The Mechanical Handling and Storing of Material

254 THE MECHANICAL HANDLING OF MATERIAL as soon as the roller comes in contact with any obstruction on the line. By the com- pression of the spring, caused by such obstruction, the two levers which hold the sides of the truck are released, and thus allow the latter to open outwards. 1 he unloading contrivance consists of a short inclined plane d made of flat iron (Fig. 367), which is fitted in the middle between the lines of rails, at the point where the trucks are to be unloaded, and in this way the discharge of the coal is effected at any one of the three destinations. The closing of the side doors of the trucks is also effected automatically. For this purpose immediately beyond each delivery point there are fitted on both sides of the track oblique rails e (Fig. 369), at the height of the lower edge of the movable sides a, a of the truck, and at the end of these rails are fitted two rollers with powerful springs. As the truck passes with open doors, the rails e gently close the doors by pressing them behind the levers b. In consequence of the sharp curves to be negotiated, the tubs are kept rather short, and the distance between the axles is such that it is not possible for the back wheels to be lifted off the rails by any pressure of the rope on the clip which is fitted to the front. The tubs are entirely of iron, and weigh over 13 cwt., having a capacity of about 17f cwt. The ropes are driven at the rate of 100 ft. per minute by a double-grooved pulley connected by a suitable gearing to a small steam engine. From this driving pulley the rope passes over two guide pulleys in a downward and upward direction. At the bottom of the loop thus formed is another guide pulley, which is weighted for the purpose of tightening the rope, which then passes to the commencement of the track, where there are two more guide pulleys, one of which guides the full rope, while the other guides the return rope. With the exception of the wheels supporting the return strand, all the pulleys are grooved and lined with leather, which is stamped out in small pieces, which stand on end and form grooves in the bottom of these rope pulleys. This arrangement has been found to effectually prevent any slipping of the rope.