39 as shown in fig5 in cross section the air cylinder 32 is shown in which a piston 50 travels a cord 40 is attached to the piston and passes over pulley 38 to be fixed to an upright 44 on the carriage 16 likewise a cord 46 is attached to the piston 50 and passes over the pulley 39 and is finally attached to an upstanding member 48 on the carriage 16 the carriage 16 includes a platform 51 mounting wheels 52 which are adapted to travel in the rails 28 and 30 of the track 14 as shown in fig4 brackets 56 and 62 are fixed to the platform 51 and a sub frame 53 is pivotally mounted thereto a piston and cylinder arrangement 58 is pivotally mounted to a bracket 60 on the platform 51 at one end and to the sub frame 53 at the other end thereof a loading tray 54 is removably mounted on the sub frame 53 a bracket 63 made up of angle irons is fixed to the loading tray 54 and fits on the sub frame 53 when in place the sub frame 53 as shown in fig3 is fixed to a shaft 64 which in turn is journaled in the pivot brackets 56 and 62 the loading tray 54 is supplied with stacks of plastic bags b to be filled as previously mentioned the bags b are formed such that a valve opening b 1 as provided near one end thereof is spaced from.