How do I choose between a screw valve and a pneumatic valve?

Start from three conditions: fluid viscosity, shot volume, and the accuracy/cycle-time requirement.

1) Low viscosity (<500 mPa·s), 0.005-0.05 mL per shot, repeatability within ±2% - a screw valve meters by volume, so the shot is not affected by viscosity drift. 2) Medium to high viscosity (500-200,000 mPa·s), 0.1 mL and above, cycle time first - consider a pneumatic valve with a pressure-stabilised supply system; simpler and cheaper to maintain. 3) Filled or abrasive fluids - prefer a screw valve with a wear-resistant stator or an enlarged flow path, and validate with a sample test first. If you are unsure, send us the fluid model, target volume (or bead width) and cycle time and we will name the model.