These mixing valves are among the most widely used in the world. Millions of them are in operation. Drive shaft and separation plates made of high-grade stainless steel; internal parts made from copper base alloy. Drive shaft and blade corrosion-resistant; no danger of seizing up. The 3-way mixing valve can only be installed in the vertical position (to avoid air pockets and dirt build-up). Exchange of shaft gasket (O-ring) possible without draining of heating system. All sizes of Viessmann 3-way mixing valves may be used with Viessmann mixing valve actuator of the same size. Three-Way Mixing Valve Model Size: 1". H = 7-3/4" / 195 mm, W = 5-3/4" / 146 mm. Max. operating pressure: 88 psig at 248ºF / 120ºC.