Function The Caleffi 573002A automatic filling valve is a device consisting of a pressure reducing valve with compensating seat, visual system pressure setting indicator, an inlet fi lter, 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 pressure of the system at a set value, automatically fi lling up with water as required. The valve is pre-adjustable, meaning it can be set to the desired pressure value before the system charging phase. After installation, during the fi lling or topping-off phase, the water feed will stop when the set pressure is reached. This valve fi lls 50% faster than other valves. There are no levers to fl ip or valve to close.