Features Designed in collaboration with the Chlorine Institute, Inc. Provides reliability and safety beyond that possible with a conventional pressure relief valve. Inlet and outlet diaphragm seals effectively prevent the corrosion of internal working parts and the escape of fugitive emissions. Choice of 1½” and 4" (38 and 100 mm) inlet sizes. 1½” (38 mm) model equipped with a special Chlorine Institute-approved inlet flange and metal-to-metal seat. Optional 1½” 300 lb ANSI raised face flange adapter and elastomer O-ring seat available for exceptional tightness. 4" (100 mm) model standard with 4" 300 lb ANSI large tongue-faced inlet flange and metal seat Raised-face flange available as an option. Association of American Railroad Approval Nos. SRD-989034 and SRD-989035.