Fluidic devices built from suitable refractory materials can withstand the extreme conditions encountered in flows of molten metals - even those with a high melting point. This paper informs about the hydrodynamic aspects of a recent development of a fluidic controller keeping the metal gravity flow constant. The controller uses a narrow notch weir for generating the control signal and a fluidic vortex valve as the actuator. An unusual feature is the signal transfer between the two components performed also by a molten metal flow. It is even possible to amplify the signal using the liquid metal as the working medium in the amplifier.