In a rotary vane compressor, the rotor shaft is supported by white metal bearings, which ensure a quiet and longer operating life than roller bearings. Roller or taper bearings are needed in a screw compressor because the rotors have to operate at high speed with high axial accuracy and minimum clearance between the rotors, housing and endplates.
The machining of the rotors for screw compressors must be carried out with special and expensive tools. Machining of any vane compressor part can be performed with quality machine tools to ensure accuracy and inter-changeability of the parts. Any component can be replaced without changing the part to which it is adjacent. It is not the same for screw compressors, as the rotors are a "matched pair."
In screw compressors, wearing typically affects the rotors, roller bearings, the gear box and bearings and even the stator. Due to the inevitable wear of the bearings, the rotors may touch the cylinders in which they rotate, thereby resulting in replacement of the airend.