In the G.S.34 valves, butterfly rotation is controlled by a hand-operated reducer which make it possible to fix the buttefly firmly in any position from 0¡ to 90¡. The reducer also makes adjustement easy even for the maximum flow diameters. These valves are made in n. diams. from 50 to 200 mm, and differ from the G.S.34 model in that they have a "Wafer" valve body for insertion between the flat flanges.