How to Choose the Right Elastomer Material (NBR, EPDM, Viton) for Bellow Shaft Seals

Introduction

Mechanical seals are the backbone of modern pump technology, ensuring reliable fluid containment and efficient operation across industries. Among the various seal types, elastomer bellow shaft seals stand out for their simplicity, flexibility, and cost-effectiveness.

However, the performance of elastomer bellow shaft seals depends heavily on the elastomer material used in the bellows. Common options include NBR (Buna-N), EPDM, and Viton (FKM). Each has unique chemical and physical properties that make it suitable for specific applications.

As a professional manufacturer and exporter of mechanical seals, Wecan Seals leverages its in-house production system to provide customized elastomer bellow shaft seals tailored to different industries. This article explores the differences between NBR, EPDM, and Viton, and provides a guide on how to choose the right material for your sealing needs.

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Understanding Elastomer Bellow Shaft Seals

Elastomer bellow shaft seals are single spring mechanical seals where the bellows act as both a secondary sealing element and a flexible compensator. The elastomer material allows the seal to adapt to shaft misalignment, vibration, and axial movement while maintaining a tight seal.

The key role of the elastomer is to:

Maintain fluid-tight sealing around the shaft
Provide flexibility and shock absorption
Ensure compatibility with operating fluids

Therefore, selecting the correct elastomer material is critical to performance, reliability, and cost efficiency.

The Three Most Common Elastomer Materials

1. NBR (Buna-N)

Full Name: Nitrile Butadiene Rubber
Temperature Range: -20°C to +120°C
Key Properties:

Excellent resistance to oils, fuels, and non-polar solvents
Good abrasion resistance
Economical and widely available

Limitations:

Limited resistance to ozone, weathering, and polar solvents
Not ideal for high-temperature or highly aggressive chemicals

Best Applications:

Automotive water and oil pumps
Light industrial pumps
General-purpose sealing in oil-lubricated systems

2. EPDM (Ethylene Propylene Diene Monomer)

Temperature Range: -40°C to +150°C
Key Properties:

Excellent resistance to water, steam, and polar chemicals
Superior weather, ozone, and UV resistance
Good flexibility across a wide temperature range

Limitations:

Poor resistance to oils, fuels, and hydrocarbons
Not recommended for pump systems with oil-based fluids

Best Applications:

Water treatment plants
HVAC and chiller systems
Pumps handling hot water, steam, and mild chemicals

3. Viton (FKM)

Full Name: Fluoroelastomer (commonly known as Viton®)
Temperature Range: -20°C to +200°C (with some grades up to +250°C)
Key Properties:

Exceptional resistance to aggressive chemicals, acids, and hydrocarbons
Excellent high-temperature performance
Low gas permeability, making it ideal for vacuum and gas sealing

Limitations:

Higher cost compared to NBR and EPDM
Slightly less flexible at very low temperatures

Best Applications:

Chemical processing plants
Oil & gas pumps
High-temperature industrial applications

Comparison Table: NBR vs EPDM vs Viton

Feature	NBR (Buna-N)	EPDM	Viton (FKM)
Temperature Range	-20°C to +120°C	-40°C to +150°C	-20°C to +200°C
Chemical Resistance	Oils, fuels	Water, steam, polar fluids	Aggressive chemicals, hydrocarbons
Weather/Ozone Resistance	Poor	Excellent	Good
Cost	Low	Moderate	High
Applications	Automotive, general pumps	HVAC, water treatment	Chemical, oil & gas, high temp