The Mechanical Handling and Storing of Material

THE HANDLING OF MATERIAL BY PNEUMATIC MEANS 219 at the “canister.” These pipes are made of conical steel plate rings 6 in. long over- lapping each other, the whole being taped together with flax webbing and encased in a jacket made of leather, or of canvas impregnated with rubber. The pipe is made up in lengths of 10 ft., which are coupled together with bolt couplings having internal rubber washers to keep them air-tight. Steel taper pieces are used to 1 educe the diametei to 6 in. at the lower end where connection is made with the nozzles. I he steel rings resist the wear by friction of the grain and the enveloping hose makes the joints of the cones air-tight. The pipe is supported by chains slung from derricks and is so flexible that a 10-foot length may be bent to a quarter circle. The nozzles are of steel of 6 in. internal diameter and about 2 ft. long ; the adjust- able sleeve outside allows an air space of 1 in. all round. I his sleeve must be adjusted to give the necessary supply of air. This is a most important factor, as the vacuum obtainable is directly controlled thereby. The range of the sleeve may be taken as 2 in. for extreme positions. With good oats it may be raised an inch and a half above the nozzle but with sluggish wheat it will have to be brought down half an inch below it. By lowering the sleeve more air is admitted; this is required for higher lifts or when the pipes are much curved for getting under the coamings. There are two varieties of nozzle used, “straight” and “camel back,” the latter type being kept for working under coamings or in places inaccessible to the straight nozzle. From the canister, where the air and grain are separated, the latter passes through the tipper into a weighing hopper, where it is drawn oft by means of a slide valve into the weighing machine. That portion of grain intended for shore goes through weighing machines and thence by hopper to a band conveyor on the bridge spanning the 50 ft. to the quay. The remainder is weighed and passed direct into craft alongside through steel.spouts, being either sacked on platforms, slung from the “dolphin, or it may be moved in bulk. Before finding its way to ths atmosphere the exhaust air from the pumps is passed through a “ stive-room ” or settling chamber of 3,000 cub. ft. capacity ; these stive-rooms form the lower part of the towers. Here any dust which may have passed through the pumps impinges on baffle plates, is collected by a mechanical scraper gear, and is led eventually to the canister through a by-pass, being again incorporated with the grain to maintain its weight. There are two floating elevators with a collective output of 250 tons per hour. The machinery is of the type already described, but is placed on floating steel tanks or barges, which are capable of being navigated in the dock. The larger vessel known as “ Mark Lane No. 3 ” has two towers and is 90 ft. long, a smaller “ Mark Lane No. 2 has one tower and is 65 ft. long, the beam in each case being 24 ft., and the draught 10 ft. Lhe discharge is direct to barge only, from which the grain, if required for housing, is trans- ferred to the travelling bins by means of grabs. What appears to be an important feature in this new installation at the Millwall Docks is the tapering pipes. Mr Magnus Mowat, M.Inst.C.E., has carried out a series of experiments to determine the efficiency of these tapering pipes as compared with the 6-in. cylindrical pipes of the earlier plants, and the tests have shown that on the same receiver two of the taper pipes dealt with more grain than three of the 6-in. cylindrical pipes working under similar conditions. He also found that the velocity of the air in the pipes is approximately 100 to 150 ft. per second, and that the mixture of grain and air might be averaged at 1 to 50. Although the latest installation at the Millwall Docks provides 3 I.H.P. per ton of grain lifted, Mr Magnus Mowat states that actually only 2'5 H.P. is required per ton per