It is interesting to note that the German wording “Gesteuerte Sicherheitsventile” has no English equivalent “Controlled Safety Valves” in the technical sense. When translated into English, the German words “gesteuert” and “geregelt” both become “controlled”! Therefore the English expression “Controlled Safety Pressure Relief System” (CSPRS) was created in the European Standard EN ISO 4126-5 to prevent any confusion between “Controlled Safety Valves” and “Control Valves”!

For the past 40 years, CSPRS have been successfully used in Germany as safety devices for protection against excessive pressure especially in power plants both conventional and nuclear. The success of these valves rests on the fact that in contrast to directly loaded safety valves, they offer advantages regarding capacity, leak proof tightness up to actuation and testability. This inevitably results in a high degree of safety and simultaneously high availability.

By incorporating several functions, such as control and safety function in one evice, the economy is increased.

Since, on elaboration of the various European standards it was seen that different philosophies overlapped in the technical concepts of safety devices, this paper once again discusses the advantages. Typical application areas of CSPRS in power plants are presented and the advantages explained. The basic design and the different functional principles are also presented. Using an example, the necessity of recurrent tests with "diagnostic character" and the improvement of the easiness of testing are emphasized, which allows testing during plant operation without considerable operational disturbances.

Furthermore, a statistical evaluation of a large number of functional tests in power plants shows the advantages of CSPRS compared with direct loaded safety valves. Finally, the status of the acceptance of CSPRS in the European Standards is presented.

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