8900 Series Rev B Manway Emergency Relief Vents; Mates With API Flat Face Flange; 18" Size; 316 Stainless Steel Base; FEP Diaphragm; Model 8940 Hinged - Locking Design, Weight Loaded For Pressure,;Spring Loaded For Vacuum Relief; 0.2 - 1 Oz/In2 Vacuum Spring Range; Stainless Steel Weight Material