Hydraulically operated- unit

Claim 1

A HYDRAULICALLY OPERATED UNIT FOR USE WITH ELEVATING PLATFORM LIFTS, SAID UNIT COMPRISING A VERTICAL SINGLE ACTING CYLINDER, A HOLLOW PLUNGER PISTON LONGITUDINALLY MOVABLE WITHIN SAID CYLINDER, A LOWER HEAD MOUNTED ON SAID PISTON, SAID HOLLOW PISTON COMPRISING A FLUID RESERVOIR FOR OPERATING FLUID, A FLUID PUMP ARRANGED BETWEEN SAID CYLINDER AND THE RESERVOIR IN SAID PISTON, A MOTOR FOR DRIVING SAID PUMP, SAID MOTOR BEING REVERSIBLE SO AS TO DRIVE SAID PUMP IN EACH OF TWO OPPOSITE DIRECTIONS, SAID PUMP HAVING A FIRST PORT AND A SECOND PORT, ONE OF SAID FIRST AND SECOND PORTS SERVING AS AN INLET AND THE OTHER AS AN OUTLET IN A FIRST DIRECTION OF OPERATION OF SAID PUMP AND THE ONE PORT SERVING AS AN OUTLET AND THE OTHER AS AN INLET IN THE SECOND DIRECTION OF OPERATION OF SAID PUMP, AN INLET PASSAGE CONNECTING EACH OF SAID PORTS WITH THE INTERIOR OF SAID PISTON, A CHECK VALVE IN EACH OF SAID INLET PASSAGES TO PERMIT THE FLOW OF FLUID TOWARD THE PUMP ONLY, EACH OF SAID CHECK VALVES HAVING A RESTRICTED BLEED PASSAGE THEREAROUND, AN OUTLET PASSAGE CONNECTED TO EACH OF SAID PORTS, A CONTROLLABLE CHECK VALVE IN EACH OF SAID OUTLET PASSAGES, ONE OF SAID OUTLET PASSAGES COMMUNICATING WITH THE INTERIOR OF SAID CYLINDER, THE OTHER OF SAID OUTLET PASSAGES COMMUNICATING WITH THE INTERIOR OF SAID PISTON, SAID CONTROLLABLE CHECK VALVE IN SAID OTHER OUTLET PASSAGE BEING CONTROLLED TO CLOSE DURING A LIFT OPERATION BY THE PRESSURE OF SAID PISTON OPERATING IN A FIRST CONTROL PASSAGE LEADING THERETO FROM SAID ONE OUTLET PASSAGE DOWNSTREAM OF SAID CONTROLLABLE CHECK VALVE IN SAID OUTLET PASSAGE, THE CONTROLLABLE CHECK VALVE IN SAID ONE OUTLET PASSAGE BEING MAINTAINED OPEN DURING THE DESCENT OF SAID LIFT UNIT BY PRESSURE IN A SECOND CONTROL PASSAGE LEADING THERETO FROM SAID OTHER OUTLET PASSAGE CONTAINING A CONTROLLABLE CHECK VALVE AND UPSTREAM THEREOF, AND SAFETY PRESSURE RELEASE MEANS CONNECTED TO EACH OF SAID PORTS TO RELEASE EXCESSIVE FLUID PRESSURE.