Technical Resource
Gear Pumps for Corrosive Chemical Transfer: Material Selection and System Design
Why Rotary Gear Pumps Excel in Chemical Transfer
Chemical transfer operations demand pumps that deliver consistent, predictable flow rates 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 is near-constant regardless of viscosity or pressure.
- Positive Displacement: Mechanical gear action moves a set volume of fluid forward with each revolution.
- 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 gear material selection is equally critical.
Classes of Chemical Attack
Oxidizing Agents: Chlorine, hydrogen peroxide, permanganates, and other oxidizers attack ductile iron rapidly.
Aromatic Solvents: Benzene, toluene, xylene, and other aromatic compounds swell and degrade nitrile rubber gears. These applications require Viton gears 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.
Stainless Steel Construction
NAPCO stainless pumps feature a stainless steel housing and shaft. This design eliminates the galvanic couple that would form between stainless components and ductile iron, ensuring uniform corrosion resistance.
Stainless Steel Benefits
Corrosion Resistance: Stainless steel resists organic acids, mild mineral acids, and alkaline solutions that would quickly degrade ductile iron.
Select Stainless Steel for: Typical chemical processing, organic acids, alkaline solutions, coastal installations, or any application where extended service life and corrosion resistance are priorities.
Shaft Material in Stainless Pumps
NAPCO stainless pumps specify stainless steel shafts rather than carbon steel shafts. This eliminates a potential corrosion pathway and ensures the wetted surfaces remain consistently stainless steel, preventing localized galvanic attack.
Gear Materials for Aggressive Chemical Service
All NAPCO pumps use Viton® seals. The gear material is the choice: nitrile is standard, and Viton® is optional for aggressive chemicals.
Nitrile Gears: Standard for Moderate Chemicals
Nitrile gears are standard on every NAPCO pump. 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® Gears: Optional for Aggressive Chemicals
For applications involving aromatic solvents or oxidizing agents, NAPCO offers Viton gears providing superior chemical resistance. Viton resists degradation from aggressive fluids, extending gear life and pump reliability in severe service.
Select Viton gears for: 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: Nitrile gears are rated to 240°F; Viton® extends the range. Operating temperatures above 240°F require material consultation with NAPCO engineering.
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: High-Volume Chemical Transfer
The PA300 series delivers high flow rates ideal for large-scale chemical transfer operations and bulk plant loading. At 280 RPM, the PA300S delivers 158 GPM at low pressure, maintaining 140 GPM at 100 PSI system pressure.
Specifications: 158 GPM @ 10 PSI, 100 PSI maximum tested pressure, stainless steel housing and shaft, Viton seals standard, nitrile or Viton gear options.
Applications: Large-scale emulsion systems and high-throughput chemical transfer.
PA200S: Smaller-Scale Chemical Transfer
The PA200 series provides a smaller displacement option for moderate flow applications. At 190 RPM, the PA200S delivers 69 GPM at low pressure, maintaining 60 GPM at 100 PSI.
Specifications: 69 GPM @ 10 PSI, 100 PSI maximum tested pressure, stainless steel housing and shaft, Viton seals standard, nitrile or Viton gear options.
Applications: Small batch chemical operations and moderate-flow chemical transfer.
Troubleshooting: When Chemical Pumps Fail Early
Pitting Corrosion on Stainless Housing
Pitting corrosion in the presence of chlorides indicates the fluid contains chloride salts or aggressive components. If pitting occurs, the application may require alternative materials or system redesign. 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 gears 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 right housing and gear material for safe, reliable chemical transfer.