An image data compression technique is disclosed in which image data compression is based at least partially upon information encoded in a descriptive portion of an image data file. The brackets run along tracks secured to the building and engage the tracks to assume a variety of elevations. An estimated manifold pressure is calculated from the MAF, the IAT, and the initialized MAC. When the injection valve element is closed, the control piston opens a main connection with a large flow cross section and when the injection valve element is open, this control piston closes the main connection, only opening a bypass connection with small flow cross section, the bypass connection is embodied in a housing part delimiting the control pressure chamber.