The present invention relates to a method of manufacture of a channelling tube (10) with an insulating air gap (44) for transferring coolant from the outer platform to the inner platform of a hollow stator vane of a turbine. The purpose is to minimize heat transfer even at low flow rates of coolant in order to supply said coolant at the lowest possible temperature to the inner platform.
The tube is realized by tight rolling a flat metal sheet (16) in order to obtain a tight spiral defining a tube with an outer diameter d; said tube is then released so that it expands via a spring effect to an outer diameter D; the circumferential ends of the spiral are attached to the adjacent layer to define a central passage (42) for the coolant and the spiral gap (44) that creates insulation layer(s) around the central passage.