Upper body and air-vent cap constructed of glass-filled nylon Internal and external bleed (flush mode) The Irritrol® 311 Series offers a comprehensive package of performance-enhancing features. Beginning with the reliability of a leak-proof, double-beaded, nylon-reinforced EPDM diaphragm, the strength of glass-filled nylon and the expanded range of a maximum working pressure rating of 150 psi, the 311 Series' list of features easily outdistances the competition. Compatibility with the OmniReg® modular pressure regulator make them the industry's only anti-siphon valves with a pressure regulation option. Additional features include an upgraded bonnet design, a self-cleaning metering system for dirty water applications and a captive plunger solenoid. Plus, the actuator module is removable as a single unit with the diaphragm and internal components held in place, which means no more lost diaphragm screws and springs during installation.