Mine-roof support control means

Mine-roof support control means comrising:

• (a) a main control unit incorporating a pressure-controlled valve;
• (b) a workstage control device connected thereto and comprising a 3/2 switching-on valve, a 3/2 switching-off valve and a 3/2 transmitting valve, said 3/2 valves of the control device being alternately connectable to a high-pressure fluid line and to a low-pressure fluid return line in order to convert a pressure pulse into a switching step at the main control unit and for transmitting an answering pressure pulse signalling the completion of a workstage for continuing a sequence of operations;
• (c) respective means for actuating the switching-on valve and the switching-off valve, said actuating means each including a fluid cylinder containing twin operating pistons;
• (d) means for actuating the transmitting valve comprising a fluid cylinder containing one operating piston;
• (e) fluid connections on said valves to provide for the return line to communicate with the switching-on valve and the transmitting valve in their inoperative positions and with the switching-off valve in its operating postion;
• and
• (f) fluid connections between the switching-on valve, the switching-off valve and the transmitting valve to ensure that, when a first one of the two actuating pistons of the switching-on valve is acted on by a pressure pulse, the switching-on valve communicates with the high pressure line and leads pressurised fluid to said pressure-controlled valve in the main control unit which actuates the workstage through the opened switching-off valve to the second actuating piston of the switching-on valve and to the actuating piston of the transmitting valve which opens to transmit the answering pressure pulse.