Encapsulated o-rings are specialty seals designed for use in applications where high temperature and corrosive conditions make the use of traditional elastomer o-rings infeasible.
The o-rings are comprised of two parts: a rubber inner core, which provides compression and elasticity, and a thin outer jacket made from Teflon®, which gives the seal high corrosion resistance and thermal stability. They are widely used in chemical, petrochemical, food, and pharmaceutical processes, where seals are required to perform reliably in extremely harsh environments.
Depending on core material, encapsulated o-rings are suitable for operating temperatures ranging from -62° to +204°C (-80° to +400° F). They resist almost all chemicals and retain their mechanical properties, even during extended exposure to high-temperature environments. They also possess excellent dielectric properties, a low coefficient of friction, flexibility, toughness, and negligible moisture absorption.
Encapsulated o-rings are available in two different core types: solid core and hollow core.
Solid Core – Standard encapsulated o-rings are supplied with either solid Viton® / FKM or silicone energizers. Viton offers excellent elastic qualities and compression set. Silicon offers many of the same advantages, however, because it is softer than Viton, it exhibits higher thermal resistance. Encapsulated o-rings with silicon cores also provide better flexibility in cold temperatures.
Both Viton and silicone core encapsulated o-rings comply with Part 177 of Title 21 of the Food and Drug Administration regulations for producing, manufacturing, processing, preparing, treating, packing, transporting, and holding food.
Hollow Core – While solid core energizers provide the highest resistance to compression set and recovery, hollow core encapsulated o-rings are ideal in fragile applications where extreme elasticity is required for effective sealing.
The outer jacket of encapsulated o-rings can be made from one of two materials: FEP or PFA.
FEP (fluorinated ethylene propylene) – FEP jacketed o-rings offer excellent resistance to a broad range of corrosive chemicals, including alcohols, aromatic solvents, naptha, acids, and petroleum spirits. They also have a low compression set and coefficient of friction. The operating temperature range of encapsulated o-rings with FEP jackets is -60°C to +205°C (-76°F to +400°F). The o-rings are FDA, USP CLASS VI, and SANITARY 3A compliant.
PFA (perfluoroalkoxy-copolymer) – PFA possesses many of the same properties as FEP. However, it does exhibit higher mechanical strength and better resistance to stress and cracking. Encapsulated o-rings with PFA jackets are typically used in applications where extreme thermal stability and durability are required. They are suitable for use in operating temperatures ranging from -60°C to +260°C. (-76°F to 500°F) and typically have a longer service life.
Encapsulated O-Ring Limitations
Although encapsulated o-rings possess a number of properties that make them advantageous in harsh process environments, there are instances where they may not be ideal for use. This is particularly true in applications where the o-ring will be exposed to abrasive substances, such as powders or slurries, as the thin outer jacket can easily be damaged.
Additionally, because the outer FEP/PFA jacket is not as compressible as the Viton / silicone core, it should not be used in situations where it will be subject to extreme stretching or squeezing. Because of this, care should be taken during installation to ensure that the o-ring is set properly in the bore and that the outer jacket has not been kinked.
In general, solid core encapsulated o-rings are ideally suited for static use; however, they can be utilized in some slow-moving rotatory applications for valve stem sealing.
The Right Encapsulated O-Ring is Application-Specific
Choosing the proper encapsulated o-ring will largely depend on the specific needs of the application. Global O-Ring and Seal carries a full line of encapsulated o-rings in all AS568 standard sizes. Custom sizes are available upon request — as are o-rings with rectangular, oval, and square cross-sectional profiles.
If you’re a distributor or end-user of o-rings and may have a need for our services, contact us today to speak with one of our technical sales professionals or order online from our extensive inventory.