Teflon® Encapsulated O-Rings

Another important selection parameter is the construction of the internal elastomer.

Solid-Core Encapsulated O-Rings

A solid core contains elastomer throughout the interior of the O-ring.

Advantages include:

• Higher resistance to compression set
• Stronger recovery force
• More robust sealing under demanding conditions
• Better suitability when reliable energizing force is required

For general industrial sealing, the solid-core design is usually the safer starting point when groove dimensions and assembly force permit it. KODA O-Ring’s product information identifies solid-core construction as its standard configuration and emphasizes its compression-set resistance and recovery characteristics.

Hollow-Core Encapsulated O-Rings

A hollow-core construction contains a circular void within the elastomeric energizer.

This reduces the force required to compress the O-ring.

That characteristic can be valuable when:

• The mating components are relatively fragile
• Assembly force must be minimized
• The gland provides limited compression
• A more compliant seal is required

The trade-off is that a hollow core does not provide exactly the same energizing behavior as a solid core.

If the application has significant pressure, large thermal cycling, or demanding recovery requirements, the solid-core design should normally be evaluated first.

The Most Common Installation Problem: Damaging the Jacket

This is where encapsulated O-rings differ significantly from ordinary rubber O-rings.

The FEP/PFA jacket is much less flexible than a bare elastomer.

A conventional rubber O-ring can tolerate a certain amount of stretching and deformation during installation because the elastomer itself is highly flexible.

An encapsulated O-ring has a relatively rigid outer fluoropolymer layer.

Excessive stretching can therefore cause:

• Jacket deformation
• Surface cracking
• Permanent distortion
• Localized thinning
• Installation cuts
• Leakage after assembly

KODA O-Ring specifically recommends heating encapsulated O-rings before installation and removing sharp edges from installation surfaces.

Recommended Installation Procedure

Step 1: Inspect the O-Ring

Before installation, examine the jacket for:

• Cuts
• Scratches
• Cracks
• Wrinkles
• Flattened areas
• Surface defects

Do not install a seal with visible jacket damage.

Step 2: Inspect the Groove

Clean the groove thoroughly.

Remove:

• Metal chips
• Dirt
• Old seal fragments
• Corrosion products
• Hardened lubricant

The groove must not contain sharp edges that could cut the jacket.

Step 3: Check Assembly Edges

Pay particular attention to:

• Threads
• Keyways
• Ports
• Splines
• Cross holes
• Sharp shoulders

Use an appropriate lead-in chamfer where possible.

Step 4: Warm the O-Ring

Heating increases flexibility and makes installation easier.

One published installation procedure recommends heating the O-rings in water at approximately 100°C / 212°F for at least three minutes, removing them immediately before installation. An oven method using approximately 100°C for at least 15 minutes is also described.

The exact procedure should be adapted to the specific seal construction and manufacturer instructions.

Step 5: Install Without Excessive Stretch

Do not force the O-ring over a sharp edge.

Avoid twisting the ring.

Do not use screwdrivers or other sharp tools to push the seal into position.

Step 6: Allow the Seal to Recover

After installation, verify that the O-ring is correctly seated in the groove before assembling the mating component.

A distorted encapsulated O-ring can create a leakage path even when the dimensional specification is correct.

How to Select the Correct Encapsulated O-Ring

A reliable selection process should follow the application rather than the product catalog.

1. Identify the Fluid

Record:

• Fluid name
• Concentration
• Additives
• Cleaning chemicals
• Contaminants

2. Determine the Temperature

Record both:

• Continuous operating temperature
• Maximum transient temperature

3. Determine Pressure

Include:

• Normal pressure
• Maximum pressure
• Pressure spikes
• Pressure cycling

4. Determine Movement

Is the seal:

• Static
• Reciprocating
• Oscillating
• Rotary

Encapsulated O-rings are most naturally suited to static and carefully engineered dynamic applications. High-speed dynamic applications require additional evaluation because the fluoropolymer jacket has different friction and mechanical behavior from ordinary elastomers.

5. Select the Jacket

Choose between:

FEP → general high chemical resistance

PFA → higher thermal/mechanical demands

6. Select the Core

Consider:

FKM → stronger mechanical recovery and resilience

Silicone → wider low-temperature flexibility and softer sealing behavior

7. Select Solid or Hollow Core

Use:

Solid core → maximum recovery and compression-set resistance

Hollow core → lower compression force and greater compliance

8. Confirm the Standard Size

Common encapsulated O-rings are available in standardized dimensions such as AS568 inch sizes, while metric and custom sizes are also available depending on the manufacturer.

What Information Should Be Included in an RFQ?

Avoid sending a supplier only:

“Need a Teflon O-ring, size 214.”

A technically useful RFQ should specify:

Construction: FEP encapsulated
Core: FKM
Size: AS568-214
Core hardness: Application-dependent / specified requirement
Temperature: ___ °C
Pressure: ___ bar
Media: ___
Static/Dynamic: ___
Quantity: ___
Certification: FDA / USP Class VI / other, if required

This allows the manufacturer to determine whether the requested construction is actually suitable rather than simply supplying a dimensionally correct component.

Important Limitations You Should Know Before Ordering

Encapsulated O-rings are highly capable, but they are not a universal replacement for every elastomeric seal.

Higher Cost

The additional manufacturing process and fluoropolymer material make encapsulated O-rings more expensive than standard NBR or FKM O-rings.

More Difficult Installation

The jacket is less flexible and more vulnerable to installation damage.

Limited Elasticity of the Jacket

The fluoropolymer layer itself does not behave like rubber. The core must provide most of the recovery force.

Core Still Matters

Although the working fluid contacts the jacket rather than the core, core temperature capability, mechanical properties, and compression behavior still determine the overall seal performance.

Groove Design Still Matters

An expensive encapsulated O-ring will not compensate for:

• Excessive extrusion clearance
• Incorrect squeeze
• Poor surface finish
• Sharp gland edges
• Incorrect dimensions

The sealing system must be designed as a whole.

Final Engineering Takeaway

A Teflon® encapsulated O-ring should not be viewed simply as a more expensive version of a conventional O-ring.

It is a two-material sealing system engineered around a specific failure problem.

The fluoropolymer jacket addresses chemical exposure and provides a low-friction, highly resistant sealing surface. The elastomeric core provides the resilience that a solid PTFE seal cannot easily provide. FEP is a strong general choice for aggressive chemical environments, while PFA becomes more attractive as temperature and mechanical demands increase. FKM and silicone cores then allow the engineer to tune the sealing force, resilience, and temperature behavior.

The most important selection principle is therefore:

Do not choose an encapsulated O-ring by size alone. Match the jacket, core, hardness, temperature, pressure, chemical environment, groove geometry, and installation method to the actual operating conditions.

When those variables are correctly matched, FEP- and PFA-encapsulated O-rings can provide a highly reliable solution for chemical processing, pharmaceutical equipment, food machinery, fuel systems, valves, pumps, and other applications where ordinary elastomeric O-rings cannot deliver the required service life.