Actuating unit of the articulated lever or cam type comprising - an actuator arm rotatable between an open position and a closed operating position; - a housing body inside of which a closing device configured to bring the actuator arm into rotation between the open position and the closed operating position is housed, wherein the closing device comprises a mechanism of movement irreversibility configured to trigger when the actuator arm reaches the closed operating position; and - a fluid-dynamic actuator configured to control the movement of the closing device, the fluid-dynamic actuator comprising a cylindrical body which extends between a first free head located at a free end of the cylindrical body and a second head for connection with the housing body ; and a piston housed in a translatable manner inside the cylindrical body , wherein the piston carries a first retaining element configured to engage a second retaining element housed inside the free head , the second retaining element being movable between an engagement position and a position of disengagement from the first retaining element , characterized in that it comprises a pusher element configured to bring the second retaining element into the position of disengagement from the first retaining element , wherein the pusher element is configured and/or housed in the fluid-dynamic actuator such that it is operable by means of a pressurized fluid, and is housed in the free head so as to intercept a fluid flow between a pressurized fluid supply mouth and an inner chamber of the cylindrical body in which the piston is housed, wherein the pusher element is movable between a rest position in which it obstructs the passage of pressurized fluid to the inner chamber of the cylindrical body and a thrust position in which it frees the passage of pressurized fluid to the inner chamber of the cylindrical body . - an actuator arm rotatable between an open position and a closed operating position; - a housing body inside of which a closing device configured to bring the actuator arm into rotation between the open position and the closed operating position is housed, wherein the closing device comprises a mechanism of movement irreversibility configured to trigger when the actuator arm reaches the closed operating position; and - a fluid-dynamic actuator configured to control the movement of the closing device, the fluid-dynamic actuator comprising a cylindrical body which extends between a first free head located at a free end of the cylindrical body and a second head for connection with the housing body ; and a piston housed in a translatable manner inside the cylindrical body , wherein the piston carries a first retaining element configured to engage a second retaining element housed inside the free head , the second retaining element being movable between an engagement position and a position of disengagement from the first retaining element , characterized in that it comprises a pusher element configured to bring the second retaining element into the position of disengagement from the first retaining element , wherein the pusher element is configured and/or housed in the fluid-dynamic actuator such that it is operable by means of a pressurized fluid, and is housed in the free head so as to intercept a fluid flow between a pressurized fluid supply mouth and an inner chamber of the cylindrical body in which the piston is housed, wherein the pusher element is movable between a rest position in which it obstructs the passage of pressurized fluid to the inner chamber of the cylindrical body and a thrust position in which it frees the passage of pressurized fluid to the inner chamber of the cylindrical body . <EOS>