covered by components of the blow suction boxes 20 referring to fig2 6 the embodiments of the blow suction boxes 20 generally all comprise an upper wall 28 side walls 25 and 26 and vertical end walls 29a and 29b fig6 which have curved bottom edges 29v having a profile corresponding to the curve of the outer surface of shell 18 of deflection rolls 14 15 and 16 and spaced therefrom by a distance v if required sealing strips 29t acting on the outer surface of shell 18 may be provided in conjunction with the lower edges 29v in this case the perforations 19 of shell 18 all lie between the sealing strips and in any case are situated between the edges 29v referring now to the embodiment of fig2 the suction blow box 20 has an overpressure compartment 22 in which an overpressure p is maintained by means of a gas flow f o introduced through connector 21 ejection air flows f t and f l are directed through nozzle slits 32 and 34 of the suction blow box 20 the ejection gas flows f t and f l induce an underpressure in the gap spaces t t and t l defined by the walls 25 and 26 of blow suction box 20 and respective opposed incoming and outgoing straight runs of the web carrying wire 17 the underpressures in these gap spaces ensure that the web w is reliably held on the surface of the drying wire 17 on both the incoming and outgoing runs.