All characteristics and technical features of the stainless steel versions also apply to the series 684 made of corrosion-resistant gunmetal. The fully relieved valves which therefore even out inlet pressure variations are available with and without secondary venting and each in a diaphragm or a piston version. Pressure adjustment is carried out without tools via the ergonomically formed hand-wheel. The extremely small pressure loss in the pressure adjusting area leads to these high-performance pressure reducing valves having almost no competition.