The spiral wound gasket is semi-metallic, comprising of a spirally wound v shaped stainless steel strip and a non-metallic filler material, such as graphite or PTFE. Also on the gasket, is a solid outer ring used for centering and controlling compression. This minimizes the risk of material creep through over-tightening.
For the toughest conditions, spiral wound gaskets are available with an additional inner ring. This protects the windings (particularly the filler), from contamination, or attack by the product travelling past the pipeline joint.
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http://https://www.sealingsupply.com/SPIRAL-WOUND-GASKETS
