The spiral wound gasket depends upon the mechanical characteristics of a formed metal spiral strip, rather than the compressive virtues of more traditional gasket materials. This makes it particularly suitable for low or fluctuating bolt loads. The sealing strips, or fillers, are usually graphite, although other materials such as PTFE may be used, the windings are always s/steal. For this type of gasket to work the spiral must not be over compressed, hence one of two types of compression control is usually used.
The completed gasket is fitted into a steel ring of specific thickness. When the gasket is fitted into a flange and the bolt load is applied, flange closure is governed by the outer steel ring of the gasket. To further improve the pressure rating of the spiral wound gasket, a steel ring may be added to the inside. This also protects the windings (particularly the filler) , from contamination, or attack by, the product.
The second usually compression control is not fitted to the gasket at all, but engineered into the flange. These Gaskets are called Unsupported Spiral Wound Gaskets.
METAL WINDING STRIP
GUIDE RING MATERIALS