O-ring 21x3 FPM/FKM Viton - Fluoroelastomer O-ring

Technical Specifications

The Shore A hardness, dimensional tolerances, colour, exact FKM compound, operating temperature range and maximum working pressure are not specified in the product designation.

The use of genuine Viton-branded material has not been independently verified.

What Does O-ring 21x3 FPM/FKM Viton Mean?

The designation identifies the nominal dimensions and elastomer family.

• 21 mm - nominal inside diameter.

• 3 mm - nominal cross-sectional diameter.

• FPM - designation for fluorocarbon rubber used in technical documentation.

• FKM - designation identifying the fluoroelastomer material family.

• Viton - registered trademark associated with specific fluoroelastomer compounds, not a universal name for every FKM product.

The nominal outside diameter is calculated as:

21 + (2 x 3) = 27 mm.

The value of 27 mm is a calculated nominal dimension, not a separately verified measurement of the finished product.

Important: The FPM/FKM designation does not automatically confirm that the O-ring is manufactured from genuine Viton-branded material. Such identification requires supporting manufacturer or material documentation.

Construction and Sealing Principle

The O-ring 21x3 mm FPM/FKM is a continuous elastomeric ring with a circular cross-section.

When installed in a correctly designed sealing groove and compressed between mating surfaces, the elastomer deforms to create contact pressure. This contact pressure helps prevent leakage through the sealed joint.

Sealing effectiveness depends on groove geometry, compression, dimensional tolerances, surface finish, operating pressure and the properties of the FKM compound.

The 3 mm cross-sectional diameter is an essential selection parameter. It should not be replaced with a different cross-section without checking the groove dimensions and required compression.

Properties of FPM/FKM Fluoroelastomer Rubber

FKM fluoroelastomers are widely used in industrial sealing applications involving many oils, fuels, chemicals and elevated operating temperatures.

Typical characteristics include:

• Resistance to many mineral and synthetic oils.

• Resistance to numerous fuels and petroleum-based products.

• Suitability for elevated operating temperatures, depending on the compound.

• Good resistance to ozone and atmospheric ageing.

• Relatively low permeability to many gases compared with certain general-purpose elastomers.

• Limited compatibility with certain ketones, esters, amines and other media, depending on the FKM formulation.

Individual FKM compounds can differ significantly in chemical compatibility, flexibility and long-term sealing performance.

Without material documentation for the specific compound, an exact temperature range or guaranteed resistance to particular chemicals cannot be assigned to this product.

O-ring FPM/FKM Compared with NBR, EPDM and MVQ/VMQ

FKM is not universally suitable for every sealing medium.

Depending on the application, another elastomer may offer better chemical compatibility or mechanical performance.

O-rings made from different materials are not automatically interchangeable, even when their nominal dimensions are identical.

Alternative Designations and Search References

The product may be described using the following alternative designations:

• O-ring 21x3 FPM

• O-ring 21x3 FKM

• FKM O-ring 21x3 mm

• Fluoroelastomer O-ring 21x3

• FPM sealing ring 21x3 mm

• Fluorocarbon rubber O-ring 21x3

• O-ring ID 21 mm CS 3 mm

The term Viton may appear in commercial descriptions of FKM O-rings, but it does not independently establish the origin of the elastomer compound.

These are descriptive variations, not verified manufacturer part numbers or confirmed OEM cross-references.

Selection and Interchangeability

Before selecting the O-ring 21x3 mm FPM/FKM, verify:

• Nominal inside diameter of 21 mm.

• Cross-sectional diameter of 3 mm.

• Sealing groove geometry and dimensional tolerances.

• Required compression of the elastomer.

• Shore A hardness of the supplied compound.

• Operating temperature and pressure.

• Chemical compatibility with the sealed medium.

• Static or dynamic sealing conditions.

• Compression set requirements.

• Risk of extrusion into clearance gaps.

O-rings manufactured from NBR, EPDM or FKM may have identical nominal dimensions but different chemical resistance, mechanical properties and temperature performance.

Matching dimensions alone do not guarantee full interchangeability.

Typical Applications

FKM O-rings may be considered for properly designed sealing arrangements, including:

• Equipment housings and covers.

• Selected oil-handling systems.

• Industrial valves and fittings.

• Certain hydraulic assemblies.

• Industrial components operating with compatible fluids.

These are general applications of FKM sealing materials, not confirmed OEM applications for this specific O-ring 21x3 mm.

Final suitability depends on the actual operating conditions and the specifications of the supplied compound.

Installation and Handling

Before installation, clean the sealing groove and mating surfaces. Remove contamination, burrs and sharp edges that could damage the elastomer.

Install the O-ring evenly without twisting or excessive stretching.

If an assembly lubricant is used, verify its compatibility with the specific FKM compound and the sealed medium.

During storage, protect the sealing ring from contamination, mechanical damage and unnecessary deformation.

FAQ - Frequently Asked Questions

1. What are the dimensions of the O-ring 21x3 FPM/FKM?

The nominal inside diameter is 21 mm, and the cross-sectional diameter is 3 mm. The calculated nominal outside diameter is 27 mm.

2. Are FPM and FKM the same material?

Both designations refer to the fluoroelastomer family. However, individual FKM compounds may have different chemical and mechanical properties.

3. Is the O-ring 21x3 FKM made from genuine Viton?

This cannot be confirmed from the material designation alone. Viton is a registered trademark associated with specific fluoroelastomers, not a universal designation for all FKM compounds.

4. Is the O-ring 21x3 FPM/FKM resistant to oil?

Many FKM compounds offer good resistance to mineral oils and numerous synthetic oils. Compatibility with the specific oil formulation, additives and operating temperature must still be verified.

5. What temperature can the O-ring 21x3 FKM withstand?

The permissible temperature range depends on the compound formulation and operating conditions. Exact minimum and maximum temperatures cannot be reliably specified without material documentation.

6. Can an NBR O-ring 21x3 be replaced with an FKM O-ring?

Not automatically. Identical nominal dimensions do not guarantee chemical compatibility or equivalent mechanical performance.

7. Is the O-ring 21x3 FKM suitable for dynamic sealing applications?

Dynamic sealing requires evaluation of movement speed, friction, lubrication, groove geometry and compound properties. Suitability cannot be confirmed from the FKM designation alone.

8. What is the Shore A hardness of the O-ring 21x3 FPM/FKM?

The Shore A hardness is not specified in the designation and must be confirmed in the technical documentation for the supplied product.

O-ring 21x3 FPM/FKM - Key Information

The O-ring 21x3 mm FPM/FKM is a fluoroelastomer sealing ring with a nominal inside diameter of 21 mm and a cross-sectional diameter of 3 mm. Its calculated nominal outside diameter is 27 mm. FKM materials are commonly selected for resistance to many oils, fuels and elevated temperatures. Exact operating limits depend on the specific elastomer compound.

The product can be sourced through the specialist B2B industrial trading platform simmering.pl, supporting industrial procurement and worldwide shipping from stock in Poland, subject to availability.