The disclosure relates to a device and a method for controlling the throughflow of blow-molding fluid during the blow molding of containers. It is the intention to provide a control device and a control method which permit a controlled or defined growth and a defined propagation of the container bubble formed by the expanding preform in the pre-blowing phase of the blow molding process without the specification of a specific setpoint value profile or of a setpoint value curve. The object is achieved by means of a control device and a control method having a proportional valve with a variable throughflow cross section, having an actuator for the operation of the proportional valve, having a means for detecting the position of the actuator, and having sensor means for detecting the valve inlet and valve outlet pressure, wherein a time for the attainment of the yield point for the preform, a container volume and a time period for the attainment of the container volume are predefinable, and, by means of a digital controller, during the pre-blowing phase, from the attainment of the yield point until the run duration, a calculation of control values for the operation of the actuator in order to attain the predefined container volume within the predefined time period is performed in automated cyclic fashion, and the actuator is operated in accordance with the calculated control values, wherein, in each calculation cycle, the calculation of the respectively next control value is performed taking into consideration the container volume attained prior to the respective calculation cycle and calculated on the basis of the previous actuator positions and the previous pressure profile.
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