A pressurised air generating system comprises a chassis, an air compressor mounted on the chassis, a drive shaft drivably connected to the air compressor 38 where the drive shaft 4 has a drive input 5 for connection to a power take off unit of a tractor or agricultural vehicle and a mounting assembly for mounting the chassis to the tractor or agricultural vehicle. There may be a drive input on each end of the drive shaft. The mounting assembly may be engagable with the chassis such that it can be mounted to connect to either the front or rear power take off unit of the tractor. The drive shaft may project beyond the chassis. The mounting assembly may connect to a three point linkage on the tractor. The air compressor may be used to power pneumatic systems.
