The Mechanical Handling and Storing of Material

2 l6 THE MECHANICAL HANDLING OF MATERIAL intact, either directly or indirectly; therefore a small volume of air admitted frequently will cause less strain on the exhauster and ensure more uniform working suction than will larger volumes of air admitted at longer intervals. Most modern pneumatic plants are now fitted with revolving air traps on the principle brought out by Haviland & Farmer, but much improved in detail. (See Figs. 291 to 293.) In the latest developments of the system by Mr Mitchell an improved Duckham type of trap has been introduced. I he Haviland & Farmer apparatus is provided, as already mentioned, with an exhaust pipe by means of which the air can be exhausted from the trap before it is filled with grain. A similar system of exhaust was in use in the early appliances of Duckham (see Fig. 283). It is difficult to say what effect the discharge of air from the Duckham pocket into the vacuum chamber has, but it would appear that the grain running into the pocket is met by the air trying to enter the vacuum chamber, which will not allow of the pocket being filled until the air pressure has been equalised. The grain suction pipe is illustrated in Figs. 294 to 296. Figs. 294, 295, and 296. Haviland & Farmer’s Grain Suction Pipe. 1 he pneumatic elevator on the blast system erected by Messrs Haviland & Farmer, which is at work at Sulina on the lower Danube, has now been reconstructed with the above-mentioned improvements, and is giving great satisfaction, as will be seen by the following figures. In 1901 the average quantity of grain per month passed through the machine was 19,197 tons. In 1902 the monthly average was 20,450 tons, giving an average annual tonnage for the two years of 237,000 tons. I he largest quantity dealt with in any one month was 38,978 tons, but the machine was capable of handling up to 50,000 tons per month. The result of a trial made to test the efficiency of the pneumatic grain elevator in the lower Danube in 1902 shows that with 375 indicated H.P. 160 tons of grain per hour were elevated to a height of 56 ft. The plant was reconstructed to the suction system in 1898 and further improved in 1903, after which 181 tons per hour were elevated to the same height with 350 indicated H.P., a much more satisfactory result. This shows conclusively that the principal imperfections of the original Duckham system were due to the leakage of the air trap and the imperfect exhauster, or rather the want of precautions to protect the exhauster from the injurious effects of the wheat dust.