Hoffman 401475, Model 508 Water Vent Valve, 1/8 NPT For automatic or manual venting systems. Ideal for use with Model 550 Air Chamber. Disc-type vent. Built-in check valve. Cartridge with discs can be replaced without draining the system. 1⁄8" NPT straight shank. Maximum water pressure 50 psig (3.5 bar). Maximum pressure 50 psig (3.5 bar).