The Mechanical Handling and Storing of Material

2o8 THE MECHANICAL HANDLING OF MATERIAL uneconomical. Within the last few years, however, certain modifications to the system have rendered it a little more economical. Whilst formerly pneumatic elevators and conveyors were only suitable for large installations, where such difficulties were of minor importance, to-day they may be employed for smaller installations also. With the building of larger ships, the need for speedy discharge, and the desire to be independent as far as possible of manual labour, have in the past decades been the means of introducing pneumatic elevators to a considerable extent, notwithstanding their heavy initial cost. The actual process of conveying by air is the same whether suction or blast is used, and it depends upon local conditions which of the two methods is the more suitable in each particular case. In the following descriptions pneumatic conveyors for grain are dealt with under the following three heads:—1. The Blast System ; 2. The Suction System; 3. The Combined Suction and Blast System. THE BLAST SYSTEM This is generally employed for greater distances of delivery than the suction system is suitable for, and also where it is more convenient to have the air compressor at the feeding end than to have the exhausters at the delivery end. The distance between the feeding and delivery points may be 1,000 ft., and in cases where the material has to be distributed to a number of points this form is very useful. To give a practical illustration of one way in which the blast system works, let us assume that it is required to load a ship from a lighter lying alongside. A barge called a machinery barge is fitted with a steam boiler, a set of air-compressing engines, and a quantity of flexible piping long enough to reach from any part of the lighter to the furthest corner of the ship to be loaded. To the inlet end of this piping where the grain enters, termed the nozzle, a smaller pipe is inserted. This pipe is in communication with the air compressor at the other end. A valve is fitted to it for admitting compressed air to the nozzle or shutting it off. When a lighter comes alongside to be discharged, a flexible pipe with its grain inlet nozzle is pushed into the grain, while the other end is led over the hatchway of the ship to be loaded. Upon the air compressor in the machinery barge being set to work, and the valve opened in the compressed air supply pipe, the air naturally rushes up the pipe and escapes at the other end which terminates over the batchway. If the hand be put over the nozzle where the compressed air enters, a strong suction will be felt, strong enough to draw in any granular material lying in close proximity to it. The action is similar to that of an injector, so that if the inlet nozzle be immersed in the grain to a depth of 12 to 18 in., the induced atmospheric air following the com- pressed air will take the grain around it to the mouth of the inlet nozzle, carry it up the pipe and deliver it into the hold of the vessel. The blast grain elevator brought out by the Atmospheric Grain Elevator Co., Ltd., under the Barclay & Walker patents, raises from 10 to 50 tons of grain per hour. It was erected for experimental purposes at the works of the Compressed Air Power Co., Ltd., Birmingham, with whom the firm made arrangements for the use of their compressed air. In the course of the experiment, six pipes were used for elevating maize to a hopper placed 40 ft. above the ground. In order to register the quantity of maize moved by means of the blast elevator during one hour, the hopper discharged the maize into a “ Chronos ” automatic weighing machine, which indicated the quantity handled. Of these six pipes, one was fitted up to raise 50 tons of material per hour to the bin, 40 ft. above the ground; two were made to elevate each 20 tons per hour to a hopper at