Model "123" Back Pressure Relief Regulator,Graphite/Nbr Gaskets; 1-1/2" Size; Wcb Body & Spring Chamber; S1 Trim: 316SST Metal Seat,302SST Diaphragm; Opt-30: 300 Lb Raised Face Flanges; 180-350 PSIG Range Spring; With Special: 3/8" Npt Spring Chamber Vent Tap