Media classification, filters

Various types of filter media and the materials oi which they are constructed are surveyed extensively by Purchas Industrial Filtration of Liquids, CRC Press, Cleveland, 1967, chap. 3), and characterizing measurements (e.g., pore size, permeabihty) are reviewed in detail by Rushton and Griffiths (in Orr, op. cit., chap. 3). Briefer summaries of classification of media and of practical criteria for the selec tion of a filter medium are presented by Shoemaker (op. cit., p. 26) and Purchas [Filtr Sep., 17, 253, 372 (1980)]. 

A vast variety of materials in diverse forms are used as filter media for which Purchas (1981) produced a guideline classification, which is reproduced in Table 2.1. Alternative methods of classification are available, but there always exist media that cannot be fitted neatly into the classification scheme. For example, Flood et al (1966) classified filter media into surface and depth media types. Surface type media are distinguished by the fact that the particles in suspension are mostly retained on the surface of the medium, with little penetration into the pores. Examples are filter paper, filter cloths and wire mesh. Depth type media, used mainly for liquid clarification, are characterised by the fact that the particles penetrate into the pores, where they are retained. The pores of such media are considerably larger than the sizes of the particles in... 

Cartridges are available in a very wide range of types, and in almost every type of filter medium. However they can be broadly classed into two types, according to their construction, which can easily be distinguished, although even here there are formats that bridge this classification. The first uses an integral piece of porous... 

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