Hydraulic drive systems for mineral mining machines

Claim 1

A FLUID PRESSURE DRIVE SYSTEM INCLUDING A PUMPING MEANS, A POWER MEANS COUPLED TO THE PUMPING MEANS, A FLUID PRESSURE MOTOR, A FLUID-CONDUCTING CIRCUIT BY WHICH THE PUMPING MEANS AND THE FLUID PRESSURE MOTOR ARE CONNECTED TO ONE ANOTHER, A CONTROL VALVE HAVING AT LEAST ONE OPERATIVE POSITION AND AN "OFF" POSITION INTERCALATED IN THE FLUID-CONDUCTING CIRCUIT, AND A THRUSTING DEVICE INCORPORATING A MOVABLE MEMBER MOVABLE BETWEEN TWO EXTREME POSITIONS TO ONE OF WHICH IT IS BIASED, ONE OF SAID POSITIONS BEING AN OPERATIVE POSITION IN WHICH THE MOVABLE MEMBER IS ENGAGEABLE WITH THE CONTROL VALVE MECHANISM TO OPERATE SAID MECHANISM TO A CAUSE THE CONTROL VALVE TO MOVE TO THE "OFF" POSITION IF IT IS NOT ALREADY IN THAT POSITION AND THE OTHER BEING AN INOPERATIVE POSITION IN WHICH THE MOVABLE MEMBER IS OUT OF ENGAGEMENT WITH THE CONTROL VALVE MECHANISM, THE MOVABLE MEMBER BEING CONNECTED INTO THE FLUID-CONDUCTING CIRCUIT IN SUCH A WAY THAT ANY PRESSURE COMMUNICATED TO THE THRUSTING DEVICE FROM THE FLUID-CONDUCTING CIRCUIT TENDS TO MOVE THE MOVABLE MEMBER IN THE OPPOSITE DIRECTION TO THAT TO WHICH IT IS BIASED, AND THE THRUSTING DEVICE BEING SO ARRANGED THAT AS A RESULT OF THE PARTICULAR PRESSURE CONDITIONS EXISTING IN THE FLUID-CONDUCTING CIRCUIT DURING OPERATION OF THE PUMP THE MOVABLE MEMBER IS IN THE INOPERATIVE POSITION, AND WHEN SAID PRESSURE CONDITIONS CHANGE AS A RESULT OF STOPPAGE OF THE PUMP THE MOVABLE MEMBER IS MOVED TO THE OPERATIVE POSITION.