EN ISO 4126-3:2020 PDF

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

• ISO 4126‑1, ISO 4126‑2, ISO 4126‑4, ISO 4126‑5 (other parts of the ISO 4126 series)
• ISO 4126‑9 (other installation arrangements)
• EU Directive 2014/68/EU (Pressure Equipment Directive) - Annex ZA relationship provided in the standard

Keywords: EN ISO 4126-3:2020, safety valves, bursting disc, combination, discharge capacity factor, CSPRS, pressure relief, pressure equipment, PED.