BS EN ISO 4126-3:2020

What is ISO 4126-3 about?  

ISO 4126 is a series on safety devices for protection against excessive pressure. ISO 4126-3 details best practices for manufacturing and marking safety valves and similar pressure relief systems. 

ISO 4126 specifies the requirements for a product assembled from the in-series combination of safety valves or controlled safety pressure relief systems (CSPRS) according to ISO 4126-1, ISO  126-4 and ISO 4126-5, and bursting disc safety devices, according to ISO 4126-2, installed upstream of the valve within five pipe diameters of the valve inlet. 

ISO 4126-3 specifies the design, application, and marking requirements for such products, composed of the bursting disc safety device, a safety valve or CSPRS and a connecting pipe or spool piece. In addition, ISO 4126-3 gives a method for establishing the combination discharge factor used in sizing combinations. 

Who is ISO 4126-3 for? 

ISO 4126-3 on safety devices (safety valves and CSPRS) is useful for: 

• Valve manufacturers 
• Pressure vessel manufacturers 
• Design engineers 

Why should you use ISO 4126-3?  

A bursting disc is a non-reclosing pressure relief safety device that, in most cases, protects a pressure vessel, equipment or system from over pressurization or potentially damaging vacuum conditions. ISO 4126-3 discusses the safety valves and bursting disc in combination which can be used to protect the safety valve against corrosion, fouling or operating conditions that could affect the safety valve performance, to prevent leakage and to prevent total loss of contents from the protected equipment following the bursting of the bursting disc. 

Controlled safety pressure relief system CSPRS valves as mentioned in ISO 4126-3 are mainly used where conventional direct-loaded spring action valves cannot guarantee the opening and closing margins that certain specific conditions of the service demand. 

Using ISO 4126-3 you can design, mark, and apply safety valves and bursting discs on your pressure vessels in keeping with safety requirements. 

What’s changed since the last update?  

BS EN ISO 4126-3:2020 supersedes BS EN ISO 4126-3:2006. BS EN ISO 4126-3:2020 includes some technical changes with respect to BS EN ISO 4126-3:2006. These include: 

• Eliminated unnecessary references and definitions throughout the document 
• Clause 5: Inlet line and pressure drop requirements from prior 6.2 were moved to Clause 5 and a reference to ISO 4126-9 was also added 
• Clause 7: Deleted specific references to specific EN standards to refer to the applicable pressure vessel standard to reflect the global nature of this document 
• Clause 9: The restrictions for Fd values less than 0,97 were eliminated 
• Clause 12: Clarified the applicable minimum bursting pressure for which the Fd value can be used for sizes larger than those flow tested