Modern Gasworks Practice

THE MECHANICAL HANDLING OF MATERIALS 283 loaded with. coal, and the static load on each wheel. In addition, he should state the probable maximum load on any wheel due to abnormal circumstances—such as unevenness of the running track or excessive thnist caused. by stoppage in the retorts, etc. (see page 59). If the rail gauge is known the floor can then be designed. The majority of makers have a regulär form upon. which the necessary requirements for their machines are set out, but they can, of course, depart from some of them (within reasonable limits) withoiit afEecting the efficiency of the machiiie. In obtain-ing tenders the engineer should give the salient requirements demanded of the machiiie, such as the number of retorts to be chargcd. their size and a,rra,Tigement, and the method of coal-feeding proposed. So far as working capacity is concerned separate charging and discharging machines are, naturally, capable of dealing with a greater number of retorts than are the combined types. Machines operating from one side of the beuch, only are fast replacing those which operate simultaneously from both. sides. In the latter type the number of operators is doubled, and the Capital cost is increased by about 50 per cent. Where a chain or other working part enteis tlie retort, the retort must be kept a better shape, and usually requires scurfing more frequently. The working portions of the machine liable to breakage should be readily inter-changeable, and the engineer should know what spare parts he is expected to stock, as such, items have an important bearing upon the efficiency and cost of upkeep of the machine. The Arrol-Foulis Hydraulic Charger This charging machine is usually operated in conjmotion with a hydraulic discharger. Chargers are provided on each side of the retort beuch and deliver the coal from both ends up to the centre of the retort. Generally speaking, a system of overhead storage hoppers is provided in the retort house, and by means of suitable shoots the coal is led into the hopper carried on the front of the charger. The hopper on the machine is capable of holding sufficient coal to charge about fifteen retorts half-way through. The size of the hopper varies, however, with. the capacity of the retort beuch, and it may hold anything from 4 to 8 tons. Immediately beneath the hopper is fixed a revolving drum divided into compartments by radial partitions. By means of a ratchet and pawl arrangement a continuous rotary motion is imparted to this drum, and the extent to which it is turned regulates the amount of coal falling through, from the base of the hopper. On being discharged from th.e drum the coal falls into a special trough. which enters the retort for a few indies. A hydraulic pusher ram with. a plate attached to the free end then comes into operation and carries the coal charge into the retort. On the backward stroke of the pusher bar the coal drum is again revolved so that an.oth.er charge is ready to be pushed forward, oa the next outward stroke. By means of a special stopper bar the distance into the retort travelled by the ram is reduced by about 18 inches on each stroke, so that the coal is distributed comparatively evenly along the floor of the retort. For an ordinary medium charge seven strokes on each side of th.e beuch, are necessary to complete the work, but with. the modern heavy charge the stopper bars should pre-