Guide Rings and Material Selection
Benefits of Center Ring:
The spiral wound gasket outer centering ring provides the following benefits:
Optimum location between the bolts
Protection of the spiral wound element
Additional security against gasket blow-out
Acts as compression limiter preventing overloading and over compression of the spiral wound element
Prevents radial-flow of soft fillers, 1such as PTFE.
For these reasons it is preferable to use spiral wound gaskets with outer centering rings. The outer ring is marked with nominal size, pressure class, standard and materials.
Benefits of the Inner Ring:
The spiral gasket inner ring provides the following benefits:
Prevents radial-flow of soft fillers, such as PTFE + Graphite
Reduces turbulence-minimising flow resistance
Acts as a heat shield when the spiral wound gasket is subjected to high temperatures.
Inner and outer rings are particularly recommended for use on spiral wound gaskets exceeding class 600lbs, but specifically recommended for high temperatures and pressures to optimise the operational reliability of the spiral wound sealing element. Inner rings are mandatory for PTFE filled spirals.
Material Selection
The material selected for the inner ring and winding metal is usually the same as the flange metal. This prevents corrosion and differential expansion problems. The outer centering ring is generally manufactured from carbon steel with an anti- corrosion treatment. However, the ring may also be manufactured in the same metal as the flange to prevent corrosion problems.
Type 304 Stainless
Type 316 Stainless
Aluminium
Copper
Monel
Steel, Plain
Steel, Zinc Coated
Material Filler Selection
The table below may be used to select the correct filler. It should be pointed out that graphite will be the optimum filler in most cases. Only where graphite could cause media contamination, or is not chemically resistant, should the use of another type of filler material be recommended. In such cases, an alternative solution might be to select a gasket.
Graphite
Graphite is universally chosen because of its good chemical resistance, resistance to ageing, good gas tightness and ability to operate at high temperatures.
PTFE
PTFE is a high quality synthetic material with the following characteristics: excellent chemical resistance, resistance to 260O C, resistant to ageing, excellent gas tightness.
Other Fillers:
Compressed Asbestos Jointing Strips
Asbestos Paper
Grafseal
