553549A - Automatic Boiler Fill Valve with Pressure Indicator - 1/2" SWT x 1/2" MNPTCaleffi 553549A AutoFill Automatic Boiler Fill Valve, Pressure Indicator, 1 2" SWT x 1 2" MNPT The automatic filling valve is a device consisting of a pressure reducing valve with compensating seat, visual system pressure setting indicator, an inlet filter, anti scale internal parts, a shut off valve (round knob on bottom) and a check valve. It is installed on the water inlet piping in sealed heating systems, and its main function is to maintain the