sliding guide bore 13 of the mounting 9 the magnet body can be embodied as separate part from a ferromagnetic material or consist of the blow nozzle consisting at least in sections of a ferromagnetic material or designed as permanent magnet in the represented embodiment two magnet coils 11 a 11 b superimposed in the direction h are provided the magnet coil 11 a being used for lifting and the magnet coil 11 b located thereunder being used for lowering the blow nozzle 2 in a movement over a single stroke h 1 further magnet coils can be provided to realize deviating lengths of stroke for example a third magnet coil can be provided above the first magnet coil 11 a which realizes a second longer stroke h 2 the lower magnet coil 11 b causing the return into the lowered position drawn in fig1 for both strokes all magnet coils 11 are supplied via a power source 14 and provided with a non depicted control means which controls the stroke and the application of the magnet coil required in each case furthermore the force of pressure between the two openings 5 6 can also be caused electromagnetically which can be realized for example by an additional coil in the region of the openings 5 6 or by the lower coil 11 b furthermore a non depicted spring can be provided which acts.