A cylindrical distribution tube for use in an air sender distribution networ k comprises a horizontal section, and a ramp located in proximity to an output end of the horizontal section and sloping upward from a bottom of the horizontal section towards t he output end thereof. A vertical section extends upward from the output end of the horizontal section, and comprises a plurality of inwardly projecting dimples arranged around the circumference of the vertical section. A curved elbow connects the output en d of the horizontal section to a lower input end of the vertical section, and a curve d vane follows a center of the elbow anti divides the elbow substantially equally into upper and lower channels. The vane extends into the vertical section between the lowermost dimples. Capacity of the primary tube and the distribution network is increased and distribution uniformity of the network is improved.
