Safety devices for protection against excessive pressure - Part 1: Safety valves (ISO 4126-1:2013)

This part of ISO 4126 specifies general requirements for safety valves irrespective of the fluid for which they are designed. It is applicable to safety valves having a flow diameter of 4 mm and above which are for use at set pressures of 0,1 bar gauge and above. No limitation is placed on temperature. This is a product standard and is not applicable to applications of safety valves.

Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 1: Sicherheitsventile (ISO 4126-1:2013)

Diese Europäische Norm legt allgemeine Anforderungen an Sicherheitsventile fest, unabhängig von dem Medium, für das sie ausgelegt sind.
Die Norm gilt für Sicherheitsventile mit einem engsten Strömungsdurchmesser von mindestens 4 mm und für Ansprech¬drücke von mindestens 0,1 bar. Temperaturgrenzen sind nicht festgelegt. Die vorliegende Norm ist eine Produktnorm und behandelt keine Anwendungsfälle für Sicherheitsventile.

Dispositifs de sécurité pour protection contre les pressions excessives - Partie 1: Soupapes de sûreté (ISO 4126-1:2013)

L'ISO 4126-1:2013 spécifie les exigences générales des soupapes de sûreté, quel que soit le fluide pour lequel elles sont conçues.
Elle est applicable aux soupapes de sûreté présentant un orifice d'écoulement de diamètre supérieur ou égal à 4 mm, qui sont utilisables à des pressions de début d'ouverture de 0,1 bar effectif et au-dessus. Aucune limitation en température n'est fixée.
L'ISO 4126-1:2013 est une norme de produit et elle n'est pas applicable à la mise en ?uvre des soupapes de sûreté.

Naprave za varovanje pred visokim tlakom - 1. del: Varnostni ventili (ISO 4126-1:2013)

Ta del standarda ISO 4126 določa splošne zahteve za varnostne ventile ne glede na tekočino, za katero so oblikovani. Uporablja se za varnostne ventile s premerom pretoka 4 mm in več, ki se uporabljajo pri nastavljenih tlakih 0,1 bara in več. Temperatura ni omejena. To je standard izdelka in ne velja za uporabo varnostnih ventilov.

General Information

Status
Published
Public Enquiry End Date
24-Mar-2010
Publication Date
25-Jul-2013
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
25-Jul-2013
Due Date
29-Sep-2013
Completion Date
26-Jul-2013

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Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 4126-1:2013
01-september-2013
1DGRPHãþD
SIST EN ISO 4126-1:2004
SIST EN ISO 4126-1:2004/AC:2007
Naprave za varovanje pred visokim tlakom - 1. del: Varnostni ventili (ISO 4126-
1:2013)
Safety devices for protection against excessive pressure - Part 1: Safety valves (ISO
4126-1:2013)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 1: Sicherheitsventile (ISO
4126-1:2013)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 1:
Soupapes de sûreté (ISO 4126-1:2013)
Ta slovenski standard je istoveten z: EN ISO 4126-1:2013
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
SIST EN ISO 4126-1:2013 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN ISO 4126-1:2013

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SIST EN ISO 4126-1:2013


EUROPEAN STANDARD
EN ISO 4126-1

NORME EUROPÉENNE

EUROPÄISCHE NORM
July 2013
ICS 13.240 Supersedes EN ISO 4126-1:2004
English Version
Safety devices for protection against excessive pressure - Part
1: Safety valves (ISO 4126-1:2013)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 1: Soupapes de sûreté (ISO 4126- Teil 1: Sicherheitsventile (ISO 4126-1:2013)
1:2013)
This European Standard was approved by CEN on 28 December 2012.

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-CENELEC 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-CENELEC 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-1:2013: E
worldwide for CEN national Members.

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SIST EN ISO 4126-1:2013
EN ISO 4126-1:2013 (E)
Contents Page
Foreword .3
Annex ZA (informative) Relationship between this International Standard and the Essential
Requirements of EU Directive 97/23/EC (PED) .4

2

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SIST EN ISO 4126-1:2013
EN ISO 4126-1:2013 (E)
Foreword
This document (EN ISO 4126-1:2013) has been prepared by Technical Committee ISO/TC 185 "Safety
devices for protection against excessive pressure" in collaboration with Technical Committee CEN/TC 69
“Industrial valves” the secretariat of which is held by AFNOR.
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 January 2014, and conflicting national standards shall be withdrawn at
the latest by January 2014.
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 supersedes EN ISO 4126-1:2004.
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(s).
For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this document.
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 4126-1:2013 has been approved by CEN as EN ISO 4126-1:2013 without any modification.
3

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SIST EN ISO 4126-1:2013
EN ISO 4126-1:2013 (E)
Annex ZA
(informative)

Relationship between this International Standard and the
Essential Requirements of EU Directive 97/23/EC (PED)
By agreement between ISO and CEN, this CEN annex is included in the DIS and the FDIS but will not appear
in the published ISO standard.
This International Standard has been prepared under a mandate given to CEN by the European Commission
and the European Free Trade Association to provide one means of conforming to Essential Requirements of
the New Approach Directive 97/23/EC (PED).
Once this standard is cited in the Official Journal of the European Communities under that Directive and has
been implemented as a national standard in at least one Member State, compliance with the normative
clauses of this standard given in Table ZA.1 confers, within the limits of the scope of this standard, a
presumption of conformity with the corresponding Essential Requirements of that Directive and associated
EFTA regulations.
Table ZA.1 — Correspondence between this International Standard and Directive 97/23/EC (PED)
Sub-clauses of this International Essential Requirements of Directive 97/23/EC (PED)
Standard
Essential Requirements Annex I of PED
5,6,7,8,9 Safety accessories 2.11.1
5.1.5 Safety of operation 2.3
5.1.6 Drain and venting 2.5
6.3 Proof test 3.2.2
10 Marking and labelling 3.3

WARNING: Other requirements and other EU Directives may be applicable to the products falling within the
scope of this standard.

4

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SIST EN ISO 4126-1:2013
INTERNATIONAL ISO
STANDARD 4126-1
Third edition
2013-07-15
Safety devices for protection against
excessive pressure —
Part 1:
Safety valves
Dispositifs de sécurité pour protection contre les pressions excessives —
Partie 1: Soupapes de sûreté
Reference number
ISO 4126-1:2013(E)
©
ISO 2013

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2013 – All rights reserved

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 4
5 Design . 4
5.1 General . 4
5.2 Valve end connections . 5
5.3 Minimum requirements for springs . 5
5.4 Materials . 6
6 Production testing . 6
6.1 Purpose . 6
6.2 General . 6
6.3 Hydrostatic testing . 6
6.4 Pneumatic testing . 7
6.5 Adjustment of set or cold differential test pressure . 8
6.6 Seat leakage test. 8
7 Type testing. 8
7.1 General . 8
7.2 Tests to determine operating characteristics . 9
7.3 Tests to determine flow characteristics.11
7.4 Determination of the coefficient of discharge .12
7.5 Certification of coefficient of discharge .12
8 Determination of safety valve performance .13
9 Sizing of safety valves .13
10 Marking and sealing .13
10.1 Marking .13
10.2 Sealing of a safety valve .13
Bibliography .14
© ISO 2013 – All rights reserved iii

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
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.
ISO 4126-1 was prepared by Technical Committee ISO/TC 185, Safety devices for protection against
excessive pressure.
This third edition cancels and replaces the second edition (ISO 4126-1:2004), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 4126-1:2004/Cor.1:2007.
ISO 4126 consists of the following parts, under the general title Safety devices for protection against
excessive pressure:
— Part 1: Safety valves
— Part 2: Bursting disc safety devices
— Part 3: Safety valves and bursting disc safety devices in combination
— Part 4: Pilot operated safety valves
— Part 5: Controlled safety pressure relief systems (CSPRS)
— Part 6: Application, selection and installation of bursting disc safety devices
— Part 7: Common data
— Part 9: Application and installation of safety devices excluding stand-alone bursting disc safety devices
— Part 10: Sizing of safety valves for gas/liquid two-phase flow
1)
— Part 11: Performance testing
Part 7 contains data that is common to more than one of the parts of ISO 4126 to avoid unnecessary repetition.
1) Under preparation.
iv © ISO 2013 – All rights reserved

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SIST EN ISO 4126-1:2013
INTERNATIONAL STANDARD ISO 4126-1:2013(E)
Safety devices for protection against excessive pressure —
Part 1:
Safety valves
1 Scope
This part of ISO 4126 specifies general requirements for safety valves irrespective of the fluid for which
they are designed.
It is applicable to safety valves having a flow diameter of 4 mm and above which are for use at set
pressures of 0,1 bar gauge and above. No limitation is placed on temperature.
This is a product standard and is not applicable to applications of safety valves.
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.
ISO 4126-7:2013, Safety devices for protection against excessive pressure — Part 7: Common data
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
safety valve
valve which automatically, without the assistance of any energy other than that of the fluid concerned,
discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and
which is designed to re-close and prevent further flow of fluid after normal pressure conditions of
service have been restored
Note 1 to entry: The valve can be characterized either by pop action (rapid opening) or by opening in proportion
(not necessarily linear) to the increase in pressure over the set pressure.
3.2
direct loaded safety valve
safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by
a direct mechanical loading device such as a weight, lever and weight, or spring
3.3
assisted safety valve
safety valve which, by means of a powered assistance mechanism, may additionally be lifted at a pressure
lower than the set pressure and will, even in the event of failure of the assistance mechanism, comply
with all the requirements for safety valves given in ISO 4126
© ISO 2013 – All rights reserved 1

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

3.4
supplementary loaded safety valve
safety valve which has, until the pressure at the inlet to the safety valve reaches the set pressure, an
additional force which increases the sealing force
Note 1 to entry: This additional force (supplementary load), which may be provided by means of an extraneous
power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The
amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety
valve will attain its certified discharge capacity at a pressure not greater than 1,1 times the maximum allowable
pressure of the equipment to be protected.
Note 2 to entry: Other types of supplementary loaded safety devices are dealt with in ISO 4126-5.
3.5
set pressure
predetermined pressure at which a safety valve under operating conditions commences to open
Note 1 to entry: It is the gauge pressure measured at the valve inlet at which the pressure forces tending to open
the valve for the specific service conditions are in equilibrium with the forces retaining the valve disc on its seat.
3.6
maximum allowable pressure
PS
maximum pressure for which the protected equipment is designed
3.7
overpressure
pressure increase over the set pressure
Note 1 to entry: Overpressure is usually expressed as a percentage of the set pressure.
3.8
reseating pressure
value of the inlet static pressure at which the disc re-establishes contact with the seat or at which the
lift becomes zero
3.9
cold differential test pressure
inlet static pressure at which a safety valve is set to commence to open on the test bench
Note 1 to entry: This test pressure includes corrections for service conditions, e.g. back pressure and/or temperature.
3.10
relieving pressure
pressure used for the sizing of a safety valve which is greater than or equal to the set pressure plus
overpressure
3.11
back pressure
pressure that exists at the outlet of a safety valve as a result of the pressure in the discharge system
Note 1 to entry: The back pressure is the sum of the superimposed and built-up back pressures.
3.12
built-up back pressure
pressure existing at the outlet of a safety valve caused by flow through the valve and the discharge system
3.13
superimposed back pressure
pressure existing at the outlet of a safety valve at the time when the device is required to operate
Note 1 to entry: It is the result of pressure in the discharge system from other sources.
2 © ISO 2013 – All rights reserved

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

3.14
balanced bellows
device which minimizes the effect of back pressure on the set pressure and/or the operation of a safety valve
3.15
blowdown
difference between set and reseating pressures
Note 1 to entry: Blowdown is normally stated as a percentage of set pressure except for pressures of less than
3 bar when the blowdown is expressed in bar.
3.16
lift
actual travel of the valve disc away from the closed position
3.17
flow area
minimum cross-sectional flow area (but not the smallest area between disc and seat) between inlet and
seat which is used to calculate the theoretical flow capacity, with no deduction for any obstruction
3.18
flow diameter
diameter corresponding to the flow area
3.19
theoretical discharge capacity
calculated capacity expressed in mass or volumetric units of a theoretically perfect nozzle having a
cross-sectional flow area equal to the flow area of a safety valve
3.20
coefficient of discharge
value of actual flowing capacity (from tests) divided by the theoretical flowing capacity (from calculation)
3.21
certified (discharge) capacity
that portion of the measured capacity permitted to be used as a basis for the application of a safety valve
Note 1 to entry: It may, for example, equal the: a) measured flow rate times the derating factor; or b) theoretical
flow rate times the coefficient of discharge times the derating factor; or c) theoretical flow rate times the certified
de-rated coefficient of discharge.
3.22
DN (nominal size)
alphanumeric designation of size that is common for components used in a piping system, used for
reference purposes, comprising the letters DN followed by a dimensionless number having an indirect
correspondence to the physical size of the bore or outside diameter of the component end connection
Note 1 to entry: The dimensionless number does not represent a measurable value and is not used for
calculation purposes.
Note 2 to entry: Prefix DN usage is applicable to components bearing PN designations according to ISO 7268.
Note 3 to entry: Adapted from ISO 6708:1995, definition 2.1.
© ISO 2013 – All rights reserved 3

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

4 Symbols and units
Table 1 — Symbols and their descriptions
Symbol Description Unit
2
A Flow area of a safety valve (not smallest area between seat and disc) mm
a
K Coefficient of discharge —
d
a
K Certified de-rated coefficient of discharge (K × 0,9) —
dr d
n Number of tests —
2
q Theoretical specific discharge capacity kg/(h⋅mm )
m
2
q′ Specific discharge capacity determined by tests kg/(h⋅mm )
m
a
K and K are expressed as 0,xxx.
d dr
5 Design
5.1 General
5.1.1 The design shall incorporate guiding arrangements necessary to ensure consistent operation
and seat tightness.
5.1.2 The seat of a safety valve, other than when it is an integral part of the valve shell, shall be fastened
securely to prevent the seat becoming loose in service.
5.1.3 In the case of valves where the lift can be reduced to conform to the required discharge capacity,
restriction of the lift shall not interfere with the operation of the valve. The lift restricting device shall be
designed so that, if adjustable, the adjustable feature can be mechanically locked and access sealed. The
lift restricting device shall be installed and sealed in accordance with the design of the manufacturer.
Valve lift shall not be restricted to a value less than 30 % of unrestricted lift or 1 mm, whichever is the greater.
5.1.4 Means shall be provided to lock and/or to seal all external adjustments in such a manner so as to
prevent or reveal unauthorized adjustments of the safety valve.
5.1.5 Safety valves for toxic or flammable fluids shall be of the closed bonnet type to prevent leakage
to atmosphere, or if vented, it shall be disposed of in a safe place.
5.1.6 Provision shall be made to prevent liquid collecting on the discharge side of the safety valve shell.
5.1.7 The design stress of pressure-retaining shells shall not exceed that specified in the
appropriate standards.
NOTE For example, EN 12516 or ANSI/ASME B 16.34 may be used as reference.
5.1.8 The materials for adjacent sliding surfaces such as guide(s) and disc/disc holder/spindle shall be
selected to ensure corrosion resistance and to minimize wear and avoid galling.
5.1.9 The materials for the seat and disc of safety valves shall be selected to ensure resistance to
metallic bonding between these two surfaces in order to prevent an increase of set pressure, e.g. sticking
or cold working.
5.1.10 Sealing elements which may adversely affect the operating characteristics by frictional forces
are not permitted.
5.1.11 Easing gear shall be provided when specified.
5.1.12 Safety valves shall be constructed so that breakage of any part, or failure of any device, will not
obstruct free and full discharge through the valve.
4 © ISO 2013 – All rights reserved

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

5.2 Valve end connections
The inlet design of valve end connections, regardless of type, shall be such that the internal area of
the external pipe or stub connection at the safety valve inlet is at least equal to that of the valve inlet
connection [see Figure 1 a)].
The outlet design of valve end connections, regardless of type, shall be such that the internal area of
the external pipe connection at the safety valve outlet is at least equal to that of the valve outlet, except
those valves with female threaded outlet connections [see Figure 1 b)].
NOTE See Clause 7 regarding type testing.
a) Inlet
b) Outlet
Key
1 valve 3 unsatisfactory
2 satisfactory 4 required internal diameter of the safety valve for the
valve to function properly
a
If the nominal diameter of the pipe is not equal to the nominal diameter of the valve outlet, as shown, then a
suitable pipe shall be fitted during testing as specified in 7.1.5.
Figure 1 — Design of end connections
5.3 Minimum requirements for springs
Springs shall be in accordance with ISO 4126-7.
© ISO 2013 – All rights reserved 5

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

5.4 Materials
Only approved materials shall be used for pressure-retaining shells.
NOTE For example, EN 12516 or any other published national or international material standards (e.g. ASME,
ASTM, JIS, etc.) may be used as reference.
These materials and their temperature limitations shall be suitable for pressure-containing function.
6 Production testing
6.1 Purpose
The purpose of these tests is to ensure that all safety valves meet the requirements for which they have
been designed without exhibiting any form of leakage from pressure-retaining components or joints.
6.2 General
It is permissible to adopt an alternative test of equal validity (e.g. proof of design tests associated with
statistical sampling) to the hydrostatic test for valve shells with:
— threaded ends; and
— a maximum inlet diameter of 32 mm; and
— a ratio of bursting pressure to design pressure of at least 8; and
— a design pressure equal to or less than 40 bar; and
— for use with non-hazardous fluids;
and also for valves as above but with:
— a design pressure greater than 40 bar; and
— a ratio of bursting pressure to design pressure of at least 10; and
— material which is either wrought or forged.
All temporary pipes and connections and blanking devices shall be adequate to safely withstand the
test pressure.
Any temporary welded-on attachments shall be carefully removed and the resulting weld scars shall
be ground flush with the parent material. After grinding, all such scars shall be inspected by using
magnetic particle or fluid penetrant techniques.
6.3 Hydrostatic testing
6.3.1 Application
The portion of the valve from the inlet to the seat shall be tested to a pressure 1,5 times the manufacturer’s
stated maximum pressure for which the safety valve is designed.
The shell on the discharge side of the seat shall be tested to 1,5 times the manufacturer’s stated maximum
back pressure for which the valve is designed. This pressure can be lower than that given by the outlet
flange rating.
6 © ISO 2013 – All rights reserved

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SIST EN ISO 4126-1:2013
ISO 4126-1:2013(E)

6.3.2 Duration
The test pressure shall be applied and maintained at the required magnitude for a sufficient length of
tim
...

SLOVENSKI STANDARD
oSIST prEN ISO 4126-1:2010
01-marec-2010
Naprave za varovanje pred visokim tlakom - 1. del: Varnostni ventili (ISO/DIS 4126-
1:2009)
Safety devices for protection against excessive pressure - Part 1: Safety valves (ISO/DIS
4126-1:2009)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 1: Sicherheitsventile
(ISO/DIS 4126-1:2009)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 1:
Soupapes de sûreté (ISO/DIS 4126-1:2009)
Ta slovenski standard je istoveten z: prEN ISO 4126-1
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
oSIST prEN ISO 4126-1:2010 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 4126-1:2010

---------------------- Page: 2 ----------------------
oSIST prEN ISO 4126-1:2010


EUROPEAN STANDARD
DRAFT
prEN ISO 4126-1
NORME EUROPÉENNE

EUROPÄISCHE NORM

November 2009
ICS 13.240 Will supersede EN ISO 4126-1:2004
English Version
Safety devices for protection against excessive pressure - Part
1: Safety valves (ISO/DIS 4126-1:2009)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 1: Soupapes de sûreté (ISO/DIS 4126- Teil 1: Sicherheitsventile (ISO/DIS 4126-1:2009)
1:2009)
This draft European Standard is submitted to CEN members for parallel enquiry. It has been drawn up by the Technical Committee
CEN/TC 69.

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: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN ISO 4126-1:2009: E
worldwide for CEN national Members.

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oSIST prEN ISO 4126-1:2010
prEN ISO 4126-1:2009 (E)
Contents Page
Foreword .3

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oSIST prEN ISO 4126-1:2010
prEN ISO 4126-1:2009 (E)
Foreword
This document (prEN ISO 4126-1:2009) has been prepared by Technical Committee ISO/TC 185 "Safety
devices for protection against excessive pressure" in collaboration with Technical Committee CEN/TC 69
“Industrial valves” the secretariat of which is held by AFNOR.
This document is currently submitted to the parallel Enquiry.
This document will supersede EN ISO 4126-1:2004.
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(s).
Endorsement notice
The text of ISO/DIS 4126-1:2009 has been approved by CEN as a prEN ISO 4126-1:2009 without any
modification.

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oSIST prEN ISO 4126-1:2010

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oSIST prEN ISO 4126-1:2010
DRAFT INTERNATIONAL STANDARD ISO/DIS 4126-1
ISO/TC 185 Secretariat: ANSI
Voting begins on: Voting terminates on:
2009-11-05 2010-04-05
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION
Safety devices for protection against excessive pressure —
Part 1:
Safety valves
Dispositifs de sécurité pour protection contre les pressions excessives —
Partie 1: Soupapes de sûreté
(Revision of second edition of ISO 4126-1:2004 and of ISO 4126-1:2004/Cor.1:2007)
ICS 13.240

ISO/CEN PARALLEL PROCESSING
This draft has been developed within the International Organization for Standardization (ISO), and
processed under the ISO-lead mode of collaboration as defined in the Vienna Agreement.
This draft is hereby submitted to the ISO member bodies and to the CEN member bodies for a parallel
five-month enquiry.
Should this draft be accepted, a final draft, established on the basis of comments received, will be
submitted to a parallel two-month approval vote in ISO and formal vote in CEN.
To expedite distribution, this document is circulated as received from the committee secretariat.
ISO Central Secretariat work of editing and text composition will be undertaken at publication
stage.
Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du
secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au
Secrétariat central de l'ISO au stade de publication.
THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE
REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.
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.
©
International Organization for Standardization, 2009

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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
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©
ii ISO 2009 – All rights reserved

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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
Contents Page
Foreword.v
1 Scope.1
2 Normative references .1
3 Terms and definitions .2
4 Symbols and units.5
5 Design.5
5.1 General.5
5.2 Valve end connections.6
5.3 Minimum requirements for springs .8
5.4 Materials .8
6 Production testing .8
6.1 Purpose.8
6.2 General.8
6.3 Hydrostatic testing .9
6.3.1 Application .9
6.3.2 Duration .9
6.3.3 Acceptance criteria.9
6.3.4 Safety requirements .9
6.4 Pneumatic testing. 10
6.4.1 Application and duration of test. 10
6.4.2 Safety requirements . 11
6.5 Adjustment of set or cold differential test pressure . 11
6.6 Seat leakage test. 11
7 Type testing. 11
7.1 General. 11
7.1.1 Application . 11
7.1.2 Tests. 11
7.1.3 Objectives of tests. 12
7.1.4 Procedure for testing . 12
7.1.5 Results calculated from the tests . 12
7.1.6 Design changes . 12
7.2 Tests to determine operating characteristics. 12
7.2.1 General requirements. 12
7.2.2 Safety valve opening characteristics . 13
7.2.3 Test equipment . 13
7.2.4 Valves used in the test programme . 13
7.3 Tests to determine flow characteristics . 14
7.3.1 Test requirements. 14
7.3.2 Valves used in the test programme . 14
7.3.3 Test procedure. 14
7.3.4 Adjustment during test . 15
7.3.5 Records and test results. 15
7.3.6 Flow test equipment . 16
7.4 Determination of the coefficient of discharge . 16
7.5 Certification of coefficient of discharge. 16
8 Determination of safety valve performance.16
9 Sizing of safety valves . 16

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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
10 Marking and sealing.16
10.1 Marking on the shell of a safety valve.16
10.2 Marking on an identification plate .17
10.3 Sealing of a safety valve.17
Annex A (informative) Examples of sizing calculations for various fluids .18
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 97/23/EC (PED).19

©
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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 4126-4 was prepared by Technical Committee ISO/TC 185, Safety devices for protection against
excessive pressure.
This second edition cancels and replaces the first edition which has been technically revised.
ISO 4126 consists of the following parts, under the general title Safety devices for protection against
excessive pressure:
⎯ Part 1 : Safety valves
⎯ Part 2 : Bursting disc safety devices
⎯ Part 3 : Safety valves and bursting disc safety devices in combination
⎯ Part 4 : Pilot operated safety valves
⎯ Part 5 : Controlled safety pressure relief systems (CSPRS)
⎯ Part 6 : Application, selection and installation of bursting disc safety devices
⎯ Part 7 : Common data
⎯ Part 8 : (WI deleted for the moment)
⎯ Part 9 : Application and installation of safety devices excluding stand-alone bursting disc safety devices
⎯ Part 10 : Sizing of safety valves and connected inlet and outlet lines for gas/liquid two-phase flow (under
preparation)
⎯ Part 11: Performance Testing (under preparation)
Part 7 contains data that is common to more than one of the parts of this standard to avoid unnecessary
repetition.
Annex A is informative.
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oSIST prEN ISO 4126-1:2010

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oSIST prEN ISO 4126-1:2010
DRAFT INTERNATIONAL STANDARD ISO/DIS 4126-1

Safety devices for protection against excessive pressure —
Part 1:
Safety valves
1 Scope
This part of this Standard specifies general requirements for safety valves irrespective of the fluid for which they are
designed.
It is applicable to safety valves having a flow diameter of 4 mm and above which are for use at set pressures
of 0,1 bar gauge and above. No limitation is placed on temperature.
This is a product standard and is not concerned with applications for safety valves.
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.
ISO/DIS 4126-7:2009, Safety devices for protection against excessive pressure - Part 7 : Common data
EN ISO 6708, Pipework components - Definition and selection of DN (nominal size) (ISO 6708:1995)
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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
3 Terms and definitions
For the purposes of this Standard, the following terms and definitions apply.
3.1
safety valve
valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a
quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to
re-close and prevent further flow of fluid after normal pressure conditions of service have been restored
NOTE The valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily
linear) to the increase in pressure over the set pressure.
3.1.1
types of safety valve

3.1.1.1
direct loaded safety valve
safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct
mechanical loading device such as a weight, lever and weight, or a spring
3.1.1.2
assisted safety valve
safety valve which, by means of a powered assistance mechanism, may additionally be lifted at a pressure lower
than the set pressure and will, even in the event of failure of the assistance mechanism, comply with all the
requirements for safety valves given in this standard
3.1.1.3
supplementary loaded safety valve
safety valve which has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional
force which increases the sealing force
NOTE 1 This additional force (supplementary load), which may be provided by means of an extraneous power source, is
reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary
loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge
capacity at a pressure not greater than 1,1 times the maximum allowable pressure of the equipment to be protected.
NOTE 2 Other types of supplementary loaded safety devices are dealt with in Part 5 of this standard.
3.2
pressure
5
pressure unit used in this standard is the bar (1 bar = 10 Pa), quoted as gauge (relative to atmospheric pressure)
or absolute as appropriate
3.2.1
set pressure
predetermined pressure at which a safety valve under operating conditions commences to open
NOTE It is the gauge pressure measured at the valve inlet at which the pressure forces tending to open the valve for the
specific service conditions are in equilibrium with the forces retaining the valve disc on its seat.
3.2.2
maximum allowable pressure, PS
maximum pressure for which the protected equipment is designed
3.2.3
overpressure
pressure increase over the set pressure, usually expressed as a percentage of the set pressure.
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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
3.2.4
reseating pressure
value of the inlet static pressure at which the disc re-establishes contact with the seat or at which the lift becomes
zero
3.2.5
cold differential test pressure
inlet static pressure at which a safety valve is set to commence to open on the test bench
NOTE This test pressure includes corrections for service conditions, e.g. back pressure and/or temperature.
3.2.6
relieving pressure
pressure used for the sizing of a safety valve which is greater than or equal to the set pressure plus overpressure
3.2.7
Back pressure
Pressure that exists at the outlet of a safety valve as a result of the pressure in the discharge system
Note: The back pressure is the sum of the superimposed and built-up back pressures.
3.2.7.1
built-up back pressure
pressure existing at the outlet of a safety valve caused by flow through the valve and the discharge system
3.2.7.2
superimposed back pressure
pressure existing at the outlet of a safety valve at the time when the device is required to operate
NOTE It is the result of pressure in the discharge system from other sources.
3.3
balanced bellows
bellows device which minimises the effect of superimposed back pressure on the set pressure of a safety valve
3.4
blowdown
difference between set and reseating pressures, normally stated as a percentage of set pressure except for
pressures of less than 3 bar when the blowdown is expressed in bar
3.5
lift
actual travel of the valve disc away from the closed position
3.6
flow area
minimum cross-sectional flow area (but not the curtain area) between inlet and seat which is used to calculate the
theoretical flow capacity, with no deduction for any obstruction
NOTE The symbol is A.
3.7
flow diameter
diameter corresponding to the flow area
3.8
discharge capacity


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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
3.8.1
theoretical discharge capacity
calculated capacity expressed in mass or volumetric units of a theoretically perfect nozzle having a cross-sectional
flow area equal to the flow area of a safety valve
3.8.2
coefficient of discharge
value of actual flowing capacity (from tests) divided by the theoretical flowing capacity (from calculation)
3.8.3
certified (discharge) capacity
that portion of the measured capacity permitted to be used as a basis for the application of a safety valve
NOTE It may, for example, equal the:
a) measured flow rate times the derating factor ; or
b) theoretical flow rate times the coefficient of discharge times the derating factor ; or
c) theoretical flow rate times the certified derated coefficient of discharge.
3.9
DN (nominal size)
see EN ISO 6708
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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
4 Symbols and units
Table 1 — Symbols and their descriptions
Symbol Description Unit
2
A Flow area of a safety valve (not curtain area)
mm
Function of the isentropic exponent –
C
Theoretical capacity correction factor for subcritical flow –
K
b
a
Coefficient of discharge –
K
d
a
K Certified derated coefficient of discharge (K × 0,9) –
dr
d
Viscosity correction factor –
K
v
Isentropic exponent –
k
M Molar mass kg/kmol
Number of tests –
n
Relieving pressure bar (abs.)
p
o
Back pressure bar (abs.)
p
b
p Critical pressure bar (abs.)
c
Mass flow rate kg/h
Q
m
Theoretical specific discharge capacity 2
q
m
kg/(h⋅mm )
Specific discharge capacity determined by tests 2
q’
m
kg/(h⋅mm )
Universal gas constant –
R
Relieving temperature K
T
o
T Critical temperature K
c
Dynamic viscosity Pa·s
μ
3
Specific volume at actual relieving pressure and temperature
v
m /kg
Dryness fraction of wet steam at the valve inlet at actual relieving pressure –
x
b
and temperature
Z Compressibility factor at actual relieving pressure and temperature –

a
K and K are expressed as 0,xxx.
d dr
b
x is expressed as 0,xx.
5 Design
5.1 General
5.1.1 The design shall incorporate guiding arrangements necessary to ensure consistent operation and seat
tightness.
5.1.2 The seat of a safety valve, other than when it is an integral part of the valve shell, shall be fastened
securely to prevent the seat becoming loose in service.
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oSIST prEN ISO 4126-1:2010
ISO/DIS 4126-1
5.1.3 In the case of valves where the lift can be reduced to conform to the required discharge capacity,
restriction of the lift shall not interfere with the operation of the valve. The lift restricting device shall be
designed so that, if adjustable, the adjustable feature can be mechanically locked and access sealed. The lift
restricting device shall be installed and sealed by the valve manufacturer.
Valve lift shall not be restricted to a value less than 30 % of unrestricted lift or 1 mm whichever is the greater.
5.1.4 Means shall be provided to lock and/or to seal all external adjustments in such a manner so as to
prevent or reveal unauthorised adjustments of the safety valve.
5.1.5 Safety valves for toxic or flammable fluids shall be of the closed bonnet type to prevent leakage to
atmosphere or if vented it shall be disposed of to a safe place.
5.1.6 Provision shall be made to prevent liquid collecting on the discharge side of the safety valve shell.
5.1.7 The design stress of pressure retaining shells shall not exceed that specified in the appropriate
Standards.
NOTE As example, EN 12516 or ANSI/ASME B 16.34 may be used as reference
5.1.8 The materials for adjacent sliding surfaces such as guide(s) and disc/disc holder/spindle shall be
selected to ensure corrosion resistance and to minimise wear and avoid galling.
5.1.9 Seat and disc of safety valves shall be made of suitable material in order to avoid increasing of set
pressure, e.g. cold welding or sticking.
5.1.10 Sealing elements, which may adversely affect the operating characteristics by frictional forces, are not
permitted.
5.1.11 Easing gear shall be provided when specified.
5.1.12 Safety valves shall be so constructed that breakage of any part, or failure of any device, will not
obstruct free and full discha
...

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