Tube with suction slots for a unit for condensing a bundle of textile fibres drafted in a spinning machine

A condensing unit for condensing a bundle of textile fibres coming from a drafting unit in a spinning station of a spinning machine, comprising:

• a fixed tube of substantially circular cross-section, which is common to several spinning stations located side by side, is connected to a suction source, and has, in each station, a suction slot located on the path of and along the direction of movement of the bundle of fibres,
• a plurality of annular or cylindrical filtering elements mounted so as to be freely rotatable on the fixed tube and each having a perforated portion which covers at least a corresponding slot, each filtering element being rotated about the fixed tube by a pressure roller which presses the bundle of fibres against the perforated portion of the filtering element,
• wherein the tube has, in each spinning station, a recess which extends along an arc of the circumference of the tube, the recess having a pair of axially spaced-apart radial surfaces adapted to cooperate with the filtering element in order to keep it in the correct axial position along the tube, with the perforated portion covering the slot.