Micro-dosing involves placing extremely small and consistent amounts of fluid, often in the nanolitre or low microlitre range. It is common in electronics assembly, medical device manufacturing, optics and life sciences, where a fraction of a droplet too much or too little can affect product performance. Many types of liquid dispensing equipment can handle general tasks, but not every valve can deliver the control needed at such small volumes. Assessing a few specific characteristics can help you judge whether a valve is suited to micro-dosing before committing to it on a production line.
Minimum Shot Size and Resolution
The first question is whether the valve can reliably produce the volume you need. When reviewing specifications and test results, look closely at details such as these:
- The smallest shot size the valve can produce consistently, not just once.
- How finely the shot size can be adjusted between settings.
- Whether stated minimum volumes were measured with fluids similar to yours.
- The relationship between dot size and the nozzle or tip used.
- Whether the valve can switch between dot sizes without a hardware change.
Valve Design and Actuation Method
Different valve designs suit different volume ranges and fluids. Among dispensing valves commonly considered for small doses, the main options tend to work in the following ways:
- Needle valves, which control flow by lifting a needle from a seat and suit low- to medium-viscosity fluids.
- Diaphragm valves, which isolate the fluid from moving parts and suit reactive or sensitive materials.
- Jetting valves, which fire droplets without the nozzle touching the part.
- Piezoelectric valves, which allow very fast and fine control of droplet size.
- Positive displacement valves, which push a fixed volume and can reduce the effect of viscosity changes.
Repeatability at Low Volumes
Small variations matter more as shot sizes shrink. To check whether a valve can maintain consistency, it helps to evaluate points like these:
- Shot-to-shot variation measured by weight or vision inspection.
- Consistency over long runs and after pauses in production.
- Sensitivity to changes in supply pressure or fluid temperature.
- Performance on the first few shots after start-up.
Integration With the Wider System
A valve rarely works on its own. Its performance depends on how it fits into larger fluid dispensing systems, so it is worth reviewing points like these:
- Stability of the fluid supply from reservoirs, cartridges or pressure tanks.
- Compatibility with controllers, robots and motion platforms.
- Cycle speed and how quickly the valve opens and closes.
- Options for vision systems or sensors to verify each dot.
Compatibility With the Fluid
Fluid properties strongly affect how well a valve performs at small volumes. Before selecting a valve, consider factors such as these:
- Viscosity range, from water-thin fluids to thicker adhesives or pastes.
- Fillers or particles that could clog small nozzles or wear internal parts.
- Chemical compatibility between the fluid and wetted materials, such as seals and valve bodies.
- Curing or drying behaviour that could cause build-up at the tip.
- Tendency to trap air bubbles, which can cause missed or undersized dots.
Maintenance and Cleaning Requirements
Micro-dosing valves often have small internal passages that need careful upkeep. Practical considerations include the following:
- How easily the valve can be disassembled and cleaned.
- The availability and cost of replacement nozzles, seals and needles.
- How often calibration is needed after maintenance.
- Whether purge or cleaning routines can run automatically between batches.
Confirming Suitability Through Trials
Specifications provide a useful starting point, but the most dependable way to judge a valve is to test it with your own fluid, substrate and production conditions. Running trials over an extended period, and measuring results carefully, can confirm whether a valve will meet the accuracy and consistency your micro-dosing application requires.
Working with nanolitre or microlitre doses? Message Unicontrols to find a valve that fits your application.