What Is an Encapsulated O-Ring?

O-rings by Monroe Engineering

O-rings are essential to protecting machinery parts from leaking. They consist of a donut-shaped seal that’s placed between the mating surface of two parts. With an O-ring, fluids and gases can travel between the two parts without leaking. Some O-rings, however, are encapsulated. What is an encapsulated O-ring exactly, and how does it differ from other types of O-rings?

The Basics of Encapsulated O-Rings

An encapsulated O-ring is a type of donut-shaped mechanical seal that’s characterized by the use of two components. Encapsulated O-rings feature an inner core and an outer jacket. The inner core is designed to give encapsulated O-rings “memory.” In other words, it allows them to revert back to their original shape and size after expanding.

Other types of O-rings, conversely, typically consist of a single component. They are made of a single and solid piece of material. Encapsulated O-rings are different in the sense that they are made of two components. All encapsulated O-rings have an inner core and an outer jacket. The outer jacket wraps around the inner core. They are known as “encapsulated O-rings” because the outer jacket “encapsulates” the inner core.

FEP vs PFA Jackets

The jacket used in encapsulated O-rings is typically made of polytetrafluoroethylene (PTFE). PTFE, of course, is a fluoropolymer of tetrafluoroethylene. It’s a strong yet elastic synthetic material that offers a high level of protection against leaks — even when exposed to heat and pressure. With that said, PTFE is available in different grades, two of the most common being FEP and PFA.

Some encapsulated O-rings feature FEP PTFE, whereas others feature PFA PTFE. Both types of jackets offer their own advantages. FEP jackets, for instance, are highly versatile and offer excellent corrosion resistant properties. PFA jackets, on the other hand, are typically able to withstand more heat.

Inner Core Materials

While the jackets in encapsulated O-rings are typically made of PTFE, the inner cores are made of other materials. You can find encapsulated O-rings with different types of inner core materials. Some of them are made of silicone, for instance. Silicone inner cores are strong, elastic and resistant to both heat and pressure.

Some encapsulated O-rings have an inner core made of a fluoroelastomer compounds. It’s a more advanced material that provides excellent recovery from deformation. All encapsulated O-rings will deform when exposed to heat and pressure. They’ll typically deform by expanding. Those with a fluoroelastomer inner core, however, will recover more quickly from this deformation.

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