Model "2171" Back Pressure Relief Regulator, Tfe Gasket/O-Ring; 1/2" Size, Angle Design (Side Inlet(S) - Bottom Outlet); 316l SST Body & Cf3m SST Spring Chamber; S1 Trim: 316l SST Metal Seat,302SST Diaphragm; Npt Screwed; 270-400 PSIG Range Spring (Includes Opt-80: High Inlet Pressure;Construction); Opt-25: 1/8" Npt Spring Chamber Vent Tap