SIST EN 257:2010
(Main)Mechanical thermostats for gas-burning appliances
Mechanical thermostats for gas-burning appliances
This European Standard specifies the safety, construction and performance requirements for mechanical thermostats intended for use with gas appliances and similar use, hereafter referred to as ‘thermostats’. This European Standard applies to thermostats with declared maximum inlet pressures up to and including 50 kPa (500 mbar) of nominal connection sizes up to and including DN 50 for use with one or more fuel gases in accordance with EN 437. This European Standard applies to thermostats controlling the gas flow directly or indirectly through an integral gas valve, and which do not require external electrical energy for their operation. This European Standard only applies to thermostats used with gas appliances which are not installed in the open air. Thermostats dealt with in this European Standard are intended for control functions.
Mechanische Temperaturregler für Gasgeräte
Diese Europäische Norm legt die Anforderungen an die Sicherheit, konstruktive Ausführung und Funktion von
mechanischen Temperaturreglern fest, im Folgenden als ‚Temperaturregler’ bezeichnet, die für die
Verwendung mit Gasgeräten und ähnliche Verwendungszwecke vorgesehen sind.
Die vorliegende Europäische Norm gilt nur für die Typprüfung.
Sie gilt für Temperaturregler, die den Gasstrom direkt oder indirekt durch ein eingebautes Gasventil steuern
und für deren Betrieb keine äußere elektrische Energie erforderlich ist.
Sie gilt für Temperaturregler mit Nenn-Anschlussmaßen bis einschließlich DN 50 mit einem höchsten
angegebenen Eingangsdruck bis einschließlich 500 mbar (50 kPa) für die Verwendung mit einem oder
mehreren Brenngasen nach EN 437.
Sie gilt nur für Temperaturregler, die in Gasgeräten verwendet werden, die nicht im Freien aufgestellt sind.
Die in der vorliegenden Norm behandelten Temperaturregler sind für Regel- und Steuerfunktionen
vorgesehen.
Robinets automatiques de sectionnement pour brûleurs à gaz et appareils à gaz
La présente Norme européenne spécifie les caractéristiques de sécurité, de construction et de
fonctionnement des thermostats mécaniques équipant les appareils d’utilisation des combustibles gazeux et
utilisation similaire, ci-après désignés « thermostats ».
La présente Norme européenne ne couvre que les essais de type.
Elle s’applique aux thermostats qui contrôlent l’écoulement du gaz directement ou indirectement au moyen
d’une vanne de gaz intégrée et ne recourent pas à une énergie électrique extérieure pour leur
fonctionnement.
Elle s’applique aux thermostats de diamètres nominaux de raccordement jusqu’à et y compris DN 50 avec
pressions amont maximales déclarées jusqu’à et y compris 500 mbar (50 kPa) utilisés avec un ou plusieurs
combustibles gazeux conformément à l’EN 437.
Cette norme s’applique seulement aux thermostats utilisés sur des appareils d’utilisation des combustibles
gazeux qui ne sont pas installés à l’air libre.
Les thermostats visés par la présente norme assurent des fonctions de régulation.
Mehanski termostati za plinske aparate
Ta evropski standard določa zahteve za varnost, konstrukcijo in delovanje mehanskih termostatov, namenjenih za uporabo s plinskimi aparati in za podobno uporabo, v nadaljevanju »termostati«. Ta evropski standard velja za termostate z nazivnimi maksimalnimi vhodnimi tlaki do in vključno 50 kPa (500 mbar), nazivnih velikosti priključkov do in vključno DN 50, za uporabo z enim ali več kurilnih plinov v skladu z EN 437. Ta evropski standard velja za termostate, ki nadzorujejo pretok plina neposredno ali posredno preko vgrajenega plinskega ventila in ki ne potrebujejo zunanje električne energije za svoje delovanje. Ta evropski standard velja zgolj za termostate, ki se uporabljajo z plinskimi aparati, ki niso vgrajeni na prostem. Termostati, ki jih obravnava ta evropski standard, so namenjeni za nadzorne funkcije.
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Mehanski termostati za plinske aparateMechanische Temperaturregler für GasgeräteRobinets automatiques de sectionnement pour brûleurs à gaz et appareils à gazMechanical thermostats for gas-burning appliances27.060.20Plinski gorilnikiGas fuel burners17.200.20Instrumenti za merjenje temperatureTemperature-measuring instrumentsICS:Ta slovenski standard je istoveten z:EN 257:2010SIST EN 257:2010en,fr,de01-november-2010SIST EN 257:2010SLOVENSKI
STANDARDSIST EN 257:1997/A1:1997SIST EN 257:19971DGRPHãþD
SIST EN 257:2010
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 257
June 2010 ICS 27.060.20 Supersedes EN 257:1992English Version
Mechanical thermostats for gas-burning appliances
Thermostats mécaniques pour appareils à gaz
Mechanische Temperaturregler für Gasgeräte This European Standard was approved by CEN on 19 May 2010.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2010 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 257:2010: ESIST EN 257:2010
EN 257:2010 (E) 2 Contents Page Foreword .41Scope .52Normative references .53Terms and definitions .54Classification .75Units of measurement and test conditions .76Construction requirements .77Performance . 108EMC/Electrical requirements . 209Marking, installation and operating instructions . 21Annex A (informative)
Gas connections in common use in the various countries . 23Annex B (informative)
Leak-tightness test — volumetric method . 24Annex C (informative)
Leak-tightness test — pressure loss method . 25Annex D (normative)
Conversion of pressure loss into leakage rate . 26Annex E (normative)
Electrical/electronic component fault modes . 27Annex F (normative)
Additional requirements for safety accessories and pressure accessories as defined in EU Directive 97/23/EC. 28Annex G (normative)
Materials for pressurized parts . 29Annex H (informative)
Additional materials for pressurized parts . 30Annex I (normative)
Requirements for controls used in DC supplied gas burners and gas burning appliances . 31Annex ZA (informative)
Relationship between this European Standard and the Essential Requirements of EU Directive 2009/142/EC relating to appliances burning gaseous fuels . 32Bibliography . 34 SIST EN 257:2010
EN 257:2010 (E) 3 Figures Figure 1 — Thermostat test apparatus . 16 Figure 2 — Typical operating characteristics of a thermostat over a range of temperature set-point adjustments . 17
Tables Table 1 — Sequence of testing . 10Table 2 — Maximum leakage rates . 12Table 3 — Exceptions for thermal overload . 18Table 4 — Number of mechanical cycles . 20Table ZA.1 — Correspondence between this European Standard and Directive 2009/142/EC relating to appliances burning gaseous fuels . 32 SIST EN 257:2010
EN 257:2010 (E) 4 Foreword This document (EN 257:2010) has been prepared by Technical Committee CEN/TC 58 “Safety and control devices for burners and appliances burning gaseous or liquid fuels”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by December 2010, and conflicting national standards shall be withdrawn at the latest by December 2010. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive. For relationship with EU Directive, see informative Annex ZA, which is an integral part of this document. This document supersedes EN 257:1992. This European Standard is intended to be used in conjunction with EN 13611:2007. This document refers to clauses of EN 13611:2007 or adapts clauses by stating “with the following modification”, “with the following addition”, “is replaced by the following” or "is not applicable" in the corresponding clause. This European Standard adds clauses or sub clauses to the structure of EN 13611:2007 which are particular to this European Standard. It should be noted that these clauses and sub-clauses are not indicated as an addition. It should be noted that the following significant technical changes compared to the previous edition have been incorporated in this European Standard: a) scope is enlarged to maximum inlet pressures up to and including 50 kPa (500 mbar); b) alignment with EN 13611:2007; c) updating of Clause 2, normative references; d) units of measurement and test conditions are updated according to EN 13611:2007; e) requirements and tests concerning durability of elastomers in contact with gas (7.8 of this European Standard) are now totally aligned with EN 13611:2007, 7.8; f) marking, installation and operating instructions (Clause 9 of this European Standard) are extended to cover additional information. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. SIST EN 257:2010
EN 257:2010 (E) 5 1 Scope This European Standard specifies the safety, construction and performance requirements for mechanical thermostats intended for use with gas appliances and similar use, hereafter referred to as ‘thermostats’. This European Standard applies to thermostats with declared maximum inlet pressures up to and including
50 kPa (500 mbar) of nominal connection sizes up to and including DN 50 for use with one or more fuel gases in accordance with EN 437. This European Standard applies to thermostats controlling the gas flow directly or indirectly through an integral gas valve, and which do not require external electrical energy for their operation. This European Standard only applies to thermostats used with gas appliances which are not installed in the open air. Thermostats dealt with in this European Standard are intended for control functions. 2 Normative references The following referenced documents are indispensable for the application 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. EN 13611:2007, Safety and control devices for gas burners and gas-burning appliances — General require-ments 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN 13611:2007 and the following apply. 3.101 mechanical thermostat thermostat which controls the temperature by adjusting the flow rate accordingly to the temperature of the sensor without any external energy, such that the temperature remains within defined limits 3.102 adjustable thermostat mechanical thermostat in which the temperature set-point can be adjusted by the user to anywhere between minimum and maximum values 3.103 fixed setting thermostat mechanical thermostat that has a preset fixed operating temperature which cannot be adjusted by the user 3.104 snap-acting thermostat mechanical thermostat with only two positions for the flow rate, i.e. ‘full on-off’, ‘full on-reduced rate’ or ‘reduced rate-off’ 3.105 modulating thermostat mechanical thermostat which controls the flow rate in accordance with a predetermined and continuous function of the temperature of the temperature sensor SIST EN 257:2010
EN 257:2010 (E) 6 3.106 modulating thermostat with additional on-off action mechanical thermostat which acts as a snap-acting thermostat between the closed and reduced positions and as a modulating thermostat between the reduced and full-on positions 3.107 thermostat closure member movable part of the thermostat which opens and closes the gas way and/or varies the flow rate 3.108 presetting device device for adjusting an operating condition only by an authorized person NOTE It may be fixed or variable, e.g. when it is the gas flow that is adjustable, either an orifice or an adjusting screw may be used. 3.109 fixed bypass non-adjustable presetting device for fixing the minimum gas flow through a thermostat 3.110 bypass adjusting device screw adjustment or an exchangeable orifice, that fixes the minimum gas flow rate through the thermostat, and which is accessible only by the use of tools 3.111 temperature sensor device which senses the temperature of the medium to be controlled or to be supervised 3.112 operating curve graphical representation of the flow rate as a function of the sensor temperature at a given temperature set-point and at a constant inlet pressure 3.113 backlash difference of position of the adjusting knob when it is moved in both directions to obtain the same flow rate at a constant sensor temperature 3.114 adjusting knob (or spindle) part of the thermostat which is used to select the temperature set-point 3.115 temperature set-point any value selected within the temperature range at which the controlled temperature should be maintained 3.116 temperature set-point range range between the minimum and maximum adjustable temperature set-points (by means of the adjusting knob) 3.117 calibration flow rate flow rate declared by the manufacturer for calibration 3.118 calibration temperature set-point temperature at which the calibration flow rate should be obtained with the adjustment set to the position and in the direction declared by the manufacturer SIST EN 257:2010
EN 257:2010 (E) 7 3.119 temperature differential for snap-acting thermostats difference in temperature necessary to obtain a change in the flow rate, at a given set-point 3.120 deviation maximum deviation from the temperature set-point which is declared by the manufacturer 3.121 drift permanent change in the operating curve of the thermostat 4 Classification 4.1 Classes of control EN 13611:2007, 4.1 is not applicable. 4.2 Groups of control Shall be according to EN 13611:2007, 4.2. 4.3
Classes of control functions EN 13611:2007, 4.3 is not applicable. 5 Units of measurement and test conditions Shall be according to EN 13611:2007, Clause 5. 6 Construction requirements 6.1 General Shall be according to EN 13611:2007, 6.1. 6.2 Mechanical parts of the control 6.2.1 Appearance Shall be according to EN 13611:2007, 6.2.1. 6.2.2 Holes Shall be according to EN 13611:2007, 6.2.2. 6.2.3 Breather holes Shall be according to EN 13611:2007, 6.2.3. SIST EN 257:2010
EN 257:2010 (E) 8 6.2.4 Test for leakage of breather holes Shall be according to EN 13611:2007, 6.2.4. 6.2.5 Screwed fastenings Shall be according to EN 13611:2007, 6.2.5. 6.2.6 Jointing Shall be according to EN 13611:2007, 6.2.6. 6.2.7 Moving parts Shall be according to EN 13611:2007, 6.2.7. 6.2.8 Sealing caps Shall be according to EN 13611:2007, 6.2.8. 6.2.9 Dismantling and reassembly Shall be according to EN 13611:2007, 6.2.9 with the following addition: If, in accordance with the manufacturers instructions the thermostat can be dismantled for servicing, such action shall not result in a change in temperature calibration exceeding the declared maximum set point deviation (see 7.101.1). 6.2.101 Presetting devices A presetting device shall only be adjustable by use of a tool. The means of adjustment shall be easily accessible and shall not change of its own accord, but shall be protected against unauthorized interference, e.g. use of a sealing (lacquer). A presetting device which connects a gas-carrying part to atmosphere shall be made sound by a means which shall not seal on the thread, e.g. use of an O-ring seal. The presetting device shall not be able to fall into the gas ways of the thermostat. If an O-ring or equivalent gasket provides a seal against the atmosphere, then when the presetting device is completely unscrewed it shall not be able to be pushed out by gas pressure and shall remain tight at the maximum pressure specified in 7.3. If a presetting device is used for different gas families it shall have a fixed minimum orifice. A cover of any presetting device shall require a tool for removal and replacement and it shall not interfere with the adjustment of the temperature range. 6.3 Materials Shall be according to EN 13611:2007, 6.3. 6.4 Gas connections 6.4.1 Making connections Shall be according to EN 13611:2007, 6.4.1. SIST EN 257:2010
EN 257:2010 (E) 9 6.4.2 Connection sizes Shall be according to EN 13611:2007, 6.4.2. 6.4.3 Threads Shall be according to EN 13611:2007, 6.4.3. 6.4.4 Union joints Shall be according to EN 13611:2007, 6.4.4. 6.4.5 Flanges Shall be according to EN 13611:2007, 6.4.5. 6.4.6 Compression fittings Shall be according to EN 13611:2007, 6.4.6. 6.4.7 Nipples for pressure test Shall be according to EN 13611:2007, 6.4.7. 6.4.8 Strainers Shall be according to EN 13611:2007, 6.4.8. 6.4.101 Flow characteristics An adjustable bypass shall be set by means of a variable presetting device or shall be adjusted by means of a fixed presetting device. It shall be possible to gain access to any fixed bypass or bypass adjusting device for cleaning without changing the calibration temperature set-point. The opening and closing of the thermostat closure member with a total shut-off function shall happen by snap-action between the off position and the reduced flow position. Figure 2 shows typical operating curves of a modulating, snap-acting and modulating on-off thermostat. The flow rate at the moment of snap-action shall not be less than the value as stated in the operating instructions. 6.4.102 Temperature adjustment 6.4.102.1 Range adjustment The allowed temperature setting range shall be limited by stops. Where applicable the operating instructions shall state the limits in which the temperature setting range may be adjusted using appropriate tools. The temperature setting range stops shall not change on their own accord.
6.4.102.2 Set point adjustment If the adjusting knob is supplied as part of the thermostat, the marking of its positions shall be easily recognizable. It shall indicate the direction in which the temperature is raised or lowered. If numbers are used, SIST EN 257:2010
EN 257:2010 (E) 10 higher numbers shall indicate higher temperatures, except for thermostats for refrigerators where higher numbers shall indicate lower temperatures. It shall be possible to select any temperature set-point over the whole temperature range by setting the adjusting knob or spindle between the stops within the maximum and minimum ambient temperatures as stated in the operating instructions. The temperature setting means shall not change on its own accord. 6.4.102.3 Fixed setting thermostat If provided, the adjuster of a fixed setting thermostat shall be sealed (e. g. lacquer). 6.5 Electronic parts of the control EN 13611:2007, 6.5 is not applicable. 6.6 Protection against internal faults for the purpose of functional safety EN 13611:2007, 6.6 is not applicable. 7 Performance
7.1 General Shall be according to EN 13611:2007, 7.1 with the following addition: Tests shall be conducted in the sequence shown in Table 1. Table 1 — Sequence of testing Clause Test Thermostat number 1 2 7.2 / 7.3 Leak-tightness / Test for leak-tightness (except 6.3.2 / 6.3.3) X X 7.107 Effect of storage and transport temperatures X
7.108 Thermal overload of the temperature sensor X
7.101 Calibration temperature set-point X X 7.106 Ambient temperature range of the body
X 7.102 Backlash X X 7.6 / 7.7 Rated flow rate / Test for rated flow rate
X 7.105 Operating characteristic of the thermostat
X 7.103 Opening of snap-acting thermostat with a closed position
X 7.104 Opening pressure and closing pressure for thermostats with a closed position X
7.109 Operating torque of the thermostat set-point adjuster X X 7.4 / 7.5 Torsion and bending / Torsion and bending tests X
SIST EN 257:2010
EN 257:2010 (E) 11 Clause Test Thermostat number 1 2 7.2 / 7.3 Leak-tightness / Test for leak-tightness (except 6.3.2 / 6.3.3) X
7.110 / 7.110.2.1 Endurance / Mechanical cycling test X
7.110 / 7.110.2.2 Endurance / Thermal cycling test
X 7.109 Operating torque of the thermostat set-point adjuster X
7.102 Backlash X
7.2 / 7.3 Leak-tightness / Test for leak-tightness (except 6.3.2 / 6.3.3) X X 7.101 Calibration temperature set-point X X 7.8.4, 7.8.5, 7.8.6, and 7.8.7 of EN 13611:2007 Resistance to scratching / Scratch test / Resistance to humidity / Humidity test X
7.101 / 7.105 Calibration temperature set-point / Operating characteristic of the thermostat
X 6.3.2 / 6.3.3 Housing / Test for leakage of housing after removal of non-metallic parts
X Thermostats which can be converted to other gas families by exchange of parts shall be supplied with these parts.
7.2 Leak-tightness EN 13611:2007, 7.2 is replaced by the following: Thermostats shall be leak-tight in accordance with the leakage rates given in Table 2. SIST EN 257:2010
EN 257:2010 (E) 12 Table 2 — Maximum leakage rates Nominal size (inlet) DN Maximum leakage rate cm3/h of air Internal leak-tightness a External leak-tightness DN < 10
60 20 10 ≤ DN ≤ 15
60 40 15 < DN ≤ 25
80 40 25 < DN ≤ 50 120 60 a This requirement applies only to thermostats with complete shut-off.
7.3 Test for leak-tightness 7.3.1 General Shall be according to EN 13611:2007, 7.3.1. 7.3.2 External leak-tightness Shall be according to EN 13611:2007
...
SLOVENSKI STANDARD
oSIST prEN 257:2008
01-november-2008
Mehanski termostati za plinske aparate
Mechanical thermostats for gas-burning appliances
Mechanische Temperaturregler für Gasgeräte
Robinets automatiques de sectionnement pour brûleurs à gaz et appareils à gaz
Ta slovenski standard je istoveten z: prEN 257
ICS:
17.200.20 Instrumenti za merjenje Temperature-measuring
temperature instruments
oSIST prEN 257:2008 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 257:2008
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oSIST prEN 257:2008
EUROPEAN STANDARD
DRAFT
prEN 257
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2008
ICS 17.200.20 Will supersede EN 257:1992
English Version
Mechanical thermostats for gas-burning appliances
Robinets automatiques de sectionnement pour brûleurs à Mechanische Temperaturregler für Gasgeräte
gaz et appareils à gaz
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 58.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other language
made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the
same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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 supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 257:2008: E
worldwide for CEN national Members.
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oSIST prEN 257:2008
prEN 257:2008 (E)
Contents Page
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms and definitions .4
4 Classification.8
5 Units of measurement and test conditions.9
6 Construction requirements.9
7 Performance .12
8 EMC/Electrical requirements.22
9 Marking, installation and operating instructions .23
Annex A (informative) Gas connections in common use in the various countries.25
Annex B (informative) Leak-tightness test — volumetric method .26
Annex C (informative) Leak-tightness test — pressure loss method .27
Annex D (normative) Conversion of pressure loss into leakage rate .28
Annex E (normative) Electrical/electronic component fault modes.29
Annex F (normative) Additional requirements for safety accessories and pressure accessories
as defined in EU Directive 97/23/EC.30
Annex G (normative) Materials for pressurized parts.31
Annex H (informative) Additional materials for pressurized parts.32
Annex I (normative) Requirements for controls used in DC supplied gas burners and gas
burning appliances.33
Annex ZA (informative) Clauses of this European Standard addressing essential requirements or
other provisions of EU Directives.34
Bibliography .36
2
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oSIST prEN 257:2008
prEN 257:2008 (E)
Foreword
This document (prEN 257:2008) has been prepared by Technical Committee CEN/TC 58 “Safety and control
devices for gas-burners and gas-burning appliances”, the secretariat of which is held by BSI.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 257:1992.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EC Directive(s).
For relationship with EC Directive(s), see informative Annex ZA, which is an integral part of this document.
This document is intended to be used in conjunction with EN 13611:2007. This document refers to clauses of
EN 13611:2007 or adapting it by stating “Addition”, “Modification” or “Replacement” in the corresponding
clause.
Note that the following provides details of significant technical changes between this European Standard and
the previous edition:
a) scope is enlarged to maximum inlet pressures up to and including 500 mbar (50 kPa);
b) alignment with EN 13611:2007;
c) updating of clause 2, normative references;
d) units of measurement and test conditions are updated according to EN 13611:2007;
e) although thermostats, which do not require external electrical energy for their operation, are not covered
by this standard, clauses 6.5 (Electronic parts of the control) and 6.6 (Protection against internal faults for
the purpose of functional safety) are added according to EN 13611:2007 to cover requirements and tests
for thermostats using internal electrical energy, if applicable;
f) requirements and tests concerning durability of elastomers in contact with gas (clause 7.8 of this
standard) are completely aligned to EN 13611:2007, which refers to EN 549;
g) marking, installation and operating instructions (clause 9 of this standard) are extended to some more
information;
h) annexes E to I are added according to EN 13611:2007.
3
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oSIST prEN 257:2008
prEN 257:2008 (E)
1 Scope
This European Standard specifies the safety, construction and performance requirements for mechanical
thermostats intended for use with gas appliances and similar use, hereafter referred to as ‘thermostats’.
This European Standard covers type testing only.
It applies to thermostats controlling the gas flow directly or indirectly through an integral gas valve, and which
do not require external electrical energy for their operation.
It applies to thermostats of nominal connection sizes up to and including DN 50 with declared maximum inlet
pressures up to and including 500 mbar (50 kPa) for use with one or more fuel gases in accordance with EN
437.
It only applies to thermostats used with gas appliances which are not installed in the open air.
Thermostats dealt with in this standard are intended for control functions.
2 Normative references
The following referenced documents are indispensable for the application 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.
EN 13611:2007, Safety and control devices for gas burners and gas-burning appliances — General require-
ments
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
control
[EN 13611:2007, 3.1]
3.2
control function
[EN 13611:2007, 3.2]
3.3
closure member
[EN 13611:2007, 3.3]
3.4
external leak-tightness
[EN 13611:2007, 3.4]
3.5
internal leak-tightness
[EN 13611:2007, 3.5]
3.6
inlet pressure
[EN 13611:2007, 3.6]
4
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oSIST prEN 257:2008
prEN 257:2008 (E)
3.7
outlet pressure
[EN 13611:2007, 3.7]
3.8
pressure difference
[EN 13611:2007, 3.8]
3.9
maximum inlet pressure
[EN 13611:2007, 3.9]
3.10
minimum inlet pressure
[EN 13611:2007, 3.10]
3.11
flow rate
[EN 13611:2007, 3.11]
3.12
rated flow rate
[EN 13611:2007, 3.12]
3.13
maximum ambient temperature
[EN 13611:2007, 3.13]
3.14
minimum ambient temperature
[EN 13611:2007, 3.14]
3.15
mounting position
[EN 13611:2007, 3.15]
3.16
nominal size DN
[EN 13611:2007, 3.16]
3.17
apparatus
[EN 13611:2007, 3.17]
3.18
system
[EN 13611:2007, 3.18]
3.19
installation
[EN 13611:2007, 3.19]
3.20
fault tolerating time
[EN 13611:2007, 3.20]
3.21
fault reaction time
[EN 13611:2007, 3.21]
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3.22
normal operation
[EN 13611:2007, 3.22]
3.23
defined state
[EN 13611:2007, 3.23]
3.24
complex electronics
[EN 13611:2007, 3.24]
3.25
reset
[EN 13611:2007, 3.25]
3.26
failure
[EN 13611:2007, 3.26]
3.27
degradation
[EN 13611:2007, 3.27]
3.28
fault
[EN 13611:2007, 3.28]
3.29
harm
[EN 13611:2007, 3.29]
3.30
hazard
[EN 13611:2007, 3.30]
3.31
risk
[EN 13611:2007, 3.31]
3.32
functional safety
[EN 13611:2007, 3.32]
3.33
program
[EN 13611:2007, 3.33]
3.34
breather hole
[EN 13611:2007, 3.34]
3.35
Types of thermostats
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3.35.1
mechanical thermostat
thermostat which controls the temperature by adjusting the flow rate accordingly to the temperature of the
sensor without any external energy, such that the temperature remains within defined limits, and which is
distinguished to the following types
3.35.2
adjustable thermostat
thermostat in which the temperature set-point can be adjusted by the user between minimum and maximum
values
3.35.3
fixed setting thermostat
thermostat that has a preset fixed operating temperature which cannot be adjusted by the user
3.35.4
snap-acting thermostat
thermostat with only two positions for the flow rate, i.e. ‘full on-off’, ‘fall on-reduced rate’ or ‘reduced rate-off’
3.35.5
modulating thermostat
thermostat which controls the flow rate in accordance with a predetermined and continuous function of the
temperature of the temperature sensor
3.35.6
modulating thermostat with additional on-off action
thermostat which acts as a snap-acting thermostat between the closed and reduced positions and as a
modulating thermostat between the reduced and full-on positions
3.36
thermostat closure member
movable part of the thermostat which opens and closes the gasway and/or varies the flow rate
3.37
presetting thermostat
thermostat for adjusting an operating condition only by an authorized person. It may be fixed or variable, e.g.
when it is the gas flow that is adjustable, either an orifice or an adjusting screw may be used
3.38
fixed bypass
non-adjustable presetting device for fixing the minimum gas flow through a thermostat
3.39
bypass adjusting device
screw adjustment or an exchangeable orifice, that fixes the minimum gas flow rate through the thermostat,
and which is accessible only by the use of tools
3.40
temperature sensor
device which senses the temperature of the medium to be controlled or to be supervised
3.41
operating curve
graphical representation of the flow rate as a function of the sensor temperature at a given temperature set-
point and at a constant inlet pressure
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3.42
backlash
difference of position of the adjusting knob when it is moved in both directions to obtain the same flow rate at
a constant sensor temperature
3.43
adjusting knob (or spindle)
part of the thermostat which is used to select the temperature set-point
3.44
temperature set-point
any value selected within the temperature range at which the controlled temperature should be maintained
3.45
temperature set-point range
range between the minimum and maximum adjustable temperature set-points (by means of the adjusting
knob)
3.46
calibration flow rate
flow rate declared by the manufacturer for calibration
3.47
calibration temperature set-point
temperature at which the calibration flow rate should be obtained with the adjustment set to the position and in
the direction declared by the manufacturer
3.48
temperature differential for snap-acting thermostats
difference in temperature necessary to obtain a change in the flow rate, at a given set-point
3.49
deviation
maximum deviation from the temperature set-point which is declared by the manufacturer
3.50
drift
permanent change in the operating curve of the thermostat
4 Classification
4.1 Classes of control
According to EN 13611:2007, 4.1.
Addition:
Thermostats are not classified.
4.2 Groups of control
According to EN 13611:2007, 4.2.
4.3 Classes of control functions
According to EN 13611:2007, 4.3.
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5 Units of measurement and test conditions
According to EN 13611:2007, Clause 5.
6 Construction requirements
6.1 General
According to EN 13611:2007, 6.1.
Addition:
Thermostats shall shut off automatically the gas way to the burner with at least the sealing force specified in
7.14 in case of failure in the thermoelectric current.
Thermostats shall be designed so that during ignition either the gas way to the main burner is open, if there is
no pilot burner, or the gas way to the main burner is closed, and that to the pilot burner is open.
6.2 Mechanical parts of the control
6.2.1 Appearance
According to EN 13611:2007, 6.2.1.
6.2.2 Holes
According to EN 13611:2007, 6.2.2.
6.2.3 Breather holes
EN 13611:2007, 6.2.3 is not applicable.
6.2.4 Test for leakage of breather holes
EN 13611:2007, 6.2.4 is not applicable.
6.2.5 Screwed fastenings
According to EN 13611:2007, 6.2.5.
6.2.6 Jointing
According to EN 13611:2007, 6.2.6.
6.2.7 Moving parts
According to EN 13611:2007, 6.2.7.
6.2.8 Sealing caps
According to EN 13611:2007, 6.2.8.
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6.2.9 Dismantling and reassembly
According to EN 13611:2007, 6.2.9.
Addition:
If the thermostat, according to the manufacturer’s instructions, can be dismantled in order to service it, the
operation to do this shall not cause any change to the temperature calibration exceeding the maximum
deviation at the calibration temperature set-point declared by the manufacturer (see 7.11.1).
6.2.10 Presetting thermostats
A presetting thermostat shall only be adjustable by a tool. It shall be easily accessible and shall not change of
its own accord, but it shall be protected against unauthorized interference, e.g. using a lacquer.
A presetting thermostat which connects a gas-carrying part to atmosphere shall be made sound by a means
which shall not seal on the thread, e.g. O-ring seal.
The presetting thermostat shall not be able to fall into the gasways of the thermostat. If an O-ring or equivalent
provides a seal against the atmosphere, then when the presetting thermostat is completely unscrewed it shall
not be able to be pushed out by gas pressure and shall remain tight at the higher pressure specified in 7.3.
If a presetting thermostat is used for different gas families it shall have a fixed minimum orifice.
Any cover of any presetting thermostat shall require a tool for removal and replacement and it shall not
interfere with the adjustment of the temperature range.
6.3 Materials
6.3.1 General material requirements
According to EN 13611:2007, 6.3.1.
6.3.2 Housing
According to EN 13611:2007, 6.3.2.
6.3.3 Test for leakage of housing after removal of non-metallic parts
According to EN 13611:2007, 6.3.3.
6.3.4 Zinc alloys
According to EN 13611:2007, 6.3.4.
6.3.5 Springs providing closing and/or sealing force
According to EN 13611:2007, 6.3.5.
6.3.6 Resistance to corrosion and surface protection
According to EN 13611:2007, 6.3.6.
6.3.7 Impregnation
According to EN 13611:2007, 6.3.7.
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6.3.8 Seals for glands for moving parts
According to EN 13611:2007, 6.3.8.
6.4 Gas connections
6.4.1 Making connections
According to EN 13611:2007, 6.4.1.
6.4.2 Connection sizes
According to EN 13611:2007, 6.4.2.
6.4.3 Threads
According to EN 13611:2007, 6.4.3.
6.4.4 Union joints
According to EN 13611:2007, 6.4.4.
6.4.5 Flanges
According to EN 13611:2007, 6.4.5.
6.4.6 Compression fittings
According to EN 13611:2007, 6.4.6.
6.4.7 Nipples for pressure test
According to EN 13611:2007, 6.4.7.
6.4.8 Strainers
According to EN 13611:2007, 6.4.8.
6.4.9 Flow characteristics
An adjustable bypass shall be adjustable by means of a variable presetting thermostat or shall be adjusted by
means of a fixed presetting thermostat.
It shall be possible to gain access to any fixed bypass or bypass adjusting device for cleaning without
changing the calibration temperature set-point.
The opening and closing of the closure member of a thermostat with a total shut-off function shall happen by
snap-action between the off position and the reduced flow position.
Figure 2 shows typical operating curves of a modulating, snap-acting and modulating on-off thermostat.
The flow rate at the moment of snap-action shall not be less than the value declared by the manufacturer.
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6.4.10 Temperature adjustment
6.4.10.1 Range adjustment
The allowed temperature setting range shall be limited by stops. Where applicable the manufacturer shall
declare the limits in which the temperature setting range may be adjusted using appropriate tools. The
temperature setting range stops shall not change of their own accord.
6.4.10.2 Set point adjustment
If the adjusting knob is supplied as part of the thermostat, the marking of its positions shall be easily
recognizable. It shall indicate the direction in which the temperature is raised or lowered. If numbers are used,
higher numbers shall indicate higher temperatures, except for thermostats for refrigerators where higher
numbers shall indicate lower temperatures.
It shall be possible to select any temperature set-point over the whole temperature range by setting the
adjusting knob or spindle between the stops within the maximum and minimum ambient temperatures
declared by the manufacturer.
The temperature setting means shall not change of its own accord.
6.4.10.3 Fixed setting thermostat
If provided, the adjuster of a fixed setting thermostat shall be sealed (e.g. lacquer).
6.5 Electronic parts of the control
According to EN 13611:2007, 6.5.
6.6 Protection against internal faults for the purpose of functional safety
According to EN 13611:2007, 6.6.
7 Performance
7.1 General
According to EN 13611:2007, 7.1.
Addition:
Tests shall be conducted to sequence shown in Table 1.
Table 1 — Sequence of testing
Thermostat
number
Clause Test
1 2
7.2 / 7.3 Leakage (except 6.3.2 / 6.3.3) X X
7.17 Effect of storage and transient temperatures X
7.18 Thermal overload of the temperature sensor X
7.11 Calibration temperature set-point X X
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Table 1 (continued)
Thermostat
number
Clause Test
1 2
7.16 Ambient temperature range of the body X
7.12 Backlash X X
7.6 / 7.7 Rated flow rate X
7.15 Operating characteristic of the thermostat X
7.13 Opening of snap-action thermostat with a closed position X
Opening pressure and closing pressure for thermostats with a
7.14 X
closed position
7.19 Operating torque of the thermostat set-point adjuster X X
7.4 / 7.5 Torsion and bending X
7.2 / 7.3 Leakage (except 6.3.2 / 6.3.3) X
7.20 / 7.20.2.1 Mechanical cycling test X
7.20 / 7.20.2.2 Thermal cycling test X
7.19 Operating torque of the thermostat set-point adjuster X
7.12 Backlash X
7.2 / 7.3 Leakage (except 6.3.2 / 6.3.3) X X
7.11
Calibration temperature set-point X X
7.8.4, 7.8.5, 7.8.6,
and 7.8.7 of Resistance to scratching and humidity X
EN 13611:2007
7.11.1 / 7.15 Calibration check X
6.3.2 / 6.3.3 Non-metallic housing parts (leak-tightness) X
NOTE Thermostats which can be converted to other gas families by exchange of parts shall be supplied with these
parts.
7.2 Leak-tightness
According to EN 13611:2007, 7.2.
Replacement:
Thermostats shall be leak-tight in accordance with the leakage rates given in Table 2.
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Table 2 — Maximum leakage rates
Maximum leakage rate
Nominal size
3
(inlet)
cm /h of air
DN
1)
Internal leak-tightness External leak-tightness
DN < 10 60 20
10 ≤ DN ≤ 15 60 40
15 < DN ≤ 25 80 40
25 < DN ≤ 50 120 60
1)
This requirement applies only to thermostats with complete shut-off.
7.3 Test for leak-tightness
7.3.1 General
According to EN 13611:2007, 7.3.1.
7.3.2 External leak-tightness
According to EN 13611:2007, 7.3.2.
7.3.3 Internal leak-tightness
According to EN 13611:2007, 7.3.3.
Addition:
This test applies only to thermostats with complete shut-off. The knob is set at the middle of its temperature
setting range and the temperature sensor is slowly heated (or cooled, for controls for refrigerators) until the
valve is closed. The temperature of the sensor is then increased (or decreased for refrigerators) by a value
equal to 10 % of the temperature range of the thermostat. The thermostat is then checked for internal leak-
tightness.
The test is carried out in the direction of gas flow.
7.4 Torsion and bending
According to EN 13611:2007, 7.4.
7.5 Torsion and bending tests
According to EN 13611:2007, 7.5.
7.6 Rated flow rate
According to EN 13611:2007, 7.6.
Replacement:
The rated flow rate and bypass flow rate shall be measured.
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The measured flow rate shall be at least 0,9 times the rated flow rate.
For thermostats with a variable preset bypass, the bypass flow rate shall be adjustable over the whole range
declared by the manufacturer. For thermostats with a fixed preset bypass, the bypass flow rate shall remain
within the tolerance limits declared by the manufacturer.
7.7 Test for rated flow rate
7.7.1 Apparatus
According to EN 13611:2007, 7.7.1.
7.7.2 Test procedure
According to EN 13611:2007, 7.7.2.
Replacement:
Rated flow rate and by-pass flow rate are taken from the operating curves as indicated in 7.15. The corrected
flow rate and the corrected rated bypass flow rate according to 7.7.3 shall comply with the requirements of
7.6.
7.7.3 Conversion of air flow rate
According to EN 13611:2007, 7.7.3.
7.8 Durability
According to EN 13611:2007, 7.8.
7.9 Performance tests for electronic controls
EN 13611:2007, 7.9 is not applicable.
7.10 Long-term performance for electronic controls
EN 13611:2007, 7.10 is not applicable.
7.11 Calibration temperature set-point
7.11.1 Requirement
The deviation of the calibration temperature set-point at constant ambient temperature shall not exceed the
value declared by the manufacturer.
7.11.2 Test for calibration temperature set-point
With the body at an ambient temperature of (20 ± 2) °C, the adjusting knob is set to the position and in the
direction indicated by the manufacturer for calibration. The operating characteristic of the thermostat is drawn
according to 7.15.2.
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7.12 Backlash
7.12.1 Requirement
The backlash shall not exceed 5 % of the angular movement of the setting point adjustment range of the
thermostat.
7.12.2 Test for backlash
The sensor is held at a constant temperature equal to the middle of the temperature range.
The thermostat is supplied with air at 20 mbar (2 kPa). The pressure difference with all the valves in the fully
open position is adjusted to 2,5 mbar (250 Pa).
During the test, the body of the thermostat is maintained at a constant ambient temperature within ± 1 °C.
Turn the range spindle from the minimum temperature set-point until the calibration flow rate is obtained and
record this position. Continue to turn the range spindle to the maximum temperature set-point and then turn
the spindle back again to the position at which the calibration flow rate is obtained. Record this position.
Measure the backlash which is the angular difference between these two positions.
This test is only applicable to modulating thermostats.
7.13 Opening of a snap-acting thermostat with a closed position
7.13.1 Requirement
The total leakage of a two-position thermostat (on-off) or of a modulating on-off thermostat during the opening
3
procedure up to the point of snap-action shall not exceed 1 dm of air.
7.13.2 Test for opening of a snap-acting thermostat with a closed position
The thermostat is supplied with air at 20 mbar (2 kPa). The pressure difference with all the valves in the fully-
open position is adjusted to 2,5 mbar (250 Pa).
During the test, the body of the thermostat is held at a constant ambient temperature within ± 1 °C.
The thermostat is set at the calibration temperature set-point indicated by the manufacturer. The temperature
sensor is immersed in a bath, the temperature of which is increased at a rate of 0,5 K/min until the thermostat
valve is closed. The temperature is then lowered at the rate of 0,5 K/min until the thermostat snaps open.
During the lowering of the temperature the total flow is measured from the temperature at which closure
occurred up to the moment of snap-action.
For a refrigeration thermostat the above temperature changes are reversed.
7.14 Opening pressure and closing pressure for thermostats with a closed position
7.14.1 Requirement
The thermostat shall be capable of opening and closing between the minimum and 1,2 times the maximum
inlet pressure declared by the manufacturer, but at least against a maximum pressure of 50 mbar (5 kPa).
7.14.2 Test for opening pressure and closing pressure for thermostats with a closed position
Using the equipment as shown in Figure 1, a pressure equal to 1,2 times the maximum inlet pressure, but at
least 50 mbar (5 kPa), is supplied to the inlet of the thermostat. The pressure drop, with the valve in the fully
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open position, is adjusted to 2,5 mbar (250 Pa). Check that the valve opens and closes at a temperature
change of the temperature sensor.
7.15 Operating characteristic of the thermostat
7.15.1 Requirement
When tested:
a) the temperature range shall be within the range and tolerances declared by the manufacturer;
b) the temperature differential U of a snap-acting or a modulating on-off thermostat shall lie within the
sd
range declared by the manufacturer;
c) the modulation band of thermostats shall lie within the range declared by the manufacturer.
7.15.2 Test for operating characteristic of the thermostat
The test shall be carried out using air at an inlet pressure of 20 mbar (2 kPa). The thermostat shall be
connected in the test equipment as indicated in Figure 1. The error in measurement shall be less than 2 %.
With the closure member(s) in the open position, the pressure difference is adjusted to 2,5 mbar (250 Pa) by
actuating valve no. 8 flow rate control. There shall be no further modification to this adjustment during the
tests described in this clause. The flow rate is then compared to the rated flow rate.
With the value of the modulating thermostat closed, t
...
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