Watts 5 1/2″ relief valve 038880 this 1/2″ dual control regulator and relief valve is for use in commercial and residential hydronic heating systems to fill the boiler and piping system with water, and to maintain water pressure in the system at all times. It also provides make-up water to the system in the event of system leaks. It consists of an iron and bronze body construction with npt threaded inlet and outlet connections, an attached iron body, a tight seating check valve, diaphragm relief valve, purge lever for manual purging, and a stainless steel strainer. It has high capacity performance and a simplified servicing design. It is suitable for use in the boiler feed lines of hydronic heating systems. The maximum pressure is 100 psi (6.9 bar).