Technical Resource
Pumping High-Viscosity Adhesives: Equipment Selection and Best Practices
Industrial adhesives present unique pumping challenges. This guide explains why gear pumps are the standard for adhesive transfer and how to select the right equipment for your application.
Challenges of Pumping High-Viscosity Adhesives
Industrial adhesives are not simple liquids. They are engineered formulations with extreme viscosity, temperature sensitivity, and chemical reactivity. Selecting the wrong pump technology leads to inconsistent flow, product degradation, line blockages, and production delays.
Extreme Viscosity
Industrial adhesives range from several thousand centistokes (cSt) to beyond 100,000 cSt. Standard centrifugal pumps cannot generate sufficient pressure to move such viscous fluids. Progressive cavity pumps may work but with efficiency losses and heat generation.
Temperature Sensitivity
Adhesive viscosity changes dramatically with temperature. A pump system must either heat the adhesive to maintain pumpability or be capable of handling viscosity swings without losing output consistency.
Tendency to Set Up
If a pump stops moving adhesive, the fluid can begin to set or cure in the pump and feed lines. A pump capable of self-priming and rapid restart is essential to prevent production interruptions.
Types of Adhesives and Their Pumping Challenges
Reactive Adhesives (Epoxy, Polyurethane)
Reactive adhesives cure through chemical reaction (two-part epoxy) or exposure to moisture (polyurethane). Once mixed or exposed to air, they begin to harden. The "pot life" or working window may be only minutes.
Pumping challenge: The pump must move the adhesive quickly from storage to application without delay. Any interruption shortens pot life and risks curing in lines.
Solution: Gear pumps are fast and self-priming, enabling rapid transfer.
Water-Based Adhesives
Water-based adhesives are used in wood products, cardboard, and textile applications. Viscosity is generally 5,000–50,000 cSt.
Pumping challenge: The moderate corrosion risk requires attention to material compatibility. Ductile iron is typically acceptable; stainless is used where longevity is critical.
Solution: NAPCO ductile iron pumps (PA300C, PA200C) are standard for water-based adhesive transfer in the wood products industry.
Epoxy Systems (Two-Part)
Structural epoxy adhesives require precise ratio mixing of resin and hardener. Too much or too little hardener changes cure time and strength. Industrial metering systems use separate pumps for each component.
Pumping challenge: Each pump must deliver consistent, repeatable flow to maintain proper ratio over extended operation.
Solution: Gear pumps deliver consistent, repeatable volumetric output.
Why Gear Pumps Excel for Adhesive Applications
Positive Displacement Handles High Viscosity
Centrifugal pumps work by accelerating fluid; their capacity drops drastically as viscosity increases. Gear pumps use mechanical displacement, so flow is near-constant regardless of viscosity or pressure.
Self-Priming from Drums and Totes
NAPCO gear pumps are self-priming and can draw directly from 55-gallon drums or totes without external assist. This is essential for adhesive operations where rapid changeover between products is common.
Simple Design Resists Plugging
The simple internal design of a gear pump (two gears, two shafts, a housing) leaves few internal passages where adhesive could accumulate and harden. Progressive cavity pumps and centrifugal pumps have more complex internal passages where adhesive can lodge and plug the pump.
Housing Material: Ductile Iron vs. Stainless Steel
Ductile Iron: The Standard for Most Adhesives
Most industrial adhesives are non-corrosive to iron. Reactive epoxy adhesives have excellent compatibility with ductile iron. Because most adhesives are not corrosive, ductile iron is the cost-effective choice and standard in the industry.
The PA300C ductile iron pump is the most popular NAPCO pump for adhesive applications. It delivers 158 GPM at 280 RPM and is used by major wood products manufacturers for continuous-duty resin and adhesive transfer. The PA300C has become the industry standard because it reliably handles the viscosity and volume of adhesive operations.
When to Use Stainless Steel
Stainless steel pumps are recommended for specialty adhesives that contain corrosive additives: solvent-based adhesives (containing thinners or solvents), UV-cure adhesives with chemical modifiers, or adhesives with aggressive pH (very acidic or basic). In these cases, the investment in stainless steel extends service life and avoids corrosion surprises.
For typical water-based applications, ductile iron is more economical and equally reliable.
Gear Material Selection for Adhesive Operations
Nitrile (NBR): Standard for Room Temperature and Moderate Heat
Nitrile elastomer gears are the standard offering for NAPCO pumps in adhesive applications. Nitrile has excellent chemical compatibility with water-based adhesives. The material remains elastic to 240°F, making it suitable for most adhesive operations.
Nitrile gears are cost-effective and provide reliable service life in standard applications.
Viton® (FKM): Aggressive Chemicals and Higher Temperatures
Viton® gears are optional on every NAPCO pump. Viton® extends the range; use it for aggressive chemicals and higher temperatures.
System Design Considerations for Adhesive Transfer
Pipe Diameter and Line Sizing
Adhesives require larger suction and discharge line diameters than water or oil to minimize pressure drop. A suction line sized for typical industrial fluids may create excessive backpressure on a gear pump when moving high-viscosity adhesive, reducing output. NAPCO can provide sizing guidance based on your flow rate and viscosity.
Suction Lift and Tank Placement
For adhesives, suction lines should be short and direct. Long suction lines or elbows create friction losses that reduce priming ability. Positioning the adhesive drum on a raised platform directly above the pump suction minimizes cavitation risk.
Strainers and Filtration
Contaminated adhesive (dust, hardened particles from previous batches) can damage the pump. Suction-side strainers (typically 100–150 micron) remove debris before it enters the pump. Discharge strainers are less common because backpressure must remain within pump limits.
NAPCO Pumps for Adhesive Applications
PA300C (Ductile Iron)
158 GPM, 100 PSI. The industry standard for high-volume adhesive transfer. Used by major wood products manufacturers.
View Specifications →PA200C (Ductile Iron)
69 GPM, 100 PSI. Compact option for smaller operations or mobile equipment.
View Specifications →Related Technical Resources
Need a Pump for Adhesive Transfer?
Tell us about your material viscosity, operating temperature, and flow requirements. NAPCO will recommend the right pump configuration with sizing assistance.