FEP type PTFE Fluoropolymers (performance plastics) offer excellent chemical and temperature resistance, but lack the resiliency of elastomers (rubber) required to maintain a quality seal. Encapsulated and spring energized seals combine the best sealing features of plastics, elastomers and steel springs to increase chemical and temperature performance compared to most solid elastomers. The main offsetting limitation is PTFE's stiffness that can require custom gland design to maximize sealing by using the right amount of compression force to maintain a seal without over compressing which can shorten seal life. PFA type PTFE is also available for additional upper temperature resistance (up to +575° F short exposure) but not widely used due to reduced sealing performance.
FKM or silicone is used as the material for the core of the encapsulated O-ring. EPDM is not recommended due to heat-related changes during the manufacturing process. FKM and silicone withstand these temperatures during production without a decline in performance.
FKM core – FKM (black) features very good rubber-elastic qualities. FKM has the capacity to re-assume its original form after its deformation thanks to its outstanding compression
Silicone core – The silicone core (mostly red) is considerably softer than an FKM core. In turn, it is more temperatureresistant. In addition to its superb thermal resistance, it has very good cold flexibility.
FEP encapsulation – FEP (fluorinated ethylene propylene) gives an O-ring its tremendous characteristics relating to its resistance to nearly all liquids, gases and chemicals. The exceptions are liquid alkali metals and some fluorine compounds.
PFA encapsulation – Perfluoroalkoxy copolymer (PFA) resembles FEP in its areas of application. It is distinguished by improved cold flow properties and optimized mechanical
qualities at higher temperatures.
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