Decision tree for selecting pressure plate pumps and screw pumps-Shenzhen Second Intelligent Equipment

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".

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:

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).

4. Hybrid Solutions: The Right Answer for Most Two-Component Systems

In practice, the most efficient solution is often neither "all plunger" nor "all screw", but "screw for the critical component, plunger for the precision component".

Typical Option 1: A Component Plunger + B Component Screw

• A (resin): medium viscosity, high accuracy required → plunger pump.
• B (hardener): high viscosity, filled → screw pump.

Typical Option 2: Both Screw + Precision Metering Valve

• High-volume, continuous production.
• A high-precision metering valve (e.g., servo metering valve) does final dosing downstream.
• Pumps only "convey"; accuracy is delegated to the metering valve.

Typical Option 3: All Plunger + Large Buffer Tank

• Small-to-medium batch, batch-mode production.
• Plunger pumps supply into a large buffer tank (with agitation and degassing), which then feeds the dispensing head.
• Benefit: pump pulsation is smoothed by the buffer tank.

Key Point in Hybrid Solutions: Dead Volume Control

Regardless of combination, dead volume must be controlled:

Dead volume = all volume from pump outlet to dispensing head

Excessive dead volume causes:

• Large adhesive waste on changeover (especially for high-value adhesives).
• Long "purge" time after changeover to expel old adhesive.
• Unstable mixing ratio during changeover transition.

Control principles:

• Use small inner diameter + many elementsfor the mixing system (static mixing tube).
• Keep piping from pump outlet to mixer as short as possible.
• If long piping is unavoidable, consider a three-way switching valve(switching to a recovery drum) to avoid waste.