Operates automatically off line pressure or independent pressure source. Heavy-duty, nylon-reinforced diaphragm isolates top chamber operating pressure from bottom chamber line pressure. Rectangular-shaped, soft seat seal provides drip-tight Class VI closure. Diaphragm assembly guided center and bottom. Throttling seat retainer for flow and pressure stability. Easily maintained without removal from the line. Diaphragm replaced without removing internal stem assembly. Replaceable seat ring. Alignment pins assure proper reassembly after maintenance. Center-tapped bonnet facilitates installation of position indicator or valve-actuated switches. Ductile iron and steel valves are epoxy-coated inside and out, for maximum corrosion protection. Valves are factory tested. Valves are serial numbered and registered to facilitate replacement parts and factory support.