Plunger Platen Pumps and Screw Pump Assemblies are the two most mainstream pump types in two-component metering systems. A common selection approach is "look at viscosity", but viscosity is only one dimension and often not decisive. This article provides a decision table that turns selection from "experience" into "lookup".
1. Correcting a Common Misconception
Misconception: "Screw pumps have lower accuracy and plunger pumps have higher accuracy, so high-precision applications use plunger pumps."
Fact: The metering accuracy difference between pumps is not large (usually both in the ±1%-±2% range). The real determinants of system accuracy are pressure stability and retract consistency, and their relationship to pump type manifests mainly in "can stable pressure be maintained".
The real differences are:
Conclusion: If your application needs "stable pressure" (e.g., potting, preventing glue volume fluctuation as parts vary), plunger pumps suit better. If you need to handle high viscosity and fillers, screw pumps suit better.
2. Selection Decision Table
Answer 6 questions in order; the first match determines the solution:
3. Detailed Explanation of Branches
Branch 1: High Viscosity (> 100 Pa·s) → Screw Pump
High viscosity means the plunger must overcome enormous resistance, causing:
- Accelerated seal wear (pressure concentration at clearances).
- Motor overload and heating.
- Unstable output.
Screw pumps advance material through volumetric change between screw and stator, naturally friendly to high viscosity.
Note: Extremely high viscosity (> 500 Pa·s, e.g., thermal grease, bitumen-like) requires special high-pressure screw pumps (10-30 MPa output); ordinary models do not apply.
Branch 3: Constant Pressure Required → Plunger Pump
Plunger pumps are positive displacement; displacement is determined by speed and stroke, largely independent of outlet pressure. This means even if downstream backpressure fluctuates (part depth variations, adhesive backflow), output barely changes.
Typical applications:
- Potting (parts of varying depth, constant flow needed).
- Precision dispensing (glue volume consistency first).
- Coating (stable supply needed).
Counter-example: some applications actually want "higher pressure, more adhesive" behavior (e.g., squeeze compensation); screw pumps suit better there.
Branch 4: Small Flow (< 10 ml/min) → Plunger Pump
At small flow, screw pumps have a "minimum speed" limit (below it, the screw cannot self-prime and convey stably). Plunger pumps, by adjusting stroke and frequency, work stably at small flow.
Typical applications: MEMS packaging, optical adhesives, microelectronics packaging.
Branch 5: Sensitive/Curing-Prone Adhesives → Screw Pump
Screw pumps have weak shear (unlike gear pumps which stir vigorously), making them friendlier to:
- Moisture-sensitive types (e.g., some PU pretreatments).
- Catalyst systems (shear causes local overheating and premature cure).
- Optical adhesives (shear generates bubbles).
Selecting between Shenzhen Second Intelligent Equipment Plunger Platen Pumps and Screw Pump Assembly is fundamentally a trade-off between "pressure stability" and "high-viscosity/filler tolerance", not a simple accuracy comparison. Running through viscosity, filler, pressure need, flow, and shear sensitivity in sequence typically determines the solution in 5 minutes — more efficient than repeated quotation requests. After pump selection, closing the loop on system accuracy with pressure feedback, weighing feedback, and a pulsation damper completes the engineering approach.
https://secondintelligent.com/product/high-viscosity-liquid-precision-screw-pump-for-silicone-epoxy/
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