Overview
EN ISO 4126-3:2020 - Safety devices for protection against excessive pressure - Part 3: Safety valves and bursting disc safety devices in combination (ISO 4126-3:2020) specifies requirements for close‑coupled assemblies of bursting disc safety devices installed upstream of safety valves or CSPRS (Controlled Safety Pressure Relief Systems). The standard covers design, application, marking and a test method to determine the combination discharge capacity factor (Fd) used when sizing these combinations. It supersedes EN ISO 4126-3:2006 and is part of the ISO 4126 series on pressure‑relief safety devices.
Key topics and technical requirements
- Scope and definition: Applies to in‑series combinations where the bursting disc is installed within five pipe diameters upstream of the valve inlet.
- Design requirements: Requirements for the combined product (bursting disc, safety valve or CSPRS, and any connecting spool piece) to ensure reliable performance.
- Installation: Guidance on inlet line, pressure drop and close‑coupled installation; references ISO 4126‑9 for other arrangements.
- Performance and testing: Procedures and test rig requirements to determine the combination discharge capacity factor, Fd, and acceptance criteria for safety valve, bursting disc and combination tests.
- Derivation and certification of Fd: Methods for establishing and certifying the combination discharge capacity factor and guidance on alternatives to testing.
- Marking and documentation: Mandatory marking, identification and supplier documentation (including test certificates when certified Fd is used).
- Storage and transport: Preparation requirements for safe storage and shipment of combination devices.
- Regulatory alignment: Informative Annex ZA links this standard to essential requirements of EU Pressure Equipment Directive 2014/68/EU (PED) where applicable.
Practical applications and users
This standard is practical for:
- Valve and bursting disc manufacturers designing certified combination products.
- Pressure‑equipment and process engineers sizing relief systems for chemical, petrochemical, pharmaceutical and power industries.
- Safety engineers and plant operators specifying protection against excessive pressure and selecting close‑coupled solutions to prevent leakage, corrosion or loss of contents.
- Notified bodies, conformity assessors and certification organizations evaluating compliance with PED and international best practice.
Related standards
Keywords: EN ISO 4126-3:2020, safety valves, bursting disc, combination, discharge capacity factor, CSPRS, pressure relief, pressure equipment, PED.
