Changing the machinability and workability of a coal bed, by varying the thrust applied to the roof

摘要

In order to provide a free choice of the bed stresses in coal mining and particularly in coal longwalls, depending on the character of the bed, and thereby change the machinability and workability of the coal bed, the longwall working is divided along its length into blocks each of which has a support whose supporting properties depends upon the character of the bed in the block. In order to do this, hydraulic props are provided, each of which has an additional line (11) connected on one side to a main supply line (12) via a relief valve (10) whose relief ratio can be adjusted, and on the other side to a chamber (1) which is below the piston (2) of the prop; the pressure set by the relief valve (10) is less than a pressure set by a valve (5) connected to a line (14) for supplying hydraulic fluid to the chamber (1). IMAGE