Apparatus and method for expanding preforms into containers

Method for expanding preforms into containers (20) within a blow mould (1) by means of a pressurised pneumatic medium (MG),

• wherein
• during an expansion process for expanding the container (20), a compressor piston unit (11) for compressing the pneumatic medium (MG) is controlled by means of an actuator unit (12) that is driven by a hydraulic medium (MF) and interacts with at least one element of the compressor piston unit (11), in order to transport the pneumatic medium (MG) into an inner region of the blow mould (1), and that
• during a relaxation process that follows the expansion process, the pneumatic medium (MG) is returned into the compressor piston unit (11), as a result of which the actuator unit (12) is caused to a return of the hydraulic medium (MG)
• and wherein the actuator unit (12) itself comprises an actuator piston element (12b) and an actuator medium space (12a) within a hydraulic medium (MF) is introduced in order to move the actuator piston element (12b) in such a way that the movement of the actuator piston element (12b) also moves the piston element (11b) of the compressor piston unit (11) which is in operative connection with the actuator piston element (12b) so that during an expansion process of the container to be expanded the piston element (11b) of the compressor piston unit (11) compresses a pneumatic medium (MG) present in the compression space (11a) which is then transferred to a blow nozzle or to a blow mold (1).