Rock crushers

In a jaw crusher for crushing rock of the type having a frame, a fixed jaw mounted on the frame and a movable jaw mounted on the frame for movement toward and away from the fixed jaw between a first set position which determines the maximum size of the gap formed between the jaws for a predetermined jaw setting and a first advanced position in which the movable jaw is located more closely adjacent the fixed jaw, and wherein the movable jaw is movable from the first set position to a retracted position in which it is more remote from the fixed jaw than it is when it is in the first set position so as to facilitate the removal of obstructing material from the bite which is formed between the jaws, the improvement of;

• hydraulic control means for controlling the movement of the movable jaw between said first set position and said retracted position comprising;
• (a) a double acting hydraulic ram having first and second ends mounted on the frame and movable jaw respectively, and being extensible and contractable between said ends, said ram comprising a cylinder, a piston slidably mounted in the cylinder and dividing the cylinder into first and second fluid chambers, a rod extending from the piston and projecting from one end of the cylinder, one of said ends of said ram being located on said cylinder and the other being located on said rod, first and second fluid ports communicating with said first and second chambers respectively, movement of said piston resulting from expansion of said first fluid chamber serving to move the movable jaw to said first set position and movement of said piston resulting from expansion of said second fluid chamber serving to move the movable jaw to said retracted position,
• (b) a source of high pressure hydraulic fluid,
• (c) first fluid supply conduit means communicating between said source and said first fluid chamber to supply and vent hydraulic fluid from said first fluid chamber,
• (d) second fluid supply conduit means communicating between said source and said second fluid chamber to supply and vent hydraulic fluid from said second fluid chamber,
• (e) flow control means in said first and second fluid supply conduit means for simultaneously locking hydraulic fluid in said first and second fluid supply conduits to hold the extensible ram in a substantially rigid fixed length condition when in said set position during normal operation of the crusher,
• (f) non-pneumatic pressure relief means communicating with said first fluid chamber to relieve the pressure in said first fluid chamber when the pressure in said first fluid chamber exceeds a predetermined control pressure to free the movable jaw for movement toward said retracted position.