1. In a conveying device, for pulverulent, granular, fibrous and fluid substances, the combination comprising a first flexible tube having a given inner radius open at its ends, means defining an inlet opening in said tube adjacent one end thereof, a flexible floating unattached core having a given outer radius disposed axially within the flexible tube and spaced from the internal wall of the tube so as to define therewith a longitudinal flow path of annular cross section, a spiral member disposed coaxially in the annular spacing between the core and the tube, and drive means for rotating said spiral member with respect to the tube and the flexible core to feed said substance toward means defining an outlet in said tube, the difference between the inner radius of said tube and the outer radius of said flexible core being slightly larger than the diameter of the wire which constitutes said spiral member, said drive means for rotating said spiral member being a variable speed means, and said conveying device constituting a volumetric device capable of transporting substances through an upwardly extending curvilinear path from said inlet opening to said outlet opening at a controlled rate.