Model 1049 Rev A Pilot Operated Vent Valve; Carbon Steel Body; 3" Inlet X 4" Outlet, Mates With ASME 150 RF Flanged End Connections; Fluorocarbon Elastomer (FKM) Soft Seats; Option 1: Internal Sensing With Pilot Exhaust Tubed To Main Valve Outlet; Fluorocarbon Elastomer (FKM) Actuator Diaphragm; 1.2 - 4.0" wc Low Pressure Range With Special External Air Assist Pilot