Sedifilt - Syntech Fibres (Pvt)

Continuous fibres lead to successfuI filter

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Courtesy of Sedifilt - Syntech Fibres (Pvt)

An improved design of wound string filter has doubled contaminant holding capacity and avoided the shedding of small fibres bad into the fluid. Tom Shelley investigates

Wound string filters are setting new benchmarks for efficiently catching large amounts of dirt, without risk of introducing stray fibres or other contaminants into the fluid stream being filtered.

Initially made of melt spun polypropylene for the filtration of water, the filters are now also available in polyester and other materials and are finding their way into oil and gas applications. The manufacturer responsible for the filter is Syntech fibres in Pakistan, which started out as a producer of polypropylene textiles. Director Hamid Omar told Eureka during a recent visit, that moving from the competitive synthetic textile business into manufacturing and engineering was 'a business breakthrough' and the firm is now focussing its entire efforts on making filters.

The innovative, patent-pending 'Sedifilt' device is a wound filter, with the yam made up from continuous filaments. Rather than being round, the filaments are multi-lobed, which ensures a higher dirt holding capacity and lower resistance to flow. The filaments are randomly oriented to each other, intermixed, looped and entwined to produce a bulky yam. When wound into a cartridge, each filament continues, without d break, throughout 'he length of the yam. During winding, the pitch, number of crossings and space between each yarn is continuously varied so that the inner layers are close wound, while the outer layers are more open, but using the same winding tension. Each yam traps the randomly protruding short loops of adjacent yams to yield a stable structure.

The diamond-shaped voids normally found in conventional wound string filters are avoided, and there are no short fibres that can break away as loose bits. Dirt holding capacity and filter life is said to be about double that of conventional wound filters and pressure drop is halved.

The favoured material is polypropylene, melt spun without using lubricants, wetting agents, emulsifiers, antioxidants or antistatic agents. Polyester media filter cartridges with stainless steel cores are available for high temperature applications. The filters are suitable for: reverse osmosis pre-treatment and filtering drinking water; beverages; gases; electronic, electroplating and photographic solutions; deep well injection of processed water for oil and gas; waste water disposal and cooling towers.

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