The compressor has a number of pistons (12) driven by a drive shaft (21) in a casing. The casing is composed of a number of components (1,3,6) arranged along the axis of the drive shaft, in contact with each other to form the casing. There is a device to suppress the bending moment induced in some of the components when the components are pressed together parallel to the drive shaft axis. The contact surfaces on the casing components are arranged opposite each other so that the contact surfaces are at an angle to the axis of the drive shaft. There is also a fixing device (9) to press the components together.
