Volumetric vs Gravimetric Feeding

One of the most important decisions when selecting a feeding system is whether to use volumetric or gravimetric feeding. Both approaches are widely used across industries such as plastics, chemicals, food processing, pharmaceuticals, batteries, and minerals. The right choice depends on factors such as material characteristics, required accuracy, process requirements, and production goals.

What Is Volumetric Feeding? 

Volumetric feeders control material flow based on volume over time. The feeder delivers a set volume of material by operating a feeding device, such as a screw, auger, belt, or vibratory mechanism, at a defined speed. 

Because the feeder meters material according to volume, the actual feed rate depends on the material's bulk density remaining consistent. If the bulk density changes, the mass of material delivered may also change, even though the feeder continues operating at the same speed. 

Gravimetric feeders control material flow based on actual weight over time. Rather than relying solely on volume, the system continuously measures the amount of material being delivered and automatically adjusts feeder operation to maintain the target feed rate.

Most gravimetric systems use load cells or platform scales to monitor weight changes. In a loss-in-weight feeder, for example, the system measures how rate at which the feeder's weight decreases as material is discharged and automatically corrects for variations in mass flow.

Because the feeder continuously measures actual material weight, gravimetric feeding can maintain accurate feed rates even when bulk density varies during production. 

How Bulk Density Influences Feeding Accuracy 

One of the primary differences between volumetric and gravimetric feeding is how each method handles changes in bulk density.

Many bulk materials do not maintain a constant density throughout production. Factors such as compaction, aeration, particle size distribution, moisture content, refill conditions, and material flow behavior can cause density variations. When this occurs, a volumetric feeder may deliver a different mass flow rate than intended because it continues to meter the same volume.

A gravimetric feeder continuously measures material weight and automatically adjusts feeder speed to maintain the desired feed rate. This makes gravimetric feeding particularly valuable for processes where consistent formulation and product quality are critical. 

Which Feeding Method Is Right for Your Application? 

Neither feeding method is universally better. The optimal solution depends on the specific process requirements.

Volumetric feeding may be sufficient when handling free-flowing materials with predictable properties and when moderate feed rate variations are acceptable.

Gravimetric feeding is often the preferred choice when accuracy, consistency, traceability, and process control are key requirements. It is particularly beneficial in applications involving multiple ingredients, demanding formulations, or materials that exhibit changing bulk density characteristics.

When evaluating feeder options, manufacturers should consider: