ISO 23550:2018

INTERNATIONAL ISO
STANDARD 23550
Third edition
2018-04
Safety and control devices for gas
and/or oil burners and appliances —
General requirements
Dispositifs de commande et de sécurité pour brûleurs à gaz et
appareils à gaz — Exigences générales
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classification . 5
4.1 Classes of control . 5
4.2 Groups of controls . 5
4.3 Types of DC supplied controls . 5
4.4 Classes of control functions . 5
5 Test conditions and tolerances . 6
5.1 Test conditions . 6
5.2 Tolerances . 6
6 Construction . 7
6.1 General . 7
6.2 Construction requirements . 7
6.2.1 Appearance . 7
6.2.2 Holes . 7
6.2.3 Breather holes . 8
6.2.4 Vent limiter . 8
6.2.5 Screwed fastenings . 9
6.2.6 Moving parts . 9
6.2.7 Sealing caps . 9
6.2.8 Disassembling and assembling for servicing and/or adjustment for controls .10
6.2.9 Auxiliary channels and orifices .10
6.2.10 Pre-setting device .10
6.3 Materials .11
6.3.1 General material requirements .11
6.3.2 Housing .11
6.3.3 Springs providing closing force and sealing force .12
6.3.4 Resistance to corrosion and surface protection .12
6.3.5 Impregnation .12
6.3.6 Seals for glands for moving parts .13
6.3.7 Jointing .13
6.4 Connections .13
6.4.1 General.13
6.4.2 Connection sizes .13
6.4.3 Connection types .14
6.4.4 Threads .15
6.4.5 Union joints .16
6.4.6 Flanges .16
6.4.7 Compression fittings . . .16
6.4.8 Flare connections .17
6.4.9 Nipples for pressure tests .17
6.4.10 Strainers .17
6.4.11 Gas connections by GQC .18
6.5 Gas controls employing with electrical components in the gas way .18
6.5.1 General.18
6.5.2 Requirements .18
6.5.3 Ignition trial test .18
6.5.4 Test of ignition source .19
7 Performance .20
7.1 General .20
7.2 Leak-tightness.21
7.2.1 General.21
7.2.2 Requirements .21
7.2.3 Test .21
7.3 Torsion and bending .24
7.3.1 General.24
7.3.2 Torsion .24
7.3.3 Bending moment .24
7.3.4 Torsion and bending tests .24
7.4 Rated flow rate .28
7.4.1 General.28
7.4.2 Requirements .28
7.4.3 Test .28
7.5 Durability .30
7.5.1 Elastomers in contact with gas .30
7.5.2 Resistance of elastomers to lubricants and gases .30
7.5.3 Marking resistance .31
7.5.4 Resistance to scratching .31
7.5.5 Resistance to humidity .32
7.6 Functional requirements .33
7.7 Endurance .33
7.8 Vibration test .33
8 Electrical equipment .33
8.1 General .33
8.2 Requirements .33
8.3 Test .34
8.4 Protection by enclosure.34
9 Electromagnetic compatibility (EMC) .34
9.1 Protection against environmental influences .34
9.1.1 General.34
9.1.2 Requirements .34
9.1.3 Test .35
9.2 Harmonics and interharmonics including mains signalling at a.c. power port, low
frequency immunity .35
9.2.1 General.35
9.2.2 Requirements .35
9.2.3 Test .35
9.3 Voltage dips, voltage interruptions and voltage variations in the power supply network 35
9.3.1 Voltage dips and voltage interruptions .35
9.3.2 Test .35
9.3.3 Voltage variation .36
9.4 Test of influence of voltage unbalance .36
9.5 Surge immunity tests .36
9.5.1 General.36
9.5.2 Requirements .36
9.5.3 Test .37
9.6 Electrical fast transient/burst .37
9.6.1 General.37
9.6.2 Requirements .37
9.6.3 Test .37
9.7 Ring wave immunity .37
9.7.1 General.37
9.7.2 Requirements .37
9.7.3 Test .37
9.8 Electrostatic discharge .37
9.8.1 General.37
iv © ISO 2018 – All rights reserved

9.8.2 Requirements .38
9.8.3 Test .38
9.9 Radio-frequency electromagnetic field immunity .38
9.9.1 Immunity to conducted disturbances .38
9.9.2 Immunity to radiated disturbances .38
9.10 Influence of supply frequency variations .39
9.10.1 General.39
9.10.2 Requirements .39
9.10.3 Test .39
9.11 Power frequency magnetic field immunity .39
9.11.1 General.39
9.11.2 Requirements .39
9.11.3 Test .39
9.12 Evaluation of compliance .39
10 Marking, installation and operating instructions .39
10.1 Marking .39
10.2 Installation and operating instructions .39
10.3 Warning notice .40
Annex A (informative) Leak-tightness test — Volumetric method .41
Annex B (informative) Leak-tightness test — Pressure-loss method .43
Annex C (normative) Conversion of pressure loss into leakage rate .44
Annex D (normative) Gas quick connector (GQC) .45
Annex E (normative) Elastomers/requirements resistance to lubricants and gas .51
Annex F (normative) Specific regional requirements in European countries .59
Annex G (normative) Specific regional requirements in Canada and USA .60
Annex H (normative) Specific regional requirements in Japan .62
Bibliography .65
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 on 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 the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 161, Controls and protective devices for
gas and/or oil.
This third edition cancels and replaces the second edition (ISO 23550:2011), which has been technically
revised. The main changes compared to the previous edition are as follows:
— a new structure has been introduced with a clear separation between general statements,
requirements and test;
— this document has been updated and aligned with the relevant parts of IEC 60730-1:2013;
— the Scope now specifies controls for use at maximum operating pressures up to and including
500 kPa;
— the Introduction and Clauses 2 and 3 have been updated;
— the structure of Clauses 4 to 10 have been modified;
— in Formula (2), the air flow rate at standard conditions has been corrected;
— Annexes D to H have been created;
— the Bibliography has been updated.
vi © ISO 2018 – All rights reserved

Introduction
This document provides general requirements for controls and safety devices for gas burners and gas
burning appliances, and is intended to be used in conjunction with the ISO 23551, ISO 23552 and the
ISO 23553 series for specific types of controls, or for controls for specific applications.
This document can also be applied, so far as reasonable, to controls not mentioned in a specific standard
and to controls designed on new principles, in which case additional requirements can be necessary.
Where no specific International Standard for a control exists, the control can be tested according to
this document and further tests which take into account the intended use.
Controls and safety devices for gas burners and gas burning appliances using fuel need to withstand
the type of gas which is specified. Other ISO Technical Committees, e.g. ISO/TC 28, Petroleum products
and lubricants and ISO/TC 193, Natural gas, deal with the testing and properties of fuel gases.
Note that, due to the differing properties of fuel depending on its source/region of origin, certain
differences in regulations exist at present in different regions, some of which are presented in Annexes F,
G and H. This document intends to provide a basic framework of requirements until these differences
can be harmonized.
INTERNATIONAL STANDARD ISO 23550:2018(E)
Safety and control devices for gas and/or oil burners and
appliances — General requirements
1 Scope
This document specifies safety, construction, performance and testing requirements for controls
for gas burners and gas burning appliances for use with natural gas, manufactured gas or liquefied
petroleum gas (LPG).
This document applies to controls for use at maximum operating pressures up to and including 500 kPa.
This document provides the general requirements that are intended to be the basis for the specific
control standards found in the ISO 23551 and ISO 23552 series. These include the following:
— automatic and semi-automatic gas valves;
— gas thermoelectric flame supervision controls;
— gas and oil /air ratio controls;
— gas pressure regulators;
— manual gas valves;
— mechanical gas thermostats;
— multifunctional gas controls;
— air and gas pressure-sensing devices;
— gas vent valves;
— gas valve-proving systems.
This document covers type testing only.
This document is also applicable to Gas Quick Connectors (GQC) for use inside appliances with
connections up to, and including DN 25, and a maximum operating pressure up to and including
100 kPa. GQCs include:
— tube to tube connections;
— tube to control connections; and
— tube to fitting connections.
This document does not apply to mechanical controls for use with liquid fuels. It is also not applicable to
corrosive and waste gases.
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 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances
and designation
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
100 IRHD)
ISO 65, Carbon steel tubes suitable for screwing in accordance with ISO 7-1
ISO 188, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
ISO 228-1, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions,
tolerances and designation
ISO 262, ISO general purpose metric screw threads — Selected sizes for screws, bolts and nuts
ISO 815, Rubber, vulcanized or thermoplastic — Determination of compression set — Part 1: At ambient or
elevated temperatures
ISO 1400, Vulcanized rubbers of high hardness (85 to 100 IRHD) — Determination of hardness
ISO 1431-1, Rubber, vulcanized or thermoplastic — Resistance to ozone cracking — Part 1: Static and
dynamic strain testing
ISO 1817, Rubber, vulcanized or thermoplastic — Determination of the effect of liquids
ISO 7005-1, Pipe flanges — Part 1: Steel flanges for industrial and general service piping systems
ISO 7005-2, Metallic flanges — Part 2: Cast iron flanges
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60730-1, Automatic electrical controls — Part 1: General requirements
IEC 60079-11, Explosive atmospheres — Part 11: Equipment protection by intrinsic safety "i"
IEC 61643-11, Low-voltage surge protective devices — Part 11: Surge protective devices connected to low-
voltage power systems - Requirements and test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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 https: //www .electropedia .org/
3.1
breather hole
orifice which allows atmospheric pressure to be maintained within a compartment of variable volume
3.2
closure member
movable part of the control (3.3) which shuts off the gas flow
3.3
control
device which directly or indirectly controls the gas flow and/or provides a safety function within a
burner or gas-burning appliance
3.4
external leak-tightness
leak-tightness of a gas-carrying compartment with respect to the atmosphere
2 © ISO 2018 – All rights reserved

3.5
internal leak-tightness
leak-tightness of the closure member (3.2) (in the closed position) sealing a gas-carrying compartment
with respect to another compartment or to the outlet of the control (3.3)
3.6
inlet pressure
pressure at the inlet of the control (3.3)
3.7
outlet pressure
pressure at the outlet of the control (3.3)
3.8
pressure difference
difference between the inlet pressure (3.6) and the outlet pressure (3.7)
3.9
operating pressure
pressure at which the control (3.3) operates
3.10
maximum operating pressure
highest inlet pressure declared by the manufacturer at which the control (3.3) may be operated
3.11
flow rate
volume flowing through the control (3.3) divided by time
3.12
rated flow rate
air flow rate (3.11) at a specified pressure difference declared by the manufacturer, corrected to
standard conditions
3.13
maximum ambient temperature
highest temperature of the surrounding air declared by the manufacturer at which the control (3.3)
may be operated
3.14
minimum ambient temperature
lowest temperature of the surrounding air declared by the manufacturer at which the control (3.3) may
be operated
3.15
mounting position
position declared by the manufacturer for mounting the control (3.3)
Note 1 to entry: Mounting positions are for example as follows:
— upright: single position on a horizontal axis with respect to the inlet connection, as specified by the
manufacturer;
— horizontal: any position on a horizontal axis with respect to the inlet connection;
— vertical: any position on a vertical axis with respect to the inlet connection;
— limited horizontal: any position from upright to 90° (1,57 rad) from upright on a horizontal axis with respect
to the inlet connection;
— multi-positional (multipoise): any position on a horizontal, vertical or intermediate axis with respect to the
inlet connection.
3.16
diameter nominal
DN
nominal size
alphanumeric designation of size for components of a pipework system, which is used for reference
purposes, comprising the letters DN followed by a dimensionless whole number which is indirectly
related to the physical size, in millimetres, of the bore or outside diameter of the end connections
Note 1 to entry: The number following the letters DN does not represent a measurable value and should not be
used for calculation purposes except where specified in the relevant standard.
Note 2 to entry: In those standards which use the DN designation system, any relationship between DN and
component dimensions should be given, e.g. DN/OD or DN/ID.
[SOURCE: ISO 6708:1995, 2.1, modified — The two sentences have been merged into one.]
3.17
type testing
conformity testing on the basis of one or more specimens of a product representative of the production
[SOURCE: ISO 8655-1:2002, 3.2.2]
3.18
main diaphragm
flexible member which, under the influence of the forces arising from loading and pressure, operates
the control member
3.19
gas quick connector
GQC
connector consisting of fastener (3.20), socket (3.21), plug (3.22) and seal (3.23)
Note 1 to entry: Specific requirements for GQCs are found in Annex D.
3.20
fastener
clip retaining the connection of plug (3.22) and socket (3.21)
3.21
socket
outside part of the GQC (3.19)
3.22
plug
inside part of the GQC (3.19)
3.23
seal
gas seal between the socket (3.21) and the plug (3.22)
3.24
sealing cap
removable cover or device that allows access to make adjustments to the control (3.3)
3.25
auxiliary channel
passageway that supports the intended function of the control (3.3)
3.26
vent limiter
device to limit leakage to atmosphere
4 © ISO 2018 – All rights reserved

3.27
pre-setting device
device for adjusting an operating condition
3.28
installation and operating instructions
manufacturer's information to install, operate and maintain the control
4 Classification
4.1 Classes of control
Where appropriate, controls are classified for the application (for example. construction or performance
characteristics, number of operations during their working life). For classification of controls, see the
specific control standard.
4.2 Groups of controls
Controls are grouped according to the bending stresses which they are required to withstand (see
Table 7):
a) Group 1 controls — Controls with connection sizes up to and including DN 25, for use in an
appliance where they are not subjected to bending stresses imposed by installation pipe work or in
an installation if used with rigid adjacent supports.
NOTE 1 In Canada, Japan and the USA, group 1 controls are not used.
b) Group 2 controls — Controls for use in any situation, either internal or external to the appliance,
typically without support.
NOTE 2 Controls which meet the requirements of group 2 control also meet the requirements of group 1
control.
4.3 Types of DC supplied controls
DC supplied controls are classified in one of the three following types:
— Type A: Stand-alone battery systems;
— Type B: Battery systems for non-stationary applications (i.e. applications which are changing
location or in motion);
— Type C: Systems which are intended to be connected to DC supply networks.
4.4 Classes of control functions
Classes of control functions are only applicable to functions consisting fully or partly out of electronics.
For the evaluation of protective measures for fault tolerance and avoidance of hazards, it is necessary
to classify control functions with regard to their fault behaviour.
At the classification of control functions, their integration into the complete safety concept of the
appliance shall be taken into account.
For the purpose of evaluating the design of a control function, the present requirements recognize
three distinct classes according IEC 60730-1:2013, H.2.22, as follows:
— Class A control function: Control functions which are not intended to be relied upon for the safety
of the application.
— Class B control function: Control functions which are intended to prevent an unsafe state of the
appliance. Failure of the control function does not lead directly to a hazardous situation.
— Class C control function: Control functions which are intended to prevent special hazards such as
explosion or whose failure can directly cause a hazard in the appliance.
This classification shall be specified in every product standard.
5 Test conditions and tolerances
5.1 Test conditions
Unless otherwise stated, the tests shall be carried out
— with air at (20 ± 5) °C; and
— at ambient temperature (20 ± 5) °C.
All measured values shall be corrected to standard conditions: 15 °C, 101,325 kPa (1 013,25 mbar) dry.
NOTE Specific regional requirements are given in H.2.1.
All measurements shall be made after stable conditions have been reached.
Controls which can be converted to another gas type by exchanging components are additionally tested
with the conversion components.
Tests shall be carried out in the mounting position as stated in the installation and operating
instructions. When multiple mounting positions are specified, tests shall be conducted with the control
in the least favourable position.
Where possible, the tests already covered by other standards (e.g. by relevant parts of IEC 60730-1)
shall be combined with tests presented in this document.
5.2 Tolerances
Unless otherwise stated in specific clauses, measurements shall be carried out with the maximum
tolerances indicated below:
— Absolute pressure ±4 %;
— Relative pressure ±2 % of the measured value, whichever is greater (e.g. gauge pressures or
differential pressures);
— Flow rate ±3 % of the measured value;
— Leakage rate ±10 cm /h (the apparatus shown schematically in Annex B or another device giving
equivalent results is used.);
— Time ±0,1 % or ±0,2 s, whichever is greater;
— Temperatures ±1,5 K;
— Torque ±10 %;
— Force ±10 %;
— Current ±1 %;
— Voltage ±1 %;
— Electrical power ±2 %;
6 © ISO 2018 – All rights reserved

— Supply frequency ±0,1 Hz.
The full range of the measuring apparatus is chosen to be suitable for maximum anticipated value.
For uncertainty of measurements, refer to ISO/IEC Guide 98-3.
6 Construction
6.1 General
Controls shall be designed, manufactured and assembled so that the various functions operate correctly
when installed and used according to the installation and operating instructions.
All pressurized parts of a control shall withstand the mechanical and thermal stresses to which they
are subjected without any deformation affecting safety.
In general, conformity with the requirements given in ISO/IEC International Standards is verified by:
— the test methods given therein or in the specific control standards; or
— the use of the construction materials specified in the requirements.
Depending on the class of control function in 4.4, the control shall be tested according to the electrical
requirements of the relevant clauses of IEC 60730-1:2013, Annex H.
6.2 Construction requirements
6.2.1 Appearance
6.2.1.1 General
Controls shall be suitable for the intended use. Handling, installation and maintenance shall be possible
without special equipment.
6.2.1.2 Requirements
Controls shall be fre
...