What is ISO 4126-5 - Safety devices for protection against excessive pressure about?
ISO 4126 is a series on safety devices for protection against excessive pressure. A pressure relief device is a general term for a device designed to prevent pressure or vacuum from exceeding a predetermined value in a pressure vessel by the transfer of fluid during an emergency or abnormal pressure conditions. ISO 4126-5 specifies the requirements for controlled safety pressure relief systems (CSPRS) irrespective of the fluid for which they are designed.
ISO 4126-5 is applicable for main valves having a flow diameter of 4 mm and above which are for use at pressures of 0,1 bar gauge and above. No limitation is placed on temperature. ISO 4126-5 specifies Controlled safety pressure relief systems which is a type of safety system used to control or limit the pressure in a system.
Who is ISO 4126-5 - Safety devices for protection against excessive pressure for?
ISO 4126-5 on safety devices for protection against excessive pressure is useful for:
- Industries dealing using high-pressure machinery
- Pressure valves manufacturers
- Design engineers
- Quality control personnel
- Research and development facilities
Why should you use ISO 4126-5 - Safety devices for protection against excessive pressure?
The controlled safety pressure relief system is a special type of actuated SRV. ISO 4126-5 provides detailed information on a controlled safety pressure relief system. A controlled safety pressure relief system is defined as, on reaching the set pressure, the operating forces on the main valve are by means of the control unit automatically applied, released, or so reduced that the main valve discharges a specified quantity of the fluid to prevent the predetermined pressure being exceeded. The system is so designed that the main valve re-closes and prevents a further flow of fluid after normal pressure conditions of service have been restored.
A controlled safety pressure relief system is, in fact, a spring-operated SRV that can operate as stand-alone but in normal operations is controlled by an actuator (usually pneumatic or hydraulic) and which opens upon the signal of an instrumentation loop. Due to the additional force on the spring, a more accurate set pressure can be obtained, therefore allowing the user to operate at higher process pressures. 
The purpose of these tests as mentioned in ISO 4126-5 is to ensure that each controlled safety pressure relief system meets the requirement for which it has been designed without exhibiting any form of leakage of pressure-retaining components or joints. Using ISO 4126-5 you can specifies the requirements for controlled safety pressure relief systems (CSPRS) irrespective of the fluid for which they are designed.
