<p>A jet device for a machine mfg. partic. paper or cardboard web has a nozzle device for emitting a fluid jet under pressure directed onto the web or into the conveyor belt which carries the web. There is a changeover appts. to assist the adjustment of pressure at which the medium impinges either on the conveyor belt or the web. Also claimed is the application of a jet cutter, which separates a strip of material from web moved by the machine conveyor belt, as a device for cleaning the belt when the changeover appts. is supplied. Also claimed is the application of a device for cleaning the belt as a jet trimming cutter, esp. as the jet device when the changeover appts. is supplied.</p>
