Modern Gasworks Practice

THE MECHANICAL HANDLING OF MATERIALS 333 being sufficient to move the switch to either position. The operating lever, or hånd wheel, makes exactly half a turn, and the switch, becomes locked for either direction by its connecting cranks coming exactly to “ deacl centre ” in each case. The overhead line switch, for changing the direction of the collecting trolley, is con-nected to this track-rail switch, and operates simultaneously with it. This form of track switch has proved highly successful, and a large nuniber of tli.em are in general use. It will be gathered from Kg. 216 that the telpher is designed to travel upon a single bulb rail, which is clipped to the top flange of the track gilder. The whole weight of the machine and the load carried by it is perfectly balanced abouttlie centre of the rail, and the wheel carriages are connected to the main frame by means of ball-bearing swivels. The construetion is such that a very high speed can be attained with negligible wear and tear, and with a very low power consumption. Curves of very small radii can be negotiated without any difficulty. One of the points of conflict in connection with. the telpher is that of top-rail versus bottom-flange support for the runners. There are very considerable differences in the two systems from an engineering point of view. Primarily, in the top-rail system the wheels are mounted above the track, with axles placed as beams supported at both ends and, therefore, in double shear; wliereas in the bottom-flange system the wheels must be mounted on cantilever pins in single shear, which is a serious-disadvantage when the heavy loads of the present day are taken into account. From the aspcct of wear and tear, moreover, the bearing surface is very mueh restricted in the bottom-flange system, whereas with a top-rail run there is no wear whatever on the track girder, which is essentially part of the structure. Again, very small radii may be negotiated with. the top-rail system; for instance, at the Southampton gasworks a 5-i-ton machine, carrying a gross load of 21 tons, traverses a curve of 9 feet 6 inches radius witli perfect ease. Machinery-Structure Eatio When considering maintenance and depreciation it is essential to bear in mind the very important, but often neglected, machinery-structure ratio. In other words, the structure forms by far the greater proportion of telpher plant, whereas with the conveyor the machinery, or moving portions, accounts for a much larger proportion of the total initial cost. The general custom with mechanical handling plant is to allow 10 per cent, for depreciation on moving parts and 2J to 3 per cent, on structures. In a telpher plant not more than one-third of the outlay is stink in. machinery, the structure accounting for two-thirds of the initial cost, wliereas with conveyor systems the converse is very nearly true. Moreover, the power absorbed in driving a conveyor is at least double that required to drive a mono-rail telpher of the same capacity per hour and where the material is carried through the same space. Telphers and Conveyors Compared The principal advantages associated with telpher handling are the amount of grouad which can be covered without excessive expenditure and the small amount