What is a spiral wound gasket?

The sealing portion of the spiral wound gasket consists of alternating layers of metal and non-metallic (Graphite or PTFE) strips wrapped in a tight spiral. The non-metallic material helps form the seal and the metal reinforces it and gives it rigidity. ASME B16.20 spiral wound gaskets should have an inner and outer solid metal ring. These rings serve multiple purposes (avoid over-compression, buckling, and blow-out and unraveling of the spiral wound section).