Fluid pressure actuated operator cylinder with incorporated stress converter

An operator cylinder comprising a casing, said casing comprising three adjacent and successive coaxial sections, two end heads at opposite ends of said casing, two intermediate walls separating said sections, a first pneumatic piston movable in a cylinder comprised by said first section, said first piston having a piston rod comprising an operator stem thereon that extends through and beyond the adjacent said end head, said first piston having a hydraulic plunger thereon that extends into said second section, an annular idle hydro-pneumatic piston that slides within a cylinder comprised by said second section, said annular piston sealingly surrounding a hydraulic cylinder within said second section, said hydraulic plunger sealingly sliding within said hydraulic cylinder, a second pneumatic piston disposed in a cylinder comprised by said third section, feed passages formed in said heads and in said intermediate walls to supply air under pressure to opposite sides of said first and second pneumatic pistons and to the same side of said annular piston as said first piston and to supply hydraulic fluid under pressure to said second section on the opposite side of said annular piston and to the interior of said hydraulic cylinder, means establishing hydraulic communication between the interior of said hydraulic cylinder and said other side of said annular piston, means actuated by said second pneumatic piston for transmitting to said hydraulic fluid in said hydraulic cylinder a pressure higher than the air pressure to which said first piston is subjected, and cutting off means cooperating with said transmitting means in order to cut-off said communication between said hydraulic cylinder and said annular piston during operation of said transmitting means.