SIST EN ISO 4126-5:2013

Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2013)

This part of ISO 4126 specifies the requirements for controlled safety pressure relief systems (CSPRS) irrespective of the fluid for which they are designed. It is applicable for main valves having a flow diameter of 4 mm and above which are for use at 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.

Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 5: Gesteuerte Sicherheitsventile (CSPRS) (ISO 4126-5:2013)

Diese Europäische Norm legt die Anforderungen an gesteuerte Sicherheitsventile (CSPRS) fest, unabhängig
von dem Medium, für das sie vorgesehen sind.
Die Norm gilt für Hauptventile mit einem engsten Strömungsdurchmesser von mindestens 6 mm und für
Drücke von 0,1 bar und höher. Hinsichtlich der Temperatur bestehen keine Einschränkungen.
Die vorliegende Norm ist eine Produktnorm und behandelt keine Anwendungsfälle.

Dispositifs de sécurité pour protection contre les pressions excessives - Partie 5: Dispositifs de sûreté à décharge contrôlés contre les surpressions (DSDCS) (ISO 4126-5:2013)

L'ISO 4126-5:2013 spécifie les exigences des dispositifs de sécurité piloté contre les surpressions (CSPRS), quel que soit le fluide pour lequel ils sont conçus.
Elle est applicable aux appareils de robinetterie principaux ayant un diamètre d'écoulement de 4 mm au moins qui sont utilisés à des pressions de 0,1 bar manométrique et au-dessus. Aucune limitation en température n'est spécifiée.
L'ISO 4126-5:2013 est une norme de produit et elle n'est pas applicable à la mise en ?uvre des CSPRS.

Naprave za varovanje pred visokim tlakom - 5. del: Krmiljeni varnostni sistemi za sproščanje tlaka (CSPRS) (ISO 4126-5:2013)

Ta del standarda ISO 4126 določa zahteve za nadzorovane varnostne sisteme za razbremenitev tlaka (CSPRS) ne glede na tekočino, za katero so oblikovani. Velja za glavne ventile s premerom pretoka 4 mm in več, ki se uporabljajo pri tlakih 0,1 bara in več. Temperatura ni omejena. To je standard izdelka in ne velja za uporabo.

General Information

• Status: Published
• Public Enquiry End Date: 24-Feb-2010
• Publication Date: 25-Jul-2013
• ICS: 13.240 - Protection against excessive pressure
• Technical Committee: IHPV - Hydraulics and pneumatics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 25-Jul-2013
• Due Date: 29-Sep-2013
• Completion Date: 26-Jul-2013
• Directive: 2014/68/EU - Directive 2014/68/EU of the European Parliament and of the Council of 15 May 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of pressure equipment
• Directive: 97/23/EC - Directive 97/23/EC of the European Parliament and of the Council of 29 May 1997 on the approximation of the laws of the Member States concerning pressure equipment
• Mandate: M/071 - Mandate to CEN for standardization in the field of Pressure equipment
• Ref Project: EN ISO 4126-5:2013 - Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2013)

Relations

• Replaces: SIST EN ISO 4126-5:2004/AC:2009 - Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2004/Cor 1:2006/Cor 2:2007)
• Effective Date: 01-Sep-2013
• Replaces: SIST EN ISO 4126-5:2004 - Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2004)
• Effective Date: 01-Sep-2013
• Amended By: SIST EN ISO 4126-5:2013/A1:2016 - Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2013/Amd 1:2016)
• Effective Date: 01-Sep-2016
• Replaces: SIST EN ISO 4126-5:2004 - Safety devices for protection against excessive pressure - Part 5: Controlled safety pressure relief systems (CSPRS) (ISO 4126-5:2004)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 4126-5:2013
01-september-2013
1DGRPHãþD
SIST EN ISO 4126-5:2004
SIST EN ISO 4126-5:2004/AC:2009
1DSUDYH]DYDURYDQMHSUHGYLVRNLPWODNRPGHO.UPLOMHQLYDUQRVWQLVLVWHPL]D
VSURãþDQMHWODND&6356,62
Safety devices for protection against excessive pressure - Part 5: Controlled safety
pressure relief systems (CSPRS) (ISO 4126-5:2013)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 5: Gesteuerte
Sicherheitsventile (CSPRS) (ISO 4126-5:2013)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 5:
Dispositifs de sûreté à décharge contrôlés contre les surpressions (DSDCS) (ISO 4126-
5:2013)
Ta slovenski standard je istoveten z: EN ISO 4126-5:2013
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
SIST EN ISO 4126-5:2013 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 4126-5:2013

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SIST EN ISO 4126-5:2013


EUROPEAN STANDARD
EN ISO 4126-5

NORME EUROPÉENNE

EUROPÄISCHE NORM
July 2013
ICS 13.240 Supersedes EN ISO 4126-5:2004
English Version
Safety devices for protection against excessive pressure - Part
5: Controlled safety pressure relief systems (CSPRS) (ISO
4126-5:2013)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 5: Dispositifs de sécurité asservis Teil 5: Gesteuerte Sicherheitsventile (CSPRS) (ISO 4126-
(CSPRS)) (ISO 4126-5:2013) 5:2013)
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 4126-5:2013: E
worldwide for CEN national Members.

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SIST EN ISO 4126-5:2013
EN ISO 4126-5:2013 (E)
Contents Page
Foreword .3
Annex ZA (informative) Relationship between this European Standard and the Essential
Requirements of EU Directive 97/23/EC (PED) .4

2

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SIST EN ISO 4126-5:2013
EN ISO 4126-5:2013 (E)
Foreword
This document (EN ISO 4126-5:2013) has been prepared by Technical Committee ISO/TC 185 "Safety
devices for protection against excessive pressure" in collaboration with the 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 4126-5:2004.
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.
For relationship with EU Directive, 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 4126-5:2013 has been approved by CEN as EN ISO 4126-5:2013 without any modification.
3

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SIST EN ISO 4126-5:2013
EN ISO 4126-5:2013 (E)
Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 97/23/EC (PED)
This European 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
5.1.6 Safety of operation 2.3
5.1.7 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 4126-5:2013
INTERNATIONAL ISO
STANDARD 4126-5
Second edition
2013-07-15
Safety devices for protection against
excessive pressure —
Part 5:
Controlled safety pressure relief
systems (CSPRS)
Dispositifs de sécurité pour protection contre les pressions excessives —
Partie 5: Dispositifs de sécurité asservis (CSPRS)
Reference number
ISO 4126-5:2013(E)
©
ISO 2013

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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(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 [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2013 – All rights reserved

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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 7
5 Design . 7
5.1 General . 7
5.2 Valve end connections . 9
5.3 Minimum requirements for springs .10
5.4 Materials .10
6 Production testing .10
6.1 Purpose .10
6.2 General .10
6.3 Hydrostatic testing .11
6.4 Pneumatic testing .11
6.5 Adjustment of set or cold differential test pressure .12
6.6 Seat leakage test.12
6.7 Pressure seals .12
7 Type testing.12
7.1 General .12
7.2 Tests to determine operating characteristics .14
7.3 Tests to determine flow characteristics.15
7.4 Determination of the coefficient of discharge .17
7.5 Certification of coefficient of discharge .17
7.6 Certification of CSPRS .17
8 Determination of CSPRS performance .17
9 Sizing of CSPRS .17
10 Marking and sealing .18
10.1 Marking .18
10.2 Sealing of a CSPRS .19
Bibliography .20
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(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 4126-5 was prepared by Technical Committee ISO/TC 185, Safety devices for protection against
excessive pressure.
This second edition cancels and replaces the first edition (ISO 4126-5:2004), which has been
technically revised. It also incorporates the Technical Corrigenda ISO 4126-5:2004/Cor 1:2006 and
ISO 4126-5:2004/Cor 2:2007.
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 development.
iv © ISO 2013 – All rights reserved

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SIST EN ISO 4126-5:2013
INTERNATIONAL STANDARD ISO 4126-5:2013(E)
Safety devices for protection against excessive pressure —
Part 5:
Controlled safety pressure relief systems (CSPRS)
1 Scope
This part of ISO 4126 specifies the requirements for controlled safety pressure relief systems (CSPRS)
irrespective of the fluid for which they are designed.
It is applicable for main valves having a flow diameter of 4 mm and above which are for use at 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.
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
controlled safety pressure relief system
CSPRS
system consisting of a main valve in combination with a control unit
Note 1 to entry: See Figure 1 for the components of a CSPRS.
Note 2 to entry: On reaching the set pressure, the operating forces on the main valve are by means of the control
unit automatically applied, released or so reduced that a main valve discharges a specified quantity of the fluid so
as to prevent the predetermined pressure being exceeded. The system is so designed that the main valve re-closes
and prevents a further flow of fluid after normal pressure conditions of service have been restored.
Note 3 to entry: Specific types of CSPRS are installed to protect the downstream system by preventing further
fluid input (safety shut-off valve). In this case the closing function shall meet the same requirements as the opening
function of the relief valve (see 5.1.5).
3.2
main valve
valve consisting of the parts of a CSPRS through which the discharge capacity is achieved, and the actuator
3.3
relieving principle
principle in which a main valve opens when the operating force is released or reduced, and in which the
main valve closes when the operating force is re-applied
Note 1 to entry: See Figure 2, Type 1.
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

3.4
loading principle
principle in which a main valve opens when the operating force is applied, and in which the main valve
closes when the operating force is removed
Note 1 to entry: See Figure 2, Type 2.
3.5
control unit
unit which establishes the opening and closing of the main valve
Note 1 to entry: The arrangement shall consist of redundant individual control paths in operation (see 5.1.13 and
5.1.15). The individual control path may consist of pressure tapping line, pressure sensor, sensing line, control
module and control line [see Figures 1 a), 1 b) and 1 c), principle for two control paths].
3.6
pressure tapping line
line to the pressure sensor
3.7
sensing line
line between the pressure sensor and control module
3.8
control line
line between the control module and the main valve
3.9
pressure sensor
comparator in which a predetermined adjustable value of pressure is compared with the actual
system pressure
Note 1 to entry: On reaching the predetermined pressure, a signal is transmitted to the control unit. The signal to
the control unit is removed when the system pressure has been lowered to a predetermined pressure.
3.10
control module
module which transforms the signal from the pressure sensor into a force to operate the actuator of
the main valve
3.11
closed circuit principle
principle characterized by the fact that on failure of the external control energy, the control unit effects
the loading or relief of the main valve
3.12
open circuit principle
principle characterized by the fact that on failure of the external control energy the control unit does not
change the loading or relief of the main valve
3.13
operating force
force which causes the main valve to operate
3.14
set pressure of a CSPRS
predetermined pressure at which a main valve disc under operating conditions commences to open
Note 1 to entry: It is the gauge pressure measured at the main valve inlet at which the pressure forces tending to
open the main valve for specified service conditions are in equilibrium with the forces retaining the main valve
disc on its seat.
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

3.15
maximum allowable pressure
PS
maximum pressure for which the protected equipment is designed
3.16
overpressure
pressure increase over the set pressure, usually expressed as a percentage of the set pressure
3.17
reseating pressure
value of the inlet static pressure at which the main valve disc re-establishes contact with the seat or at
which the lift becomes zero
3.18
cold differential test pressure
inlet static pressure at which the main 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.
3.19
relieving pressure
pressure used for the sizing of a CSPRS which is greater than or equal to the set pressure plus overpressure
3.20
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
3.21
opening sensing pressure
predetermined pressure which activates the pressure sensor
a) Two control lines, relieving principle
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

b) One control line, relieving principle
c) Two control lines, loading principle
Key
1 main valve 3.1 pressure tapping line
1.1 body 3.2 pressure sensor
1.1.1inlet port 3.3 sensing line
1.1.2outlet port 3.4 control module
1.2 actuator 4 control line
1.3 vent 5 check valve
2 control unit 6 protected system
3 individual control path
Figure 1 — Typical examples of redundancy for two individual control paths
4 © ISO 2013 – All rights reserved

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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

a) Type 1: Relieving principle
b) Type 2: Loading principle
Figure 2 — Operating principle of the main valve
3.22
closing sensing pressure
predetermined pressure which deactivates the pressure sensor
3.23
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.
3.24
built-up back pressure
pressure existing at the outlet of the main valve caused by flow through the main valve and the
discharge system
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

3.25
superimposed back pressure
pressure existing at the outlet of the main 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.
3.26
balanced bellows
bellows device which minimizes the effect of superimposed back pressure on the set pressure of a safety
valve
3.27
lift
actual travel of the main valve disc away from the closed position
3.28
flow area
minimum cross-sectional flow area (but not the smallest area between seat and disc) between inlet and
seat which is used to calculate the theoretical flow capacity, with no deduction for any obstruction
3.29
flow diameter
diameter corresponding to the flow area
3.30
theoretical discharge capacity
calculated capacity of a theoretically perfect nozzle having a cross-sectional flow area equal to the flow
area of the main valve
Note 1 to entry: Expressed in mass or volumetric units.
3.31
coefficient of discharge
value of actual flowing capacity (from tests) divided by the theoretical flowing capacity (from calculation)
3.32
certified (discharge) capacity
that portion of the measured capacity permitted to be used as a basis for the application of the CSPRS
Note 1 to entry: It may, for example, equal: a) the measured capacity times the de-rating factor; or b) the theoretical
capacity times the coefficient of discharge times the de-rating factor; or c) the theoretical capacity times the
certified de-rated coefficient of discharge.
3.33
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.
3.34
opening time
time interval for the main valve disc to move from the closed to the fully open position
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

3.35
reseating time
time interval for the main valve disc to move from the fully open to the closed position
3.36
opening dead time
time interval from the detection of the opening sensing pressure and the commencement of the opening
of the main valve
3.37
reseating dead time
time interval from the detection of the closing sensing pressure and the commencement of the closing
of the main valve
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 any valve in the system, other than where it is an integral part of the valve shell, shall
be fastened securely to prevent the seat becoming loose in service.
5.1.3 All external adjustments shall be locked and/or sealed in such a manner so as to prevent or
reveal unauthorized adjustments of the CSPRS.
5.1.4 In the case of main valves with restricted lift, the lift restricting device shall limit the main valve
lift but shall not otherwise interfere with the operation of the main valve. The lift restricting device shall
be designed so that, if adjustable, the adjustable feature can be mechanically locked and sealed. The lift
restricting device shall be installed and sealed in accordance with the design of the manufacturer.
The valve lift shall not be restricted to a value less than 30 % of the unrestricted lift or 1 mm,
whichever is greater.
5.1.5 For CSPRS working as safety shut-off valves it has to be assumed that the main valve cannot
be closed completely as a result of particles in the fluid. Upstream of the main valves, devices such as
perforated discs or strainers shall be installed. With the size of these bores or perforations, the leakage
rate of the main valve shall be determined.
5.1.6 Any CSPRS for toxic or flammable fluids shall be so designed to prevent leakage to atmosphere
or if vented it shall be disposed of in a safe place.
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SIST EN ISO 4126-5:2013
ISO 4126-5:2013(E)

5.1.7 The main valve shall be provided with a drain connection at the lowest point where liquid could
collect unless other provisions for draining are provided.
5.1.8 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.
5.1.9 The material of guiding surfaces shall be corrosion resistant and shall be selected to minimize
the possibility of galling or seizure.
5.1.10 Seat and disc of CSPRS shall be made of suitable material in order to avoid increasing set pressure,
e.g. cold welding or sticking.
5.1.11 The main valve opens without the assistance of any energy other than that of the fluid to be
relieved under the principle of 3.3 or 3.4 (see Figure 2). The d
...