Hydraulic mine roof supports

Claim 1

A MINE ROOF SUPPORT INCLUDING A ROOF-ENGAGING STRUCTURE HAVING A PIVOTALLY MOUNTED EXTENSION PIECE, A PRESSURE-FLUID RAM FOR APPLYING SAID EXTENSION PIECE TO THE ROOF AND A PRESSURE INTENSIFIER, FOR SAID PRESSUREFLUID RAM, COMPRISING, AS A COMPACT AND ROBUST INTEGRAL UNIT, TWO CYLINDERS ONE OF WHICH HAS A LARGER BORE DIAMETER THAN THE OTHER, PISTONS WORKING IN SAID CYLINDERS, A PRESSURE-FLUID DISCHARGE ORIFICE IN THE SMALLER CYLINDER CONNECTED TO SAID PRESSURE-FLUID RAM FOR THE SUPPLY OF PRESSURE-FLUID THERETO, A PRESSURE-FLUID INLET OPENING IN THE LARGER CYLINDER FOR PRESSURE-FLUID TO ACT ON THE PISTON THEREIN AND MOVE IT AND THE PISTON IN THE SMALLER CYLINDER TOWARDS THE EXHAUST ORIFICE, MEANS ACTING TO MOVE SAID PISTONS IN THE OPPOSITE DIRECTION, A COMMUNICATING PASSAGE BETWEEN THE TWO CYLINDERS, AND A ONE-WAY VALVE IN SAID PASSAGE PERMITTING FLOW OF FLUID FROM THE LARGER CYLINDER TO THE SMALLER CYLINDER, BUT NOT IN THE REVERSE DIRECTION, UNTIL THE PRESSURE AT SAID INLET OPENING EQUALS THE PRESSURE AT SAID DISCHARGE ORIFICE WHEREUPON THE VALVE CLOSED AND THE PRESSURE ACTING ON HE LARGER PISTON CAUSES IT TO MOVE THE SMALLER PISTON SO AS TO INCREASE THE PRESSURE AT THE PRESSURE-FLUID DISCHARGE ORIFICE IN RELATION TO THE PRESSURE AT THE INLET OPENING WHEREBY AN INTENSIFIED FLUID-PRESSURE IS SUPPLIED TO SAID PRESSURE-FLUID RAM AND THEREBY TO THE ROOF THROUGH SAID PIVOTALLY MOUNTED EXTENSION PIECE OF THE ROOF-ENGAGING STRUCTURE.