An air-dryer cartridge for a compressed air preparation system of a utility vehicle includes a drying agent container having a first housing part and a second housing part movable relative to each other, a cartridge housing for holding the drying agent container, and a helical spring is arranged to preload the second housing part in a direction to reduce a volume of the drying agent container. The helical spring has multiple coils, including a first outer coil at a first end of the helical spring and a second outer coil at a second end of the helical spring. At least one of the first and second outer coils has a greater diameter than inner coils of the helical spring between the first and the second end of the helical spring.