EN ISO 4126-4:2004

SLOVENSKI STANDARD
01-september-2004
Naprave za varovanje pred visokim tlakom - 4. del: Predkrmiljeni varnostni ventili
(ISO 4126-4:2004)
Safety devices for protection against excessive pressure - Part 4: Pilot operated safety
valves (ISO 4126-4:2004)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 4: Pilotgesteuerte
Sicherheitsventile (ISO 4126-4:2004)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 4:
Soupapes de sureté pilotées (ISO 4126-4:2004)
Ta slovenski standard je istoveten z: EN ISO 4126-4:2004
ICS:
13.240
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 4126-4
NORME EUROPÉENNE
EUROPÄISCHE NORM
February 2004
ICS 13.240
English version
Safety devices for protection against excessive pressure - Part
4: Pilot operated safety valves (ISO 4126-4:2004)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 4: Soupapes de sûreté pilotées (ISO Teil 4: Pilotgesteuerte Sicherheitsventile (ISO 4126-4:2004)
4126-4:2004)
This European Standard was approved by CEN on 16 May 2003.
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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-4:2004: E
worldwide for CEN national Members.

Contents
Page
1 Scope .4
2 Normative references .4
3 Terms and definitions.4
4 Symbols and units .9
5 Design .9
5.1 General.9
5.2 End connections .10
5.3 Minimum requirements for springs.12
5.4 Materials.12
6 Production testing .12
6.1 Purpose.12
6.2 General.12
6.3 Hydrostatic testing .12
6.4 Pneumatic testing .13
6.5 Adjustment of set or cold differential test pressure .14
6.6 Seat leakage test.14
6.7 Pressure seals.15
7 Type testing.15
7.1 General.15
7.2 Tests to determine operating characteristics.16
7.3 Tests to determine flow characteristics .18
7.4 Determination of the coefficient of discharge .19
7.5 Certification of coefficient of discharge .19
8 Determination of pilot operated safety valve performance .20
8.1 Determination of coefficient of discharge.20
8.2 Critical and subcritical flow .20
8.3 Discharge capacity at critical flow .20
8.4 Discharge capacity for any gas at subcritical flow .21
8.5 Discharge capacity for non-flashing liquid as the test medium in the turbulent zone where the
Reynolds number R is equal to or greater than 80 000 .21
e
9 Sizing of pilot operated safety valves.21
9.1 General.21
9.2 Valves for gas or vapour relief .21
9.3 Calculation of capacity.22
10 Marking and sealing .23
10.1 Marking .23
10.2 Sealing of a pilot operated safety valve .24
Annex A (informative) Examples of capacity calculations for various media .25
A.1 Capacity calculations for gaseous media at critical flow (see 9.3.3.1) .25
A.2 Capacity calculations for gaseous media at subcritical flow (see 9.3.3.2) .27
A.3 Capacity calculations for liquids (see 9.3.4) .28
Annex ZA (informative) Relationship between this European Standard and the Essential Requirements
of EU Directive 97/23/EC (PED).30
Foreword
This document (EN ISO 4126-4:2004) has been prepared by Technical Committee CEN/TC 69 “Industrial valves”,
the secretariat of which is held by AFNOR, in collaboration with Technical Committee ISO/TC 185 “Safety devices
for protection against excessive pressure”.
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 August 2004, and conflicting national standards shall be withdrawn at the latest by
August 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, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
This standard for safety devices for protection against excessive pressure consists of seven parts of which this is
Part 4. The various parts are:
 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 7 contains data that is common to more than one of the parts of this standard to avoid unnecessary repetition.
Annex A is informative.
1 Scope
This part of this European Standard specifies general requirements for pilot operated safety valves, other than
those covered in Part 1, irrespective of the fluid for which they are designed. In all cases, the operation is carried
out by the fluid in the system to be protected.
It is applicable to pilot operated safety valves having a valve flow diameter of 6 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 it is not concerned with applications for pilot operated safety valves.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN 1092-1, Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 1: Steel flanges.
EN 1092-2, Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 2: Cast iron flanges.
EN 1092-3 , Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 3: Copper alloy and composite flanges.
prEN 1759-1, Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories, Class
designated – Part 1: Steel flanges NPS1/2 to 24.
EN 12516-3, Valves – Shell design strength – Part 3: Experimental method.
EN 12627, Industrial Valves – Butt welding ends for steel valves.
EN 12760, Valves – Socket welding ends for steel valves.
EN ISO 6708, Pipework components – Definition and selection of DN (nominal size) (ISO 6708:1995).
ISO 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances and
designation.
ASME B1.20.1, NPT threads.
3 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1
pilot operated safety valve
self actuated device comprising a valve and an attached pilot
NOTE The pilot responds to the pressure of the fluid without any other energy than the fluid itself and controls the
operation of the valve. The valve opens when the fluid pressure that keeps it closed is removed or reduced. The valve re-closes
when the pressure is re-applied.
3.1.1
types of pilot
3.1.1.1
flowing pilot
pilot which discharges the fluid throughout the relieving cycle of the pilot operated safety valve
3.1.1.2
non-flowing pilot
pilot in which the fluid flows only during the opening and/or closing of the pilot operated safety valve
3.1.2
types of action of the pilot operated safety valve
3.1.2.1
ON/OFF
action characterised by stable operation resulting in fully open or fully closed main valve position
3.1.2.2
modulating
action characterised by a gradual opening and closing of the disc of the main valve which is a function of the
pressure, proportional but not necessarily linear
3.2
list of main components
see Figure 1
Key
1 Equipment to be protected 9 Disc
2 Main valve 10 Seat
3 Pilot valve 11 Body
4 Sensing line 12 Inlet
5 Loading/unloading line 13 Outlet
6 Pressure chamber 14 Pilot outlet
7 Cover 15 Connection of the sensing line : see the following note
8 Guide
NOTE The sensing line from the pilot can be either connect
...