Since in a filling device the return gas pipe with its relative height position in the filling valve serves not only to precisely adjust the filling level in the container, but also plays an important role in flushing operations and/or in cleaning processes, and since bottlers often want to set different height positions of the return gas pipe, if possible without any external intervention, when changing between different container types, the well-known solution, i.e. to exchange return gas pipe end sections of different lengths, is too complicated and time-consuming, and a process has therefore been adopted in which the return gas pipe is adjusted by means of a positioning drive in a selective way and as required.
In the filling device known from DE 10 2005 031 319 A, the return gas pipe that is supported against rotation comprises an external thread meshing with an internal thread of a ring rotatably supported in the valve housing. A permanent magnet ring which electromagnetically cooperates through the wall of the valve housing with a stator that is stationarily arranged on the outside is positioned on the ring. Magnetic alternating fields that are rotating the ring and screw the return gas pipe in place are generated via the stator. Although this solution avoids any passages with seals (great constructional efforts, difficult cleaning operations, risk of leakage), noticeable electromagnetic losses and relatively great mechanical losses caused by the thread connection and the anti-rotation of the return gas pipe must certainly be accepted. The components for a precise mechanical conversion of rotational movements into linear movements lead not only to great mechanical losses, but, since they are exposed to the media in the filling device, they are objectionable in terms of hygiene and complicate the cleaning cycles.
In the filling device known from DE 198 55 975 C a permanent magnet ring is fixed to the return gas pipe, the ring electromagnetically cooperating through a chamber wall with a permanent magnet positioned outside the chamber. The outer permanent magnet is linearly adjusted in a mechanical way, dragging along the return gas pipe via the inner permanent magnet ring. However, this necessitates a mechanical passage that poses the known sealing and assembling problems. As an alternative, the return gas pipe can be directly coupled by mechanical actuation, but this requires a passage between zones of different pressures and different media. A further solution suggests an extended chamber leading to the outside for the return gas pipe, and a linearly adjustable permanent magnet that is positioned outside the extension and cooperates with the permanent magnet ring on the return gas pipe through the chamber wall. The precision that is achievable in adjusting operations is not always satisfactory because due to the transmission of the magnetic forces through a wall and because of the large gap the inner permanent magnet ring cannot follow the outer one in a very reliable way.