along the line marked b u2014 b this illustration shows how the cross section of the suction duct 21 increases from the tender side to the drive side this has the effect of ensuring that the speeds are more or less constant at all points over the sheet width as a result there are no local differences in air extraction and the risk of sheet breaks is reduced fig4 a and 4 b clearly show the route taken by the paper web 4 leading over the guide surface 18 of the separating box 9 at the inlet 18 u2032 and outlet 18 u2033 the web 4 enters and leaves at a tangent and the configuration of the inlet 18 u2032 and outlet 18 u2033 ensures that no more dust is generated by deflection of the web the air from the boundary layer is directed through the suction slot 19 into the collecting duct 21 the wall 20 of the chamber swivels about mounting 29 so that the suction slot 19 can be set and to allow the separating box 9 to be opened for cleaning purposes fig5 contains a view of the bottom separating box 10 again with the drive side of the paper machine on the left and the tender side on the right extraction takes place through a duct 26.