that other organizations of movable sprockets can be effectively utilized for example the length of the triangular courses of the conveyors in the respective sections as well as the extent of movement of the respective movable sprockets 52b therein need not be uniform instead these parameters can be designed to accommodate a particular product or range of products in the system fig3 and 4 illustrate schematically a simple organization of movable sprockets 52b suitable for practice of the invention in this organization the sprockets 52b which are driven by parallel chains 54 are mounted for rotation on an axle 56 the axle 56 contains at each opposite end a block bearing 58 that is adapted to undergo vertical sliding movement as represented by the arrows in fig4 within a guide structure 60 the block bearings 58 are adapted to be selectively moved in unison by lift motors 62 that connect to the respective block bearings 58 by means of connecting rods or cables 64 or the like which are capable of controllably raising or lowering the paired sprockets 52b as hereinafter described it should be appreciated that barring the use of means for adjusting chain length the guide structure will be formed as a large radius arcuate curve in order to maintain the tension in the respective chains 54 substantially constant schematically represented in fig6 and 7 is an alternative form of sprocket organization in which the movable sprockets 52b are supported by structural beam devices 66 of variable length to accommodate movement of the sprocket axles 56 the devices 66 each comprise an elongated block or beam 68 here shown as mounting an idler sprocket 52c and each pivotally attached at one end to the mount of the fixed sprocket 52a the sprocket 52b is rotatably attached to a.