The Fast Fill Dual Control combines a Fast Fill boiler feed valve with an in-line pressure relief valve. Taco's Fast Fill boiler feed reducing valves are the perfect solution to low pressure problems in your hydronic system. The adjustable pressure range of the Fast Fill line makes it easy to optimize your system. Set your desired system pressure, and the 334-3 will maintain that pressure by adding water to your system automatically. An internal check prevents your system from emptying in the event of a pressure failure. By incorporating a pressure relief valve into the design the Dual Control not only manages the pressure between zones, it vents excess pressure as well. This keeps your system running safely and efficiently. Purging a system with Fast Fill valves is a breeze. The Fast Fill lever may be locked in the open position, overriding typical circulation processes.