Hydraulic control systems for use with mining apparatus

For use with mineral mining equipment having a series of double-acting hydraulic rams for shifting a conveyor, each ram having a first working chamber which is charged with pressure fluid to extend the ram and a second chamber which is charged with pressure fluid to retract the ram, an improved hydraulic control system for operating the rams, said system comprising:

• a. at least one pressurized source of hydraulic fluid;
• b. main pressure fluid feed conduit means connected to said at least one pressurized source;
• c. pressure fluid return conduit means connected to said at least one pressurized source;
• d. further pressure fluid feed conduit means connected to said at least one pressurized source;
• e. regulating means for varying the pressure of the fluid in said further conduit means;
• and
• f. a plurality of control devices each associated with at least one of the rams and connected to the working chambers of the rams on the one hand, and connected to said main conduit means, and to said further conduit means, and to said return conduit means on the other hand, each said control device selectively connecting the working chambers with various combinations of said conduit means, each said control device having three intake ports and two outlet ports, said first intake port connected to said main conduit means, said second intake port connected to said further conduit means, and said third intake port connected to said return conduit means;
• said first outlet port connected to the second working chamber of the associated ram, and said second outlet port connected to the first working chamber of the associated ram, each said control device adjusting to three operative states comprising:
• a first state wherein said first intake port is connected to said first outlet port, said second intake port is connected to said second outlet port, and said third intake port is blocked;
• a second state wherein said third intake port is connected to both said first and said second outlet ports, and said first and said second intake ports are blocked;
• and a third state wherein said first intake port is connected to said first outlet port, said third intake port is connected to said second outlet port, and said second intake port is blocked;
• and wherein adjusting said control device to the first state causes the ram to extend, and adjusting said control device to the third state causes the ram to retract.