A Treatise On The Principles And Practice Of Dock Engineering

GRAIN ELEVATORS. 539 the bulwarks and hatchway coamings, and, at the same time, give the requisite inclination to the tip. Figs. 557 to 559 are illustrations of a hydraulic coal hoist and tip recently constructed at Dundee.* The hoist is designed to lift a 20-ton waggon through a height of 50 feet above the level of the jetty rails, and at the summit to tip it through an angle of 45 degrees. Owing to the difficulty of providing suitable founda- tions at a moderate cost, the structure having to stand in the river 120 feet beyond the line of quay, a suspended form of hoist has been adopted, instead of that in which the cradle is raised by direct-acting cylinders placed in a well below the surface of the quay. The hoist framing is of steel, braced and strutted, and securely bolted to the timber-work of the jetty. The cradle and tipping frame are lifted and lowered by four chains, two of which are for lifting and two for tipping. The lifting cylinder is fixed vertically against one side of the framing, and the tipping cylinder is fixed on the upper end of the lifting cylinder. Bach cylinder is fitted with a piunger, multiplying sheaves, guide bars, &c. The hoist is also furnished with a 2J-ton anti-breakage jcrane, having a lift of 55 feet. The structure is said to be the largest of its type. Owing to the dust arising from the shipment of coal, it is essential to locate tips at a safe distance from quays for the reception of cargo of a nature likely to be affected by it. Grain Elevators.—Appliances for dealing with cargoes of grain in bulk are necessarily very different from those employed in lifting packages and portable objects generally. In the case of a granulär substance it is clearly advantageous to provide some method of uninterrupted transmission, such as that afforded horizontally by endless bands in revolution, and vertically by a succession of buckets on a continuous chain. Pneumatic power, in the form of either suction or pressure through tubes, can also be employed to achieve the same result. When the quantity dealt with is small, or when it forms part of a miscellaneous cargo, intermittent discharge by means of grabs, worked by cranes, may suffice. The bucket system is in vogue at Liverpool and other places, and the rate of travelling reaches 100 feet per minute. An important drawback of the system is the limited range of self-feed for the buckets. lhey are only able to deal directly with the grain in the immediate vicinity of the hatch- way. That portion of it which lies under cover, it may be to the extent of a hundred feet or more, fore or aft, has to be trimmed in the direction of the buckets, generally by manual labour. The pneumatic system adopted at the Millwall Docks, London, and elsewhere, whilst entailing a greater consumption of coal than the bucket system, offers some advantages in other directions. The pneumatic tubes, being flexible, can be applied in any required position, and the cost of trimming is thereby saved, though at the same time the shifting of the * Buchanan on “ The Port of Dundee,” Min. Proc. Inst. O.E., vol. cxlix.