BS EN ISO 4126-4:2004

BS EN ISO 4126-4:2004 Safety devices for protection against excessive pressure. Pilot operated safety valves

BS EN ISO 4126-4 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.

Contents of BS EN ISO 4126-4:

• Scope
• Normative references
• Terms and definitions
• Symbols and units
• Design
• General
• End connections
• Minimum requirements for springs
• Materials
• Production testing
• Purpose
• General
• Hydrostatic testing
• Pneumatic testing
• Adjustment of set or cold differential test pressure
• Seat leakage test
• Pressure seals
• Type testing
• General
• Tests to determine operating characteristics
• Tests to determine flow characteristics
• Determination of the coefficient of discharge
• Certification of coefficient of discharge
• Determination of pilot operated safety valve performance
• Determination of coefficient of discharge
• Critical and subcritical flow
• Discharge capacity at critical flow
• Discharge capacity for any gas at subcritical flow
• Discharge capacity for non-flashing liquid as the test medium in the turbulent zone where the
• Reynolds number Re is equal to or greater than 80 000
• Sizing of pilot operated safety valves
• General
• Valves for gas or vapour relief
• Calculation of capacity
• Marking and sealing
• Marking
• Sealing of a pilot operated safety valve
• Examples of capacity calculations for various media
• Capacity calculations for gaseous media at critical flow
• Capacity calculations for gaseous media at subcritical flow
• Capacity calculations for liquids
• Relationship between this European Standard and the Essential Requirements of EU Directive 97/23/EC (PED)