ISO 4126-4:2003 specifies general requirements for pilot operated safety valves, other than those covered in ISO 4126-1, 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. ISO 4126-4:2003 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.