Control for a hydraulic prop of advancing mine roof supports

摘要

The prop (1) is controlled by a resetting device (10) which is inserted in parallel connection with the setting and withdrawal valves (4, 8) into the resetting line (11) leading to the pressure space (2) of the prop (1). The resetting operation is activated by the actuation of a control plunger (14) at the resetting device (10) which connects a 3/2-way directional control valve (13) to the high-pressure line P. The inflowing pressure fluid acts upon the control piston (16) from a further 3/2-way directional control valve (15) which directs pressure fluid to the pressure space (2) of the prop (1) and to a control piston (17). The latter acts on a bar (18) which engages in a recess (19) of the control plunger (14) against the force of a retaining spring (20) if the pressure in the resetting line (11) exceeds a predetermined minimum setting pressure. The bar (18) is disengaged by loading a control piston (23) with the withdrawal valve (8).