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A completely different constructed cartridge has a perforated cylindrical core around which is wound a continuous filament or yarn. With a plastic filament or metal wire, the core may be threaded and the first layer of the filament is wound into the threads, giving the required degree of spacing of consecutive turns. The cartridge may have just one layer, when the effect is the same as an edge filter, or there may be several layers, which are usually at opposite angles, layer by layer, to give a component of depth filtration.

More commonly, a multifilament or staple yarn is used. This kind of cartridge is constructed by continuously winding the yarn in a carefully controlled open pattern around the central core, which is typically a perforated metal or plastic tube open
at each end. Typically the matrix so formed has a graded structure with pores of decreasing size meeting the inward direction of flow – a gradation achieved by differing degrees of tightness in the windings. Cartridges are based on a wide variety of yarn materials embracing both natural and synthetic fibres. The yarns used are mostly spun from short staple fibres, the fibrillated surface of which is brushed or teased to produce a fuzzy surface or nap, which contributes importantly to the filtration mechanisms. If monofilament yarns are used, they are generally texturized or crimped in some fashion before being formed into a cartridge.

Despite its early origin, in the 1930s, the 63mm diameter X 250 mm long yarn-wound cartridge continues to be widely used in many sectors of industry. Its simple construction, and its convenient versatility in use, resulted in its becoming an unofficial standard as increasing numbers of manufacturers competed for a large and growing market. It also effectively served as a prototype in respect of size and dimensions for the diversity of styles of cartridge developed in more recent years.

The filtration characteristics of a yarn-wound cartridge depend on the type of yarn used as well as on the way it is produced and wound. Filtration within the interstices of the yarn is as important a mechanism as filtration in the spaces between the consecutive turns.

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