unit 80 which communicates with a sensor 90 for example for measuring the sealing gap u a fan device 60 is further arranged in the connecting line 40 which is used to produce the flow in the tubing system or at least to support the same the fan device 60 can also be controlled by the control unit 80 moreover a filter unit 50 is arranged upstream of the heating device 70 which especially removes solids from the control medium or the air the air heated by means of the heating device 70 and or the fan device 60 is finally discharged via the outlet 192 after having flowed along the tension rod 14 over virtually its entire length and is preferably supplied to the gas volume flow 4 to be heated not shown the rod bodies 13 and 14 can be subjected to different temperatures with the illustrated arrangement this leads to a good controllability furthermore it is possible to provide an indirect control of a sealing gap depending on the temperature of the gas volume flows and a partial volume flow which is possibly branched off from the same it thus offers the advantage that a flow along the rod bodies 13 and 14 specifically predetermined by the chambers 171 and 172 can be produced so that a defined heat transfer to the rod bodies 13 and 14 is ensured it is thus also possible to easily determine the dependence on the changes in axial length or the flow volume of the air or the control medium and to set the sealing gap u on.