Melt Pump Modes: For Single to Twin Screw Operation

The Quick Guide to Keeping Your Extrusion Line Flowing

Because nobody has time for pressure fluctuations and throughput headaches

For over 35 years, gear pumps with control systems have been the Extrusion industry standard  for stabilizing extrusion output. But here's what surprised me: after years running single-screw lines, I only knew one operating mode. It wasn't until I got into twin-screw extrusion that I discovered there were other options. Here's the breakdown of the main modes and what they actually do:

Constant Suction Pressure Mode (The Single-Screw Workhorse)

The pump speed adjusts to maintain steady pressure on the inlet side. The controller measures inlet pressure and regulates the extruder screw speed to maintain the setpoint

Why 95% of single-screw operations use this: Stabilizing the die discharge, lowering the extruder's head pressure boosts output per screw RPM by at least 10%, drops melt temperature (roughly 6-7°F per 1,000 psi reduction), and doubles the life of thrust bearings and screws. Translation: stable output, more output, cooler melt, longer equipment life.

The downside : You're stabilizing the extruder side, but discharge pressure can still vary.

Best for: Single-screw lines where maximizing stability and output of extruders with multiple resins and a single screw design.

This was the mode for years in my single-screw world. Simple, effective, and it just worked,

until I entered the Twin Screw Extrusion world.

I initially assumed that constant pressure mode would apply to twin screw systems but it took me some time to realize this isn't the case.

The Melt Pump mode Primer from PSI Polymer Systems Inc was instrumental in helping me understand the three modes used in twin screw melt pump operation. I've included it here for your reference.