For regulating the pressure in a pressure chamber, in particular in a pneumatic brake apparatus for a web-type recording medium, an actual pressure is set in the pressure chamber dependent on an actual angle of rotation of a rotary valve. The actual angle of rotation of the rotary valve and the actual pressure in the pressure chamber are acquired. A target pressure and a target angle of rotation allocated to this target pressure are predetermined, and a pressure deviation between the actual pressure and the target pressure are determined, as is a deviation of the angle of rotation between the actual angle of rotation and the target angle of rotation. An adjusting unit sets the angle of rotation at the rotary valve, first dependent on the deviation of the angle of rotation and then dependent on the pressure deviation. Furthermore, a sensor for acquiring the angle of rotation is specified.