When moving from a single-head depositor to a multi-head depositor, how does the flow distribution across nozzles affect weight variation, and at what scale does this become a problem?

When scaling up production from a single-head to a multi-head depositor, the flow distribution across nozzles directly influences weight variation, and the problem becomes significant when the coefficient of variation (CV) targets fall below 2-3% for high-speed lines.

How Flow Distribution Affects Weight Variation

In a single-head system, the product is deposited through one nozzle, meaning flow consistency depends on a single path. With a multi-head system, you introduce multiple flow paths. Differences in nozzle diameter, wear, or internal obstructions cause each nozzle to deliver a slightly different volume per stroke. Even minor discrepancies-as small as 0.1 mm in nozzle bore-can lead to weight variations of 0.5-1.5% between nozzles. Over a production run, this creates a bimodal or spread-out weight distribution.

The key mechanism is binomial flow splitting: in a multi-head depositor, the total flow is divided among nozzles, and any imbalance in the split (due to manifold design, viscosity changes, or nozzle resistance) amplifies weight variation. For example, if one nozzle delivers 2% more than average, and another 2% less, the standard deviation of the final product increases significantly.

At What Scale Does This Become a Problem?

The problem emerges when you have 4 or more nozzles operating simultaneously at high speeds (above 60 deposits per minute per nozzle). At lower scales (2-3 nozzles), manual adjustment and balancing can compensate. However, at 8 to 16 nozzles, the compounding effect of small flow variances becomes statistically significant.

Specifically, the issue becomes critical when:

• Target fill weights are below 1 gram: Small absolute weight differences become large relative errors.
• Production speeds exceed 200 deposits per minute: The time for individual nozzle adjustment is reduced, and cumulative errors grow.
• Product viscosity changes during a run: Temperature-sensitive formulations (e.g., softgels, gummies, or suspensions) cause flow properties to drift, exacerbating nozzle-to-nozzle differences.

Mitigation Strategies for Manufacturers

To minimize weight variation in multi-head depositors, focus on these areas:

1. Nozzle calibration and maintenance: Regularly measure and adjust flow rates per nozzle using precision flow meters. Replace worn nozzles proactively.
2. Manifold equalization: Ensure the feed manifold distributes product evenly. Use flow restrictors or adjustable orifices to balance each leg.
3. Real-time feedback systems: Implement weigh-scale checkweighers that adjust depositor timing or pressure dynamically. This corrects for drift within a few cycles.
4. Process control for viscosity: Maintain consistent product temperature and shear history to reduce viscosity variability.

While we cannot make medical or health claims, we can assure you that proper engineering of multi-head systems-such as those designed with precision nozzles and feedback control-can keep weight variation within 1% CV even at high nozzle counts. Without these controls, problems become evident when scaling beyond 4 nozzles or when targeting fill weights under 1 gram. Always consult with your equipment supplier to validate your specific product and speed requirements.