The Mechanical Handling and Storing of Material

212 THE MECHANICAL HANDLING OF MATERIAL movement, so that when H1 receives its load its exit k.1 is closed, and the inlet to h is closed whilst it discharges its load through k, which is open. Fig. 283 shows not only the delivery of grain by suction, but also its further dis- charge into granaries, etc., by air pressure. Thus the apparatus is illustrated in the form in which it has been used for the combined system of blast and suction. The tank M, which receives the grain alternately through the pipes K and K1, is connected with pipe E, which forces the compressed air into the tank, and by the use of pipe J leads the grain and air away to its destination. The grain can also be withdrawn by n. This would only be the case were the apparatus in use under suction alone. The ports G, G1 and e, e1 are for thus equalising the pressure between b purpose of establishing communication, and h, h1 during the filling, or rather just before the filling operation takes place, and between m and h, h1 just be fore the discharge begins. In the later types the air traps- in use with the Duckham pneu- matic elevators, especially those for suction only, have been much sim- plified; their present construction is shown in Fig. 284. The illus- tration shows the rocking air trap in the two positions, one in full and the other in dotted lines. The exits from the two compartments d and d1 are hinged flap doors with india-rubber linings. They are held closed through the vacuum within during loading. When one compartment is full the whole ap- paratus falls over to the other posi- tion, and in so doing first shuts off the inflow of grain and with it the vacuum, and then opens a port x which establishes communication, with the outer atmosphere, upon which the valve d1 opens and allows- the and Fig. 284. Duckham’s Pneumatic Air Trap. the load to discharge. The partition between the two compartments is weighted, thus restraining the action of the apparatus until the compartment is full, when the weight of the grain overbalances it. This appliance has done excellent work, but as the air in the oscillating pockets has not been withdrawn, as in the apparatus previously men- tioned, it happens that as soon as the empty pocket is brought into communication with the vacuum chamber, the air contained in the pocket expands rapidly into the vacuum chamber and thus causes a violent disturbance to the grain in the latter.. The apparatus being automatic or self-acting requires a comparatively loose fit, and it is difficult there- fore to make it anything like air-tight, and such leakage means a great waste of driving power. However, the extreme simplicity of this trap was something in its favour. Fig. 285 shows the construction of the suction nozzle which explains itself, the action being similar to that of an injector. The suction pipe which connects this nozzle with the vacuum chamber is about 6 in. in diameter, and consists of plain wrought-