Model "123" Back Pressure Relief Regulator,Graphite/Nbr Gaskets; 1/2" Size; Wcb Body & Spring Chamber; S40t Trim: 316SST With Tfe Seat,Fluorocarbon Elastomer (Fkm) Diaphragm; Opt-30: 150 Lb Raised Face Flanges; 40-100 PSIG Range Spring; Opt-25s: Screen For Spring Chamber Vent; Opt-40: Construction Per Nace Standard Mr0175