Why Rotary Gear Pumps Excel in Chemical Transfer
Chemical transfer operations demand pumps that deliver consistent, predictable flow rates without pulsation or shear, while resisting corrosive attack from acids, solvents, oxidizers, and alkaline solutions. Rotary gear pumps are engineered for this demanding duty.
Positive displacement gear pumps provide several advantages over alternative designs for chemical service:
- Consistent Flow Rate: Flow depends only on pump displacement and RPM, independent of downstream pressure variations or fluid viscosity changes.
- No Pulsation: Unlike vane or centrifugal pumps, gear pumps deliver smooth, steady flow ideal for precision dispensing and metering applications.
- Positive Displacement: Mechanical gear action ensures all fluid is moved forward; no slipping back through impellers.
- Minimal Turbulence: Laminar flow pattern reduces shear degradation of chemically sensitive formulations.
- Field-Serviceable Design: Repair kits enable on-site rebuild without factory return, minimizing downtime in chemical plants.
Understanding Chemical Attack: What Damages Pump Materials
Not all chemicals are equally corrosive to pump metals. Standard ductile iron construction is adequate for many industrial fluids but will fail rapidly in aggressive chemical environments. Stainless steel provides superior resistance, but seal material selection is equally critical.
Classes of Chemical Attack
Strong Mineral Acids: Hydrochloric acid, sulfuric acid, and nitric acid attack ductile iron housing rapidly, penetrating even paint coatings. These applications require full stainless steel construction (housing, shaft, end covers all stainless).
Oxidizing Agents: Chlorine, hydrogen peroxide, permanganates, and other oxidizers initiate galvanic corrosion in ductile iron. The ductile iron matrix oxidizes preferentially, creating pitting and loss of structural integrity. Stainless steel resists oxidizing attack through passive film formation.
Aromatic Solvents: Benzene, toluene, xylene, and other aromatic compounds swell and degrade nitrile rubber seals. These applications require Viton elastomers regardless of housing material.
Chlorinated Hydrocarbons: Chloroform, carbon tetrachloride, and chlorinated solvents attack both nitrile and some Viton formulations. Extreme compatibility testing is essential; consult NAPCO engineering for uncertain applications.
Alkaline Solutions: Sodium hydroxide and potassium hydroxide attack aluminum and some copper alloys but are generally compatible with stainless steel and ductile iron. Nitrile and Viton are both suitable for alkaline service.
Stainless Steel Construction: Full Wetted Path Protection
NAPCO chemical transfer pumps feature 304 or 316 stainless steel construction in all wetted components: housing, internal shaft, end covers, and wear plates. This complete stainless steel design eliminates the galvanic couple that would form between stainless components and ductile iron, ensuring uniform corrosion resistance.
304 vs. 316 Stainless Steel
304 Stainless Steel: The standard choice for most chemical applications. 304 provides excellent corrosion resistance to organic acids, mild mineral acids, and alkaline solutions. Molybdenum content is minimal (0%), making 304 less resistant to chloride attack.
Select 304 for: Typical chemical processing, organic acids, alkaline solutions, non-chloride environments.
316 Stainless Steel: Enhanced composition includes 2-3% molybdenum, providing superior resistance to chlorides and pitting corrosion. 316 is essential for coastal or marine environments and applications involving chloride-containing chemicals.
Select 316 for: Chloride-containing environments, coastal installations, strong mineral acids with chloride salts, or applications requiring maximum pitting resistance.
Shaft Material in Stainless Pumps
NAPCO stainless pumps specify stainless steel shafts (typically 420 stainless or equivalent) rather than carbon steel shafts. This eliminates a potential corrosion pathway and ensures the wetted surfaces remain consistently stainless steel, preventing localized galvanic attack.
Seal Materials for Aggressive Chemical Service
All NAPCO pumps use primary and secondary seals (high-pressure and low-pressure seals) to contain the pumped fluid. Seal material selection is independent of housing material and must match the fluid chemistry precisely. Seal failure leads to fluid leakage, environmental contamination, and potential pump damage.
Viton Standard for All NAPCO Chemical Pumps
NAPCO's chemical transfer pump lineup standard specification is Viton elastomers (FKM) in both high-pressure and low-pressure seal sets. Viton provides superior chemical resistance across a broader range of fluids compared to nitrile, with excellent compatibility to aromatic solvents, chlorinated hydrocarbons, and strong oxidizers.
Viton provides: Temperature range to 400°F; excellent resistance to aromatic solvents, oxidizing agents, strong acids, and most petroleum-based fluids; outstanding tear and tensile strength under chemical attack.
Nitrile Seals: Limited Chemical Compatibility
Nitrile (NBR) elastomers are adequate for petroleum-based fluids, water-based emulsions, and mild industrial chemicals, but fail rapidly in aromatic solvent and oxidizer environments. Do not specify nitrile for chemical transfer applications unless the fluid chemistry has been verified as compatible and non-aggressive.
Gear Material Selection for Aggressive Fluids
Gears themselves (the drive and idler gears) are typically iron-based with surface hardening. In stainless pump housings, gears are composed of ductile iron or alloy steel with hardened surfaces. The enclosed environment within the stainless housing, combined with Viton seals, protects gears from direct chemical exposure, but fluid can contact gear surfaces during operation.
Nitrile-Lined Gears (Standard for Moderate Chemicals)
NAPCO standard gear construction uses nitrile-lined tooth surfaces for corrosion resistance in moderate chemical environments. Nitrile provides wear resistance and some protection against non-aggressive fluids including mild acids, alkaline solutions, and petroleum products.
Select nitrile gears for: Mild mineral acids, alkaline solutions, petroleum products, water-based fluids, non-aromatic industrial chemicals.
Viton-Lined Gears (For Strong Acids and Solvents)
For applications involving strong mineral acids, aromatic solvents, or oxidizing agents, NAPCO offers Viton-lined gears providing superior chemical resistance. Viton surfaces resist degradation from aggressive fluids, extending gear life and pump reliability in severe service.
Select Viton gears for: Strong mineral acids (HCl, H2SO4, HNO3), aromatic solvents (benzene, toluene, xylene), oxidizing agents (permanganates, chlorine), chlorinated hydrocarbons.
System Design Considerations for Chemical Transfer
Piping Material Compatibility
Stainless steel pump selection alone does not ensure system reliability if discharge piping is carbon steel or other incompatible materials. Discharge hoses and fittings must also be compatible with the pumped fluid chemistry.
For aggressive chemical service, specify: Stainless steel piping and hose assemblies; PTFE or other chemical-resistant hose liners; avoid copper or aluminum fittings unless verified compatible with specific chemical.
Secondary Containment
Chemical transfer operations require secondary containment to capture any leakage. Design the pump installation with adequate drip pan capacity or containment berm to prevent chemical spill to the environment. Viton seals minimize leakage risk, but secondary containment is essential for regulatory compliance and environmental protection.
Heating and Cooling
Chemical fluids often require temperature management. High-viscosity chemicals may need heating to reduce viscosity and pump power consumption. Some aggressive chemicals generate heat during transfer; cooling jackets or heat exchangers may be necessary to maintain optimal temperature.
Temperature guidelines: Viton seals are rated to 400°F; nitrile to 240°F. Operating temperatures above these limits require material consultation with NAPCO engineering. Pump efficiency and seal life degrade rapidly at elevated temperatures.
Filtration
Chemical fluids often contain suspended solids, corrosion byproducts, or aggregated material that damages pump gears. Install appropriate filtration upstream of the pump inlet. A 150-micron strainer is typical; more aggressive chemicals may require finer filtration (75-100 micron).
Recommended NAPCO Models for Chemical Transfer
NAPCO offers two primary models for chemical transfer applications. Both feature stainless steel construction and Viton seals as standard.
PA300S/C — High-Volume Chemical Transfer
The PA300 series delivers high flow rates ideal for large-scale chemical transfer operations, bulk plant loading, and high-throughput process automation. At 280 RPM, the PA300S (stainless with nitrile gears) or PA300C (stainless with chemically enhanced construction) delivers 158 GPM at low pressure, maintaining 140 GPM at 100 PSI system pressure.
Specifications: 158 GPM @ 10 PSI, 26.5 cc/rev displacement, 150 PSI maximum operating pressure, stainless steel housing and shaft, Viton seals standard, nitrile or Viton gear options.
Applications: Bulk acid transfer, large-scale emulsion systems, high-throughput chemical dispensing, industrial process automation.
PA200S/C — Smaller-Scale and High-Pressure Chemical Transfer
The PA200 series provides a smaller displacement option for moderate flow applications or situations where higher pressure delivery is required. At 190 RPM, the PA200S/C delivers 69 GPM at low pressure, maintaining 60 GPM at 100 PSI.
Specifications: 69 GPM @ 10 PSI, 11.5 cc/rev displacement, 150 PSI maximum operating pressure, stainless steel housing and shaft, Viton seals standard, nitrile or Viton gear options.
Applications: Laboratory-scale transfer, small batch chemical operations, high-pressure dispensing systems, precision metering applications.
Troubleshooting: When Chemical Pumps Fail Early
Seal Leakage Within Weeks of Installation
Rapid seal failure indicates fluid-elastomer incompatibility. If a pump specified with nitrile seals is exposed to aromatic solvents or strong oxidizers, nitrile will swell and lose sealing compression rapidly. Solution: Retrofit with Viton seal kits and verify fluid chemistry for future installations.
Pitting Corrosion on Stainless Housing
304 stainless pitting in the presence of chlorides indicates the fluid contains chloride salts or aggressive components. Upgrade to 316 stainless for enhanced pitting resistance. Ensure secondary containment captures any corrosion byproducts before they spread.
Rapid Gear Wear Despite Stainless Pump
Gear wear in stainless pumps suggests inadequate inlet filtration or corrosion byproducts grinding against gear surfaces. Install or upgrade inlet strainers to 100-150 micron; consider flushing the system and replacing gears with Viton-lined versions if chemical attack is suspected.
Related Technical Resources
Need Help Selecting the Right Chemical Transfer Pump?
Send NAPCO your chemical fluid composition, required flow rate, system pressure, and operating temperature. Our engineering team will recommend the optimal material, seal, and elastomer configuration for safe, reliable chemical transfer.
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