Automatic Fill and Backflow Prevention Valve 3/4 Inch FNPT x 3/4 Inch FNPT

The Automatic Fill and Backflow Prevention Valve 3/4 Inch FNPT x 3/4 Inch FNPT (CAL-574151A) combines a hydronic pressure-reducing fill valve with an integrated backflow prevention section to maintain system static pressure while preventing reversal of heating-system water into the potable supply. The dual-chamber brass body uses standard 3/4 inch FNPT connections on both inlet and outlet, making it suitable for direct installation into residential and light commercial boiler make-up lines. Its internal regulating cartridge maintains the system’s cold-fill pressure, while the check-backflow section ensures compliance with plumbing codes for closed-loop heating applications. Designed for water or water-glycol media, the valve includes an internal strainer to reduce debris intrusion into the fill circuit. Although detailed face-to-face dimensions and flow coefficients are not publicly listed, the compact layout fits standard mechanical-room piping without requiring additional unions. For job fit, technicians must verify 3/4 inch FNPT piping, confirm the system’s required fill-pressure range, ensure correct flow orientation into the hydronic loop and confirm adequate clearance for servicing the strainer and regulator assembly. Installed properly, this valve delivers reliable make-up pressure control, safeguards the potable-water supply and supports long-term boiler system stability.