Drilling machine

Claim 1

IN A ROCK-DRILLING MACHINE HAVING A FRAME, A DRILL CARRIED BY THE FRAME FOR TRAVEL THEREALONG, A FLUID-ACTUATED REVERSIBLE FEED MOTOR HAVING "FORWARD" AND "REVERSE" LINES AND ADAPTED TO MOVE THE DRILL ALONG THE FRAME, AND A CONSTANT-FLOW PUMP HAVING SUPPLY AND RETURN LINES; THE IMPROVEMENT THAT COMPRISES A THREE-POSITION MAIN CONTROL VALVE CONNECTED TO THE SUPPLY AND RETURN LINES OF THE PUMP, SAID FEED MOTOR HAVING ITS "FORWARD" AND "REVERSE" LINES CONNECTED TO THE MAIN CONTROL VALVE, THE MAIN CONTROL VALVE BEING MOVABLE FROM A STOP POSITION WHEREIN THE PUMP SUPPLY LINE IS DISCONNECTED FROM BOTH THE "FORWARD" AND "REVERSE" LINES OF THE MOTOR TO A FORWARD POSITION WHEREIN THE SUPPLY LINE OF THE PUMP IS CONNECTED TO THE "FORWARD" LINE OF THE MOTOR AND THE "REVERSE" LINE OF THE MOTOR IS CONNECTED TO THE RETURN LINE OF THE PUMP THEREBY TO ADVANCE THE DRILL, THE MAIN CONTROL VALVE ALSO BEING MOVABLE FROM THE STOP POSITION TO A REVERSE POSITION WHEREIN THE MOTOR CONNECTIONS ARE REVERSED, THEREBY TO RETRACT THE DRILL, AND AN ADJUSTABLE BY-PASS VALVE CONNECTED ONLY BETWEEN THE FORWARD LINE OF THE MOTOR AND THE RETURN LINE OF THE PUMP, THEREBY TO BLEED OFF A PREDETERMINED SELECTED QUANTITY OF THE CONSTANT PUMP FLOW, WHEREBY CONTROL OF THE RATE OF DRILL ADVANCE IS REDUCED TO A PRE-SET VALVE WHEN THE MAIN CONTROL VALVE IS IN THE FORWARD POSITION WITHOUT LIMITING THE RATE OF DRILL RETRACTION WHEN THE MAIN CONTROL VALVE IS IN THE REVERSE POSITION.