Nitrile vs. Viton Gears: How to Choose the Right Gear Material for Your Pump

The Critical Role of Gear Material Selection

While the mechanical design and construction of a pump determine its basic operating characteristics, the elastomer material used in the gear package is the critical determinant of your pump's compatibility with specific fluids, temperature environments, and chemical systems.

In NAPCO pumps, elastomer materials serve multiple functions: they form the sealing surfaces between gear and body, dampen vibration and noise, and influence the overall wear resistance of the pump. Selecting the wrong elastomer for your fluid chemistry can result in accelerated wear, leakage, premature failure, and unplanned downtime.

This technical resource guides you through the properties, performance ranges, and application-specific advantages of the two primary elastomer options available in NAPCO pumps: nitrile rubber (NBR) and Viton (fluoroelastomer, FKM).

Nitrile Rubber (NBR) Gears

Nitrile rubber (nitrile-butadiene rubber, NBR) is a synthetic elastomer combining acrylonitrile and butadiene polymers. It represents the industry-standard elastomer for positive displacement pumps due to its balance of cost-effectiveness, broad chemical compatibility, and reliable performance across moderate operating conditions.

Physical and Chemical Properties

Nitrile exhibits excellent resistance to petroleum-based fluids, mineral oils, water-based emulsions, and moderately aggressive chemicals. The acrylonitrile component of the polymer provides strong hydrocarbon resistance, making nitrile ideal for fuel transfer, mineral oil circulation, and water-based adhesive systems.

Fluid Swell Resistance: Minimal swelling in petroleum-based fluids; excellent dimensional stability in emulsion systems.
Temperature Range: Effective operating range from -20°F to +240°F (standard nitrile formulations), with some extended-range formulations extending to 260°F.
Resilience: Good rebound characteristics; maintains sealing geometry over extended service intervals.
Tear and Abrasion Resistance: Robust mechanical properties; excellent wear resistance in standard industrial applications.
Cost Profile: Most economical elastomer option; enables lower-cost pump configurations.

Chemical Compatibility: Nitrile

Nitrile provides excellent compatibility with fluid families commonly encountered in industrial applications:

Petroleum Products: Mineral oils, hydraulic fluids, crude oil fractions, and refined fuel stocks.
Emulsions: Water-in-oil emulsions (explosives manufacturing), oil-in-water emulsions, and stabilized water-based systems.
Moderate Chemicals: Dilute acids, weak alkalis, glycols, and ester-based solvents at moderate concentrations.
Adhesive Systems: Water-based and latex-based adhesives; thermoset resin systems.

Limitations of Nitrile

Nitrile exhibits degradation or incompatibility with certain fluid families:

Aromatic Solvents: Strong swell and degradation in benzene, toluene, xylene, and related aromatic hydrocarbons.
Chlorinated Solvents: Incompatible with chlorinated hydrocarbons (trichloroethylene, carbon tetrachloride, etc.).
Strong Oxidizers: Attacked by concentrated nitric acid, hydrogen peroxide, and other strong oxidizing agents.
Ozone Degradation: Susceptible to ozone attack; requires protective additives if exposed to ozone-bearing environments.
Very High Temperature: Limited to approximately 240°F; extended high-temperature operation accelerates degradation.

Service Life and Maintenance

In properly selected applications, NAPCO nitrile gear pumps deliver 5,000 to 10,000 operating hours before elastomer replacement becomes necessary. Maintenance is straightforward: elastomer elements are replaced as kits, with gear assemblies remaining serviceable through multiple elastomer change cycles. This modularity is a primary advantage of nitrile pumps in transfer and loading operations where serviceability is critical.

Viton (FKM) Gears

Viton is a fluoroelastomer (fluorine-containing elastomer, FKM) offering superior chemical resistance and extended temperature capabilities compared to nitrile. Viton's exceptional resistance to aromatic solvents, chlorinated compounds, strong oxidizers, and aggressive chemicals makes it the material of choice for demanding chemical processing and specialized industrial applications.

Physical and Chemical Properties

The fluorine atoms incorporated into Viton's polymer backbone provide extraordinary chemical resistance. This molecular structure makes Viton less reactive to aggressive solvents and oxidizers that rapidly attack nitrile elastomers.

Temperature Range: Effective operating range from -10°F to +350°F, with continuous operation possible to 300°F and brief excursions to 400°F.
Chemical Resistance: Superior resistance to aromatic solvents, chlorinated hydrocarbons, strong acids, and oxidizing agents.
Fluid Swell Control: Minimal swelling even in aggressive chemical environments; maintains dimensional stability under extreme fluid exposure.
Ozone and UV Resistance: Excellent resistance to ozone attack and UV degradation; suitable for outdoor and exposed environments.
Resilience and Hardness: Slightly lower rebound than nitrile; requires precision maintenance of clearances and seal geometry.

Chemical Compatibility: Viton

Viton extends compatibility to fluid families that are incompatible with nitrile:

Aromatic Solvents: Excellent resistance to benzene, toluene, xylene, and related aromatics; suitable for solvent-based adhesives and coatings.
Chlorinated Solvents: Compatible with trichloroethylene, perchloroethylene, and other halogenated hydrocarbons.
Strong Acids and Oxidizers: Excellent resistance to concentrated nitric acid, hydrogen peroxide, and similar aggressive oxidizing fluids.
Petroleum Products: Full compatibility with mineral oils, fuel fractions, and standard hydraulic fluids.
High-Temperature Service: Maintains elastomeric properties at elevated temperatures where nitrile degrades.

Limitations of Viton

While Viton's chemical and temperature capabilities are superior, practical considerations limit its selection to applications that genuinely require those advantages:

Cost Premium: Viton elastomer material cost is 50-100% higher than nitrile, increasing pump purchase price.
Maintenance Cost: Elastomer replacement kits are significantly more expensive; service intervals may be longer due to superior durability, but per-service cost is higher.
Low-Temperature Brittleness: Some Viton formulations exhibit reduced flexibility at very low temperatures (below -10°F); nitrile may be preferred for cold environments.
Water Sensitivity: Viton absorbs moisture more readily than nitrile; prolonged exposure to water can affect elastomer properties.

Service Life and Maintenance

In properly specified applications, NAPCO Viton gear pumps can deliver 8,000 to 15,000 operating hours before elastomer replacement is necessary—a 40-50% improvement over nitrile in chemical-intensive applications. The extended service life helps offset the higher material cost in demanding applications where pump downtime is costly.

Detailed Comparison: Nitrile vs. Viton

Property	Nitrile (NBR)	Viton (FKM)
Temperature Range	-20°F to +240°F	-10°F to +350°F
Petroleum Products	Excellent	Excellent
Aromatic Solvents	Poor; rapid swell	Excellent
Chlorinated Solvents	Not recommended	Excellent
Strong Acids	Fair; dilute only	Excellent; concentrated
Strong Oxidizers	Poor; attacked	Excellent
Water-Based Systems	Excellent	Good; may absorb moisture
Ozone Resistance	Fair; requires additives	Excellent
Wear Characteristics	Excellent in compatible fluids	Excellent across wide fluid range
Typical Service Life	5,000-10,000 hours	8,000-15,000 hours
Material Cost	Lower (baseline)	Higher (+50-100%)
Elastomer Replacement Cost	Standard	Higher (+50-75%)
Field Availability	Widely available	Standard; specialty order

Application-Based Selection Guide

The following framework guides gear material selection based on typical application fluids and operating conditions:

Emulsion Explosives (Nitrile Standard)

Water-in-oil and oil-in-water explosives emulsions contain petroleum base stocks, water, sensitizers, and oxidizer salts. This fluid family is completely compatible with nitrile elastomers. Operating temperatures typically remain below 120°F during transfer operations.

Recommendation: NAPCO nitrile pumps (PA300S, PA200S) are optimal for emulsion transfer. The cost-effectiveness of nitrile and its excellent compatibility with water-based emulsions make this selection economical and reliable.

Solvent-Based Adhesives (Consider Viton)

Solvent-based adhesives frequently contain aromatic hydrocarbons (toluene, xylene) as primary solvents. These aromatic compounds cause rapid swelling and degradation of nitrile elastomers. If your adhesive system contains aromatic solvents, nitrile selection will result in premature failure.

Recommendation: Contact NAPCO with your specific adhesive formulation. If aromatic content is above 10%, evaluate Viton pumps for service life and reliability. The higher initial cost may be justified by extended pump life and reduced maintenance frequency.

Water-Based Adhesives (Nitrile Preferred)

Water-based latex and polyvinyl acetate (PVA) adhesives are highly compatible with nitrile elastomers. Operating temperatures are typically moderate (60-120°F), and there are no aggressive chemical constituents.

Recommendation: NAPCO nitrile pumps are the cost-effective choice for water-based adhesive transfer. Viton offers no performance advantage for this application and would represent unnecessary cost premium.

Fuel and Petroleum Transfer (Nitrile Standard)

Gasoline, diesel, crude oil fractions, and refined mineral oils are completely compatible with nitrile elastomers. Aromatic content in these products (naturally present in crude oil) does not cause the same rapid swell as concentrated aromatic solvents; petroleum fractions contain aromatic compounds distributed within a larger aliphatic hydrocarbon matrix.

Recommendation: NAPCO nitrile pumps are appropriate for standard fuel and petroleum transfer. Viton is unnecessary unless the fluid is known to contain concentrated aromatic solvents (benzene, toluene exceeding 50% of composition).

Aggressive Chemicals (Viton Recommended)

Industrial chemical processing involving strong acids (concentrated nitric, sulfuric), chlorinated hydrocarbons, or oxidizing agents demands Viton's superior chemical resistance. These fluids will rapidly attack and degrade nitrile, resulting in leakage and failure.

Recommendation: Specify NAPCO Viton pumps for any application involving concentrated acids, oxidizers, or chlorinated solvents. The higher initial cost is justified by compatible material selection and extended service life.

High-Temperature Service (Viton or Extended-Range Nitrile)

Fluids or operating environments exceeding 240°F exceed the continuous service temperature of standard nitrile. Extended-range nitrile formulations (to 260°F) are available but represent a compromise. Viton's superior high-temperature properties make it the preferred choice for sustained elevated-temperature operation.

Recommendation: For continuous operation above 240°F, specify Viton. Consult NAPCO engineering for temperature profiles and fluid characteristics to confirm Viton selection.

Quick Decision Guide

Does your fluid contain aromatic solvents (toluene, xylene, benzene)?

Yes: Consider Viton; nitrile will swell.
No: Continue evaluation.

Does your fluid contain chlorinated hydrocarbons or strong oxidizers?

Yes: Viton is required; nitrile will degrade.
No: Continue evaluation.

Is operating temperature sustained above 240°F?

Yes: Viton is recommended for extended service life.
No: Nitrile is typically adequate.

Is your application petroleum, water-based adhesives, or emulsions?

Yes: Nitrile is cost-effective and appropriate.
No: Evaluate Viton advantages.

When the Viton Premium Is Justified

Viton's higher material cost can be justified in specific scenarios:

Aggressive Fluid Chemistry: When nitrile is incompatible, Viton is the only viable option; cost comparison is irrelevant.
Extended Service Intervals: When Viton's longer service life (40-50% improvement) reduces maintenance frequency, the higher cost per service may be acceptable.
Critical Downtime Impact: When equipment downtime is costly, Viton's improved reliability justifies the premium investment.
High-Temperature Continuous Operation: When your application demands sustained operation above 260°F, Viton is the only practical choice.

Develop a total cost of ownership calculation specific to your operation, incorporating equipment cost, elastomer replacement frequency, service interval, and downtime impact.

Related Technical Resources

Need Help Choosing the Right Gear Material?

Contact NAPCO with your fluid chemistry, operating temperature, and expected service interval. Our engineering team will recommend the optimal gear material for your application.

Contact NAPCO Engineering