The drawing might require some explanations: imagine the EliTube cut along the line AA, as indicated in the small picture in the right hand bottom corner of Fig. 1. The arrows indicate the direction of the airflow as it enters the slot.

It is easy to imagine that the airflow tries to move the fibre strand towards the centre of the slot. The width of the fibre mass is reduced; a step in the correct direction. This effect is present regardless of the inclination of the slot. Adding a lid on top of the slot, as done by some systems, may enhance it. This effect merely pushes the fibres closer together without any impact of them being parallel.

2. The effect due to the inclination of the slot (Fig. 2)

FIG: 2

This is a dynamic effect. Assume fibre A has left the front nipping point. Its front portion is now on the lattice apron (perforated drum, or the like) and moving with the speed of the lattice apron. As its head crosses the upstream edge of the slot nothing at all happens.

It gets interesting when it tries to cross the downstream edge:

The suction applied to the slot does not allow the fibre to cross the edge. It is therefore forced to move along the edge. Now by the law of vectorial addition of speed (we are still well below Einsteins Theory of Relativity) the speed of the portion of fibres along the edge increases to

 

 

This increase in speed of the portion of fibre moving along the downstream edge causes the fibres to be gently stretched.