Plugging indicator

A plugging indicator comprises an economizer having concentric outer and inner pipes one ends of which are connected to a main conduit through which liquid metal passes, an electromagnetic pump mounted on the outer pipe for branching the liquid metal into the outer pipe, a device for measuring flow quantity of the liquid metal passing through the outer pipe, and cooling means mounted on the outer pipe. The inner pipe is provided with two openings as a plugging orifice and a by-pass orifice to deposit impurities contained in the liquid metal. The plugging indicator further comprises a thermometer for measuring temperature at the plugging orifice, a blower for supplying cooling air to the cooling means, and a device for controlling the blower in response to the flow quantity at the flow quantity measuring device and the temperature at the plugging orifice.