O-ring FPM 38x4 FKM Viton

Product Description

O-ring FPM 38x4 FKM Viton is a circular cross-section sealing ring made from fluorocarbon rubber (FPM/FKM), with a nominal inside diameter of 38 mm and a cross-section diameter of 4 mm. Its calculated nominal outside diameter is 46 mm. This fluoroelastomer O-ring is primarily intended for static sealing applications requiring compatibility with many mineral oils, fuels, lubricants and selected chemical media.

The 38x4 mm O-ring provides sealing through controlled elastic deformation between mating surfaces. When installed in a correctly designed groove, the elastomer is compressed and generates contact pressure that helps prevent fluid or gas leakage.

FKM fluoroelastomers are widely used in sealing applications involving demanding chemical environments and elevated operating temperatures. Compared with standard NBR rubber, FKM often provides better resistance to heat, many petroleum-based products and selected chemicals.

FPM and FKM are different designations for the same general family of fluorocarbon elastomers. Viton, however, is a registered trademark for specific fluoroelastomer materials. The designation FKM alone does not confirm that a particular O-ring is manufactured from genuine Viton-branded material.

Technical Specifications - O-ring FPM 38x4 FKM Viton

The nominal outside diameter of 46 mm is calculated from the inside diameter and twice the cross-section diameter.

Actual manufactured dimensions are subject to the applicable dimensional tolerances.

The exact Shore A hardness, temperature limits, pressure rating, compound formulation and chemical compatibility cannot be established from the designation FPM 38x4 alone.

These properties must be confirmed for the specific FKM compound supplied.

What Does O-ring FPM 38x4 FKM Viton Mean?

O-ring - Circular Sealing Ring

An O-ring is a closed elastomeric sealing element with a circular cross-section.

Its function is to prevent or reduce leakage between mating components when installed in a properly designed sealing groove.

O-rings are used in both static and selected dynamic applications, depending on material properties and operating conditions.

FPM - Fluorocarbon Rubber

FPM is a European material designation for fluorocarbon elastomers.

These materials are commonly used in industrial sealing applications requiring resistance to many oils, fuels, lubricants and elevated temperatures.

The designation identifies a material family rather than a specific compound formulation.

38 - Inside Diameter

The number 38 indicates the nominal inside diameter of the O-ring in millimetres.

For this product, the inside diameter is 38 mm.

This is one of the two principal dimensions used to identify an O-ring.

4 - Cross-Section Diameter

The number 4 indicates the nominal cross-section diameter of 4 mm.

The cross-section determines how the sealing ring fits into the groove and influences the amount of compression during installation.

Correct compression is essential for reliable sealing performance.

FKM - Fluoroelastomer Material

FKM is the material designation used in ASTM nomenclature for a family of fluorocarbon elastomers.

FPM and FKM refer to the same general material category.

However, individual FKM compounds may differ in fluorine content, chemical formulation, hardness, low-temperature flexibility and chemical resistance.

Viton - Fluoroelastomer Trade Name

Viton is a registered trademark associated with specific fluoroelastomer materials.

The term is frequently used when searching for FKM sealing products.

However, not every FKM O-ring is manufactured from genuine Viton-branded material.

Confirmation of the exact material origin requires documentation from the manufacturer or supplier.

O-ring FPM 38x4 mm Dimensions

The nominal outside diameter is calculated using the following relationship:

Outside diameter = Inside diameter + 2 x Cross-section diameter

For the 38x4 mm O-ring:

38 + 4 + 4 = 46 mm.

Therefore, the nominal dimensions are:

• Inside diameter: 38 mm.

• Cross-section diameter: 4 mm.

• Outside diameter: 46 mm.

The dimensions 38x4 mm describe the O-ring itself, not the recommended groove dimensions.

Groove width, groove depth, compression and installation clearances must be selected according to the sealing arrangement and operating conditions.

Construction and Sealing Principle

The FPM 38x4 mm O-ring is an elastomeric ring with a circular cross-section.

Unlike mechanical seals with multiple components, an O-ring provides sealing through the elastic deformation of its material.

When installed in a properly dimensioned groove, the ring is compressed between the mating surfaces.

This compression creates contact pressure that helps restrict the passage of liquids or gases.

The effectiveness of the seal depends on:

• Correct groove geometry.

• Appropriate O-ring compression.

• Elastomer hardness and elasticity.

• Operating pressure.

• Operating temperature.

• Chemical compatibility with the sealed medium.

• Surface finish of mating components.

• Compression set and material ageing.

• Static or dynamic operating conditions.

In dynamic applications, additional factors include friction, movement speed, lubrication and wear.

A 38x4 mm O-ring should not be selected solely on the basis of its nominal outside diameter.

FPM / FKM Material Properties

Fluorocarbon elastomers are used in industrial sealing technology because of their resistance to many petroleum-based fluids, selected chemicals and elevated temperatures.

Resistance to Mineral Oils and Lubricants

FKM generally offers good resistance to many mineral oils and industrial lubricating greases.

This makes the material suitable for consideration in sealing systems involving compatible lubricants and petroleum-based fluids.

However, compatibility with a particular synthetic oil, additive package or industrial lubricant must be verified separately.

Fuel Resistance

Many FKM compounds provide good resistance to hydrocarbon-based fuels.

Their performance depends on the fuel composition, additives, operating temperature and exposure conditions.

Compatibility with fuels containing alcohols or other components should be checked for the specific compound.

Chemical Resistance

FKM is resistant to many hydrocarbons and selected industrial chemicals.

However, it is not universally compatible with all chemical substances.

Standard FKM compounds may have limited resistance to ketones, amines, certain glycol-based fluids and hot water or steam.

The correct material should always be selected using chemical compatibility information relevant to the specific compound and operating conditions.

Temperature Resistance

FKM materials are frequently selected for applications requiring higher temperature resistance than standard NBR compounds.

However, there is no single temperature range that applies to every FKM O-ring.

Permissible operating temperatures depend on the compound formulation, exposure time, sealed medium and mechanical operating conditions.

For this reason, no unverified minimum or maximum temperature rating is assigned to this particular product.

Ageing and Ozone Resistance

FKM generally provides good resistance to ozone and many environmental factors associated with elastomer ageing.

Nevertheless, sealing performance can deteriorate over time because of chemical exposure, heat, mechanical deformation and compression set.

FKM vs NBR vs EPDM O-rings

This comparison describes general material-family characteristics rather than guaranteed specifications for an individual O-ring.

An FKM 38x4 mm O-ring and an NBR 38x4 mm O-ring have the same nominal dimensions but are not automatically interchangeable.

The material must be selected according to the sealed medium, temperature, pressure and operating requirements.

O-ring FPM 38x4 vs Other Dimensions

These values are dimensional comparisons, not confirmed replacement references.

Changing the cross-section from 4 mm to 3.5 mm affects the amount of compression within the groove.

Changing the inside diameter from 38 mm to 40 mm affects the fit of the sealing ring.

Different dimensions should not be substituted without verifying the sealing groove and the required dimensional tolerances.

Alternative Designations and Search References

The product may also be identified using the following terminology:

• O-ring FPM 38x4 FKM Viton

• O-ring FPM 38x4

• O-ring FKM 38x4

• FPM O-ring 38x4 mm

• FKM O-ring 38x4 mm

• Fluorocarbon O-ring 38x4 mm

• Fluoroelastomer sealing ring 38x4 mm

• FKM rubber seal 38x4 mm

These are alternative descriptive designations, not separate manufacturer part numbers.

No unverified OEM references or manufacturer-specific cross-reference numbers have been assigned.

The term Viton is retained as part of the supplied commercial product name, without independently confirming the origin of the specific FKM compound.

How to Select the Correct FKM 38x4 O-ring

Before ordering, verify the following technical requirements:

1. Inside diameter: 38 mm.

2. Cross-section diameter: 4 mm.

3. Material family: FPM / FKM.

4. Required hardness: appropriate Shore A value.

5. Sealed medium: chemical compatibility with the elastomer.

6. Operating temperature: within the verified limits of the compound.

7. Operating pressure: compatible with the seal design.

8. Application type: static or dynamic.

9. Groove dimensions: suitable width, depth and clearances.

10. Dimensional tolerances: compatible with the sealing arrangement.

11. Surface finish: appropriate for the application.

12. Material approvals: where required by the equipment or industry.

For high-pressure applications, the risk of elastomer extrusion into the installation clearance must also be considered.

Depending on the sealing design, a backup ring may be required.

Two FKM O-rings with identical dimensions can have different hardness values, chemical resistance and low-temperature properties.

Therefore, dimensional compatibility alone does not guarantee complete interchangeability.

Typical Applications of FKM O-rings

FKM O-rings are used in appropriately designed sealing systems where the operating medium is compatible with fluorocarbon elastomers.

Typical application categories include:

• Hydraulic systems using compatible fluids.

• Industrial valves and fittings.

• Pump assemblies.

• Mechanical housings.

• Flanged connections.

• Industrial lubrication systems.

• Fuel handling equipment, subject to material compatibility.

• Industrial equipment exposed to selected chemical substances.

These are general applications of FKM sealing materials.

They do not constitute verified OEM applications for the specific 38x4 mm O-ring.

Installation and Maintenance

Preparation

Before installation, clean the sealing groove and mating surfaces.

Remove dirt, metal particles and other contaminants that could damage the elastomer or compromise sealing performance.

Groove Inspection

Inspect the groove for sharp edges, burrs and surface damage.

The groove geometry must be appropriate for the O-ring dimensions, material hardness and operating conditions.

O-ring Installation

Avoid twisting, cutting or excessively stretching the O-ring during installation.

Use suitable installation tools where necessary.

Lubrication During Assembly

If an assembly lubricant is used, it must be chemically compatible with the FKM material and the sealed medium.

Do not assume that every lubricant is suitable for every fluoroelastomer compound.

Inspection After Assembly

After installation, verify that the sealing ring is correctly positioned and has not been pinched or displaced.

Leak testing should be performed according to the requirements of the equipment and application.

Storage

Store O-rings in a clean, dry environment away from direct sunlight, excessive heat and incompatible chemicals.

Avoid prolonged deformation during storage.

Frequently Asked Questions - O-ring FPM 38x4 FKM Viton

1. What are the dimensions of the FPM 38x4 O-ring?

The nominal inside diameter is 38 mm, the cross-section diameter is 4 mm and the calculated nominal outside diameter is 46 mm.

2. Are FPM and FKM the same material?

Yes. FPM and FKM are designations for the same general family of fluorocarbon elastomers. Individual compounds may have different technical properties.

3. Is every FKM O-ring made from genuine Viton?

No. Viton is a registered trademark for specific fluoroelastomer materials. The designation FKM alone does not confirm that the O-ring is manufactured from genuine Viton-branded material.

4. Is an FKM 38x4 O-ring suitable for hydraulic oil?

FKM generally provides good resistance to many mineral-based hydraulic oils. Compatibility with the specific hydraulic fluid, particularly synthetic or fire-resistant formulations, must be verified.

5. Can an FKM O-ring withstand high temperatures?

FKM materials often provide better high-temperature resistance than standard NBR. However, the permissible temperature range depends on the exact compound and operating conditions.

6. Can a 38x4 mm O-ring be replaced with a 38x3.5 mm O-ring?

Not without checking the sealing groove. A smaller cross-section changes the compression of the sealing ring and may reduce sealing effectiveness.

7. What is the Shore A hardness of the FPM 38x4 O-ring?

The hardness cannot be reliably determined from the dimensions and FPM designation alone. The specific Shore A value must be confirmed in the product's material specification.

8. Can the FKM 38x4 O-ring be used in dynamic sealing applications?

Yes, provided that the sealing system is designed for dynamic operation and the compound is suitable for the movement speed, friction, lubrication, pressure and temperature conditions.

O-ring FPM 38x4 FKM Viton - Key Information

O-ring FPM 38x4 FKM Viton is a fluorocarbon rubber sealing ring with a nominal inside diameter of 38 mm and a 4 mm cross-section. Its calculated outside diameter is 46 mm. FPM and FKM identify the same elastomer family, offering resistance to many oils and fuels. Selection requires verification of compound hardness, chemical compatibility and operating conditions.

FPM/FKM O-rings are offered by simmering.pl, a specialist supplier of industrial sealing components and technical spare parts. The company operates a warehouse in Lublin, Poland, providing stock in Poland and worldwide shipping options for international customers.