Control system for load lifting apparatus

Claim 1

IN A COMBINATION OF THE CLASS DESCRIBED, A FLUID PRESSURE SOURCE HAVING A HIGH PRESSURE SIDE AND A LOW PRESSURE SIDE, A PRIMARY UPRIGHT EXTENDING FROM A BASE, A SECONDARY UPRIGHT MOVABLY MOUNTED ON SAID PRIMARY UPRIGHT, A LOAD CARRIAGE MOVABLY MOUNTED ON SAID SECONDARY UPRIGHT, A MAIN HYDRAULIC RAM OPERABLE BETWEEN SAID PRIMARY UPRIGHT AND SAID SECONDARY UPRIGHT FOR MOVING SAID SECONDARY UPRIGHT RELATIVELY TO SAID PRIMARY UPRIGHT, A SECOND HYDRAULIC RAM OPERABLE BETWEEN SAID SECONDARY UPRIGHT AND SAID LOAD CARRIAGE FOR MOVING SAID LOAD CARRIAGE RELATIVELY TO SAID SECONDARY UPRIGHT, OPERATING VALVE MEANS FOR SAID RAMS, THE MOVEMENT OF SAID OPERATING VALVE MEANS TO PARTICULAR LIFT POSITIONS DIRECTING FLUID FROM THE HIGH PRESSURE SIDE OF SAID PRESSURE SOURCE TO ONE OF SAID RAMS WHILE THE OTHER RAM REMAINS INOPERATIVE, CONTROL VALVE MEANS FOR SAID RAM, AND MEANS WHEREBY THE OPERATION OF EITHER OF SAID RAMS TO A PARTICULAR EXTENDED POSITION ACTUATES SAID CONTROL VALVE MEANS TO EFFECT THE MOVEMENT OF FLUID TO THE OTHER RAM DURING POSITIONING OF SAID OPERATING VALVE IN LIFT POSITION SO THAT THE TWO RAMS OPERATE AUTOMATICALLY IN SEQUENCE REGARDLESS OF WHICH RAM IS FIRST ENERGIZED.