Rotary screw & vane compressors are not to be confused. The rotating screw compressor uses two meshed rotating positive-displacement helical screws to force a gas into a smaller space, whereas the other consist of a rotor with a number of blades inserted into radial slots in the rotor. A rotating screw compressor is at its best when it is new. At the stage of its life when it is relatively new, leakage is at a minimum. This is because with the new machine clearances are minimised. As the compressor gets more and more use, clearances get bigger due to friction wear and gas escapes through the intake end of the compressor. A rotating vane compressor, on the other hand, actually gets better as it gets worn. As the compressor blades seat themselves into the compressor’s slots, leakage is reduced causing the “worn in” compressor to be between five and ten per cent more efficient than when it was new. Since clearances are automatically maintained at a constant, there is no increase in air leakage with this type of compressor.

During start-up there is metal-to-metal contact in the screw type compressor. This is because the steel used for this type of compressor is not porous and so does not retain any lubrication oil, resulting in wear of the surface. The parts of a rotary vane compressor, on the other hand, are usually fabricated from cast iron, which is porous and retains oil. Lubrication ensures a good contact through which the compressed gas cannot escape. Screw & vane compressors are very popular in South Africa. Should you have any queries regarding this matter, please contact us.