1.1)

3.2.7
opening time
time interval between energizing the valve (3.1.1) and the attainment of the maximum or other defined flow rate
3.2.8
closing time
time interval between de-energizing the valve (3.1.1) and the closure member attaining the closed position
3.2.9
delay time
time interval between energizing the valve (3.1.1) and the start of flow
3.2.10
control valve
valve (3.1.1) which controls the hydraulic or pneumatic means supplied to the actuating mechanism (3.2.1)
3.2.11
rated voltage
voltage declared by the manufacturer at which the valve (3.1.1) may be operated
3.2.12
rated current
current declared by the manufacturer at which the valve (3.1.1) may be operated
3.2.13
bypass
passage, provided in the body of the device or in a gas line around the body, which permits a gas flow from
the inlet to the outlet connections of the device entirely independent of the action of the valve (3.1.1)
3.2.14
interlock
control or device to prove the physical state of a required condition, and to furnish proof to the automatic
gas ignition system or other safety control circuit
3.2.15
proof of closure switch
POC
electrical switch which monitors the closed position of the valve (3.1.1) closure member, and which is used
as an interlock (3.2.14)
3.2.16
closed position switch
CPS
switch fitted to a valve (3.1.1) which indicates when the closure member is in the closed position, and which
is used as an interlock (3.2.14)
Note 1 to entry: For certain applications, a CPS is also known as a closed position indicator (CPI) switch.
3.2.17
switching element
electrical switch actuated by the valve actuator (3.2.18) and used as an electrical output
3.2.18
valve actuator
electrically operated mechanism (for example an electric motor or stepping solenoid), an electro-thermal
device (for example the heating element of an energy regulator) or a mechanical device, used to effect the
operation of a valve (3.1.1)
3.2.19
balanced valve with two ports
valve (3.1.1) with a balanced closure member, two valve discs and two valve seats where the inlet pressure
acts on the closure member in the closing direction
Note 1 to entry: Examples are shown in Figure 2.
3.2.20
balanced valve with one port
valve (3.1.1) with a balanced closure member, one valve disc and balancing means where the inlet pressure
acts on the closure member in the closing direction
Note 1 to entry: An example is shown in Figure 3.
3.2.21
hydrostatic withstand pressure
pressure resistance
pressure which acts on the pressure carrying parts of a valve (3.1.1) under an abnormal overpressure
condition
Note 1 to entry: Functional properties are not considered.
4 Classification
4.1 Classes of control
Shall be according to ISO 23550:2018, 4.1 with the following addition:
4.1.1 Classification based on sealing force
Subclause specific to this document.
Automatic shut-off valves where the sealing force is not decreased by the gas inlet pressure are classified
according to sealing force requirements and shall be designated according to Class A, B, C or J (see Tables 1,
2, 4 and 6).
These valves may also have:
— modulating control function, or
— step control function/multi-stage.
4.1.2 Classification based on pressure surge
Subclause specific to this document.
Automatic and semi-automatic shut-off valves with pressure surge requirements shall be designated
according to Class C/I (see 3.1.4 and Tables 1, 2, 4 and 6).
4.1.3 Classification with neither sealing force nor pressure surge
Subclause specific to this document.
Automatic and semi-automatic shut-off valves without sealing force and without pressure surge
requirements shall be designated according to Class E (see Tables 1, 2, 4 and 6).
4.1.4 Classification of flow control valves for general purpose
Subclause specific to this document.

General purpose valves with modulating control that do not provide a shut-off function shall be designated
according to Class D (see Tables 1, 2, 4 and 6).
These valves include:
— valves with modulating control function;
— valves with step control function/multi-stage.
4.2 Groups of controls
Shall be according to ISO 23550:2018, 4.2.
4.3 Types of DC supplied controls
Shall be according to ISO 23550:2018, 4.3.
4.4 Classes of control functions
Shall be according to ISO 23550:2018, 4.4.
5 Test conditions and tolerances
Shall be according to ISO 23550:2018, Clause 5.
6 Construction
6.1 General
Shall be according to ISO 23550:2018, 6.1 with the following modification.
Table 1 describes the applicable construction requirements and tests for the classified valves. Combinations
of valve types are not excluded (e.g. automatic Class A and automatic C/I). If the respective construction
requirement is used, the design shall be according to the assigned clause in Table 1, if applicable.
The marking "x” identifies the minimum requirements to be verified by the given subclauses in this
document.
Requirements without existing construction or performance properties cannot be verified and such
associated clauses are therefore not applicable.
EXAMPLE Strainers are an optional element in the design of the valve. Therefore, 6.4.10 is not always applicable,
even though the assignment is given in Table 1.

Table 1 — Assignment of valve construction requirements and tests
Clause Title Shut-off valve (Classes) General
purpose
automatic auto- semi-au- auto- semi-au-
valve
matic tomatic matic tomatic
(Class)
A B C J C/I C/I E E D
6.2 Construction requirements
6.2.1 Appearance x x x x x x x x x
6.2.2 Holes x x x x x x x x x
6.2.3 Breather holes x x x x x x x x x
6.2.4 Vent limiter x x x x x x x x x
6.2.5 Screwed fastenings x x x x x x x x x
6.2.6 Moving parts x x x x x x x x x
6.2.7 Sealing caps x x x x x x x x x
6.2.8 Disassembling and assembling x x x x x x x x x
for servicing and/or adjustment
for controls
6.2.9 Auxiliary channels and orifices x x x x x x x x x
6.2.10 Pre-setting device x x x x x x x x x
6.2.11 Closed position indication x x x x x x x x —
6.2.12 Specific construction x x x — x x — — —
6.2.13 Flow rates of valves with modu- x x x x x x x x x
lating control
6.2.14 Bypass x x x x x x x x —
6.2.15 Semi-automatic shut-off valve — — — — — x — x —
6.2.16 Diaphragm type valve x x x x x x x x x
6.2.17 Balanced valves with one or two x — — — — — x x x
ports
6.3 Materials x x x x x x x x x
6.4 Connections — — — — — — — — —
6.4.1 General x x x x x x x x x
6.4.2 Connection sizes x x x x x x x x x
6.4.3 Connection types x x x x x x x x x
6.4.4 Threads x x x x x x x x x
6.4.5 Union joints x x x x x x x x x
6.4.6 Flanges x x x x x x x x x
6.4.7 Compression fittings x x x x x x x x x
6.4.8 Flare connections x x x x x x x x x
6.4.9 Nipples for pressure tests x x x x x x x x x
6.4.10 Strainers x x x x x x x x x
6.4.11 Gas connections by GQC x x x x x x x x x
6.4.12 Hydraulic and pneumatic x x x x x x x x x
actuating mechanisms
6.5 Gas controls employing x x x x x x x x x
electrical components in the gas
way
Key
x  required only if the construction is present in the design of the valve
—  no requirement even if the function is present
GQC  gas quick connector
6.2 Construction requirements
6.2.1 Appearance
Shall be according to ISO 235
...