To achieve maximum leak tightness between valve and pipeline, assembly of this butterfly valve is done by welding instead of bolting (Fig. 30). In general, the body length of this valve is similar to the double flanged version (Series 14 as per EN 558). However, it is easy to offer dif ferent body lengths, depending on customers' requirements. To prepare the valve for welding, the ends are designed with bevelled edges instead of flanges. Welding edges are preferred in appli cations where explosives, especially explosive gases, are pumped through pipelines.

Welding edges are preferred with metal sealing valves, as the components used for soft seats can be destroyed by heat from welding during installation.

Weld-end valves show one significant dis advantage, in that they are time- and labour consuming to dismantle from the pipeline in the case of failure, as the weld seam needs to be cut. In most cases, the valve will not be able to be used again.