Flexible dynamic seal

Claim 1

IN AN EXTENSIBLE AND RETRACTABLE FLUID PRESSURE OPERATED ACTUATOR, A CYLINDER, A PISTON MEMBER AXIALLY MOVABLE IN SAID CYLINDER, AN ANNULAR RESILIENT RADIALLY EXPANDABLE PISTON RING IN THE PERIPHERY OF SAID PISTON IN SURROUNDING UNEXPANDED CONDITION IN SUBSTANTIALLY FREE SLIDING RELATION TO THE INNER WALL OF THE CYLINDER RETARD PRESSURE LEAKAGE AROUND SAID PISTON BETWEEN THE OPPOSITE ENDS OF THE CYLINDER DURING RELATIVE MOVEMENT OF SAID PISTON BY THE INTRODUCTION OF PRESSURE FLUID INTO EITHER END OF SAID CYLINDER, PRESSURE FLUID SUPPLY MEANS FOR NORMALLY EXPANDING SAID PISTON RING OUTWARDLY INTO PREDETERMINED FRICTIONAL AND FLUID SEALING CONTACT WITH THE INNER WALL OF THE CYLINDER WHEN SAID PISTON IS AT REST IN SAID CYLINDER TO FRICTIONALLY RESIST MOVEMENT OF SAID PISTON IN SAID CYLINDER AND RESIST PRESSURE FLUID LEAKAGE AROUND SAID PISTON BETWEEN THE OPPOSITE ENDS OF SAID CYLINDER WHEN SAID PISTON IS AT REST, COMMON SLIDABLE VALVE MEANS IN SAID PISTON FOR SELECTIVELY ADMITTING PRESSURE FLUID INTO EITHER END OF SAID CYLINDER FOR MOVING SAID PISTON AND SIMULTANEOUSLY VENTING SAID PISTON RING EXPANDING PRESSURE FLUID SUPPLY MEANS TO ALLOW CONTRACTION OF SAID RESILIENT PISTON RING TO ITS NORMAL UNEXPANDED CONDITION TO ELIMINATE FRICTIONAL CONTACT BETWEEN SAID PISTON RING AND SAID CYLINDER DURING SELECTIVE AXIAL MOVEMENT OF SAID PISTON IN EITHER DIRECTION