The Mechanical Handling and Storing of Material

THE MECHANICAL HANDLING OF MATERIAL lower end. Two small openings may be seen in the main cylinder near the back and front ends ; these com- municate by means of channels with the valve box. As soon as the main piston has uncovered the first of these openings, some of the air passes under the piston of the slide gear and raises the same (see lower section) and thereby cuts off the air supply, and the main piston completes its stroke by the expansion of the air in the cylinder, and at the end of the stroke uncovers an exit (not shown in the illustration) for the air. In the second position (see lower section) air is admitted over the small lower pin-like plunger, which is pressed down, holding the remainder of the cylindrical slide block up. In this position air is at the same time admitted to the front end of the main piston, which thereby makes its return stroke. During this, as soon as the piston has closed the first of the ports, the enclosed air in front of the piston is compressed and forces the valve piston back into its first position again, when new air is admitted for the next stroke, and the same cycle repeated over and over again. With this engine the stroke can be varied by turning a semicircular disc which retards or accelerates the exit of the air. Working- Expenses.—As regards working ex- penses of reciprocating coal face conveyors (Rutschen), capacity, etc., the most reliable information available has been compiled by Arthur Gerke, a well-known engineer of Bochum, Germany, from his own tests, and from observations of cases which have come under his own notice in German mines. He says, when referring to the consumption of compressed air per minute, that the statements of the manufacturers of the different plants are very confusing. The quantity of air used, he says, does not so much depend upon the length of the conveyor, as on the condition of the coal. If large coal is handled the air consumption is much less than when dealing with fine coal, likewise the consumption is less with dry than with wet coal, and Mr Gerke attri- butes this circumstance to the greater friction caused by fine coal and wet coal. In addition to these considera- tions the consumption of air is variable with the number of strokes per minute. The following table1 is a résumé of air consumed, but as the quantity of coal handled was not taken into consideration, the result does not in any way prove the superiority of one conveyor over another, but only serves as a guide to the approximate air consumption. 1 From “ Ueber Abbauförderung,” by Arthur Gerke.