The invention relates to a compressed air preparation device for rail vehicles or utility vehicles, comprising a compressed air inlet, to which an air compressor can be connected, a compressed air outlet, which is connected to the compressed air inlet via a compressed air duct, and an air drying device arranged in the compressed air duct. In the event that the air compressor is switched off, the compressed air duct is vented upstream of the air drying device so that, at restart, the air compressor can start against a reduced counterpressure.