A device with blow stations disposed on a blow wheel for blow molding containers from a thermoplastic material includes a unit for pneumatic control of a blow pressure. The pneumatic control unit has a control piston which is guided in a cylinder and is mounted so as to be movable in the direction of a longitudinal axis of the piston. A main flow path, which can be closed by the control piston, extends through the cylinder. The control piston is provided with a control surface which faces a control chamber of the cylinder and is designed to transmit a control force to the control piston. The control piston is constructed at least in some regions from a metal or a ceramic.