Piston cylinder assembly

Claim 1

A HYDRAULIC POWER-TRANSMITTING DEVICE COMPRISING TWO MEMBERS, A PISTON AND A CYLINDER, ONE OF THE MEMBERS BEING SLIDABLE RELATIVE TO THE OTHER MEMBER, BACKER MEANS POSITIONED ADJACENT THE FACE OF THE PISTON, A FLUID CHAMBER WITHIN THE CYLINDER, ONE WALL OF WHICH IS DEFINED BY THE PISTON, A PORT THROUGH THE CYLINDER WALL FOR ADMITTING HYDRAULIC FLUID INTO THE CHAMBER, A SOFT MATERIAL CUP MEMBER OF LESS THAN FIFTY DUROMETER HARDNESS, THE CUP MEMBER HAVING A BASE POSITIONED ADJACENT THE BACKER MEANS AND HAVING AN ANNULAR SIDE WALL THAT BEARS AGAINST THE SIDE WALL OF THE CYLINDER, AN EXPANDER FOR BIASING THE SIDE WALL OF THE CUP MEMBER AGAINST THE SIDE WALL OF THE CYLINDER, THE CUP MEMBER BEING OF A SUFFICIENTLY SOFT MATERIAL THAT, WHEN SUBJECTED TO SUBSTANTIAL FLUID PRESSURE WITHIN THE CHAMBER A SUBSTANTIAL LOCK IS APPLIED BY THE ANNULAR SIDE WALL OF THE CUP AGAINST THE SIDE WALL OF THE CYLINDER TO SUBSTANTIALLY PREVENT MOVEMENT OF THE SIDE WALL OF THE CUP RELATIVE TO THE SIDE WALL OF THE CYLINDER, AND TO CAUSE THE BASE OF THE CUP MEMBER TO EXPAND AND MOVE THE PISTON IN RESPONSE TO THE SAID SUBSTANTIAL FLUID PRESSURE, THE BACKER MEANS HAVING A SIDE WALL IN CONTACT WITH THE SIDE WALL OF THE FLUID CHAMBER FOR PREVENTING EXTRUSION OR FLOW OF THE CUP INTO THE SPACE BETWEEN THE CYLINDER WALL AND THE PISTON WALL.