In order to achieve the smallest residual oil content in compressed air, filters with stepped separating qualities were developed. For this, microfibre has proved of value, particularly in the range of fine separators. With 95% porosity (voids volume), this offers not only adequate space for the air flowing through and, therefore, a low pressure loss, but also voids of the largest possible size for the oil droplets to be retained. The relatively unstable microfibre is supported on the inside and outside through perforated stainless steel cylinders. A coarser fibre layer fitted immediately upstream protects the microfibre from gross pollution and therefore preserves the filtering qualities. For filtration and for the analysis of systems dispersed in air, filters from fine organic and inorganic fibres can now be regarded as the most effective filtering material. They are characterised by high separating efficiency at low differential pressure. The individual fibres of a are mutually arranged in a labyrinth and thus subject the continuous carrying phase of throughflow to innumerable subdivisions. In contrast to a woven filter with systematic structure, the dispersed particles impinge much more frequently on a fibre so that the probability of retention is higher. Moreover, microfibre filters display a 30% lower pressure loss than woven filters at the same efficiency of separation.
