The Mechanical Handling and Storing of Material

THE HANDLING OF MATERIAL BY PNEUMATIC MEANS 215 in turn comes under the aperture in the bottom of the vacuum tank, the air is previously withdrawn from them by a pipe w, the valve w' being open. When a winnowing effect is desired for the purpose of drawing the dust from the cargo, the valve g' in the suction pipe connected to the gauze filter is shut, and the valve g" on the pipe g'"> communicating also with the vacuum pipe and vacuum tank, is opened. This allows the dust and husk laden air to be withdrawn and deposited in the dust collector. The valve w' is also partly or quite shut, which causes the air contained in the pockets to blow through the grain as it falls into them. By this arrangement the grain cargo can be delivered, either with a minimum loss of weight, or, on the other hand, the dust, husks, etc., may be extracted to clean the grain, should this be essential. x represents the water dust collector, the under part x' of which is filled with water, sealing the bottom of the vacuum chamber x"Above this, and communicating with the exhausters D, D, is a further pipe H. The pipe G conducts the dust-laden air from the overhead vacuum tank E to the dust collector x, whence it is drawn by the vacuum into the chamber x" through the seal of water, leaving the dust behind, and the purified air is drawn by pipe H to the exhauster. Water is fed into the under part of the dust collector x by a small pump. By this arrangement dusty air is prevented from entering the exhauster. This is very important, as the dust from grain contains a large percentage of silica, which naturally causes wear and tear if it gets into the cylinder. Figs. 291, 292, and 293. Haviland & Farmer’s Air Trap. The arrangement of the dust collectors admits of either eliminating the dust altogether, or if need be, returning it to the cargo of grain, so as not to diminish the weight. The dust in the latter case is only held in suspension at the time, and then put back with the discharged grain. The importance of this improvement is apparent, as merchants have sometimes complained of the loss of weight where pneumatic machinery has been used for unloading cargoes. The air trap employed consists of a revolving wheel valve, Figs. 291, 292, and 293, which contains eight pockets in its circumference. These fit into a casing, and the wheel is driven at a suitable speed by power from the engine, so that the capacity of the revolving pockets is about equal to that of the grain discharged from the exhaust chamber. It is obvious that a valve of this description can be made to fit more nearly air-tight than the Duckham trap, and therefore loss by leakage is much reduced. This air-lock has the additional advantage that the pockets are much smaller than those in the Duckham air trap. Hence, though the filling of each individual bucket has to be effected more frequently, the amount of air carried into the exhaust chamber is less at each time. Thus the draught is not so severe even if used for the purpose of causing a winnowing effect, while the call upon the exhauster is more uniform. Of course with both the Duckham and Haviland & Farmer air traps, the pocket to be filled with grain before going into register with the exhaust chamber is full of air of atmospheric pressure, and it is obvious that the exhauster must remove this air in order to keep the vacuum