ring blowers are suitable for all those applications requiring considerably higher pressures than that which can be achieved using centrifugal fans. Side channel exhausters are used in all those applications requiring an operating vacuum higher than the one achievable by a fan, but not as high as to require the use of a vacuum pump. The rotating parts are not in contact with the casing. There is therefore no friction during operation and thus no internal lubrication is necessary. The gas moving through the machine therefore remains uncontaminated and completely oil-free.