NEN EN ISO 4126-4 : 2013

Foreword
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and units
5 Design
   5.1 General
   5.2 End connections
   5.3 Minimum requirements for springs
   5.4 Materials
6 Production testing
   6.1 Purpose
   6.2 General
   6.3 Hydrostatic testing
   6.4 Pneumatic testing
   6.5 Adjustment of set or cold differential test pressure
   6.6 Seat leakage test
   6.7 Pressure seals
7 Type testing
   7.1 General
   7.2 Tests to determine operating characteristics
   7.3 Tests to determine flow characteristics
   7.4 Determination of the coefficient of discharge
   7.5 Certification of coefficient of discharge
8 Determination of pilot operated safety valve performance
   8.1 Determination of coefficient of discharge
   8.2 Critical and subcritical flow
   8.3 Discharge capacity at critical flow
   8.4 Discharge capacity for any gas at subcritical flow
   8.5 Discharge capacity for non-flashing liquid as the
        test medium in the turbulent zone where the Reynolds
        number R[e] is equal to or greater than 80000
9 Sizing of pilot operated safety valves
   9.1 General
   9.2 Valves for gas or vapour relief
   9.3 Calculation of capacity
10 Marking and sealing
   10.1 Marking
   10.2 Sealing of a pilot operated safety valve
Annex A (informative) Examples of capacity calculations for
        various media
   A.1 Capacity calculations for gaseous media at critical flow
   A.2 Capacity calculations for gaseous media at subcritical flow
   A.3 Capacity calculations for liquids
Annex ZA (informative) Relationship between this European
         Standard and the Essential Requirements of EU
         Directive 97/23/EC (PED)

Defines general requirements for pilot operated safety valves, irrespective of the fluid for which they are designed.