to impeller shaft 13 impeller shaft 13 runs in high speed bearings 37 and 38 bearings 37 and 38 are mounted inside the input sprocket 60 impeller shaft 13 and input sprocket 60 rotate in the same direction therefore the demand to the high speed bearings 37 and 38 can be reduced and cheaper bearings of standard quality can be used input sprocket 60 runs in bearings 24 and 25 and has a groove 47 towards the small high speed sprocket 36 where the air can escape to avoid axial belt guidance on the small high speed sprocket 36 the input sprocket 60 has a chamfer 45 and the larger sprocket 33 has on the opposite side a flange 49 fig6 and 7 show a third embodiment and will now be described if very high durability is needed the load on the high speed bearings has to be reduced one way of doing this is by fitting a second idler shaft in an opposite position to the other then the forces from the belt pull on the output sprocket can be almost eliminated further the load on the inner input shaft bearing can be almost removed then a less space demanding bearing can be used this embodiment is able to provide very high durability in a lightweight and quiet solution that runs oil free production cost compared to other type of high pressure compressors is very low the.