14 because the band 24 is drawn the roller 46 are nonoperative during the horizontal movement along the upper moving path however the rollers 46 begin to operate as guide rollers when they run into the circular path surrounded by the arc shaped plates 50 thus holding the links 28 in the recesses of the chain wheels 36 the band therefore is smoothly guided downwards and after having reached the lower arc shaped guide rail 51 the guide rollers 46 begin to support the band along the further moving path when they run on the lower web of the arc shaped rail 51 and the lower horizontal guide rail 47 should the resistance of the pushed band portion increase no buckling can occur because of the upper webs of the circular guide rails 51 and the associated lower horizontal guide rails 47 the inner circular web of the lower arc shaped guide rail 51 in this embodiment can be omitted when the motor 42 is started in opposite direction the lower band portion is drawn and the upper portion is pushed in direction of the closing position of the band this portion is subjected to buckling that means the band tends to be lifted from the slide strips 18 this lifting however is limited by the guide rollers 46 which contact the upper guide flanges 62 of the guide rails 44 in the embodiment shown in fig5.