At the development of the new series of API- Safety Relief Valves extensive investigations of the fluid-flow were done with modern measurement technology for the recording of the function, the discharge capacity and the flow force. A new method of „Flowforce - Characteristic - Measurement" gives the possibility of an extensive review of the quality of the shape of all parts in the flowing area and the information of possible parts-optimizing. Due to the high productive power of the Bopp & Reuther test facility it was possible to do the verifications of the required characteristics for a larger field of pressure and size much larger than needed for an ASME - certification. In addition to these measurements special flow calculations give the knowledge about local fluid dynamics and therefore the possibility to optimize with high accuracy the parts in the flowing area. The result is the new series of API - Safety Relief Valves with ASME- and TÜV certification which gives a lot of advantages for the users.