Control system for hydraulic actuators

Claim 1

HYDRAULIC APPARATUS COMPRISING IN COMBINATION A HYDRAULIC ACTUATOR HAVING AN ACTIVE STROKE AND A RETURN STROKE AND COMPRISING A WORKING CHAMBER OF VARIABLE VOLUME, A HIGH-PRESSURE SOURCE OF HYDRAULIC LIQUID, A LOWPRESSURE RECEIVER OF LIQUID EXHAUSTED FROM THE ACTUATOR, A TWO-POSITION SELECTOR COCK FOR SELECTIVELY CONNECTING THE WORKING CHAMBER OF THE ACTUATOR ALTERNATELY TO THE HIGHPRESSURE SOURCE AND TO THE RECEIVER, DUCTING CONNECTING SAID SELECTOR COCK WITH SAID WORKING CHAMBER, SAID DUCTING COMPRISING FOR THE SMALLER PART OF ITS LENGTH A COMBINED FEED AND EXHAUST PIPE CONNECTED TO SAID WORKING CHAMBER AND OF SUCH VOLUMETRIC CAPACITY THAT THE QUANTITY OF HYDRAULIC LIQUID FILLING SAID PIPE IS SMALLER THAN THE QUANTITY OF HYDRAULIC LIQUID EXPELLED FROM THE WORKING CHAMBER DURING THE RETURN STROKE OF THE ACTUATOR, AND FOR THE GREATER PART OF ITS LENGTH TWO PARALLEL BRANCHES, NAMELY A FIRST AND A SECOND BRANCH, SAID SECOND BRANCH BEING CONNECTED DIRECTLY TO SAID RECEIVER AND SAID FIRST BRANCH BEING SELECTIVELY CONNECTIBLE THROUGH SAID SELECTOR COCK TO SAID SOURCE AND TO SAID RECEIVER ALTERNATIVELY, A CYLINDER COMMUNICATING WITH SAID FIRST BRANCH, A PISTON IN SAID CYLINDER, A VALVE OPERATIVE BETWEEN SAID SECOND BRANCH AND SAID WORKING CHAMBER, SAID VALVE BEING SO ACTUATED BY SAID PISTON AS TO BE URGED TO CLOSED POSITION BY THE PRESSURE IN SAID CYLINDER AND TO OPEN POSITION BY THE PRESSURE IN SAID SECOND BRANCH, A BY-PASS CONNECTING SAID WORKING CHAMBER WITH SAID CYLINDER AND FIRST BRANCH AND A NON-RETURN VALVE IN SAID BY-PASS PREVENTING FLOW FROM SAID WORKING CHAMBER TOWARDS SAID CYLINDER AND FIRST BRANCH.