The so-called wafer type is a butterfly valve which is clamped between two flanges of the pipeline by force, without being bolted directly to the pipe line. The body of such a valve is supplied either with centring aids or without centringaids. The wafer design saves weight and costs, compared to lug-type butterfly valves. De pending on the manufacturer, it can be delivered with centring aids to make assembly in the pipe line casier. Centring aids align the valve in a con centric way in the pipeline on the one hand, and relieve the assembly worker from the weight of the valve on the other hand. In Europe, the body length of these butterfly valves is defined by the standard DIN EN 558. Here, two popular dimensions have proven to be successful: Series 20 and 25. In some cases, Series 16 is used (longer than Series 20 and 25). In other countries, body lengths based on ASME-standards are common, but they are connected to a pressure rating, for example Class 150 and Class 300, which corres ponds to 19 bar and 51 bar (275 and 739 PSI), respectively.