The calculation process starts with estimating theoretical material flow.

Step 1: Calculate Theoretical Capacity

Example:
Assume:
Effective width (B) = 1.0 m
Material speed (V) = 0.10 m/s
Bed depth (H) = 0.03 m
Bulk density (ρ) = 600 kg/m³

This is the theoretical material flow under the assumed conditions. For a circular vibro sifter, this formula should be considered a simplified material‑flow estimation rather than a guaranteed machine rating. Actual output depends on effective screening area, material behavior, mesh condition, and operating parameters.

Step 2: Adjust for Practical Screening Conditions

Actual capacity is usually lower than theoretical capacity because not all material will pass through the screen under real conditions. A simplified estimate is:

Example:
Assume:
Open area = 45% (0.45)
Screening efficiency = 90% (0.90)
Correction factor = 0.80

This result is a preliminary estimate. Actual production capacity should be verified according to the material, screen specification, and operating conditions.

Actual capacity is influenced by several factors.

Effective Screening Area
Screen diameter alone does not determine capacity. Only the usable screening surface contributes to separation. Areas affected by feed distribution, support structures, or blocked mesh openings may reduce actual performance.

Bulk Density
Bulk density directly affects mass throughput. The relationship is: Mass Flow = Volume Flow × Bulk Density. Materials with different densities will have different kg/h capacities even under the same screening conditions.

Mesh Size
Mesh size determines the separation point. A finer mesh generally provides smaller openings and may reduce throughput because fewer particles can pass through at the same time.

Particle‑Size Distribution
Average particle size is not enough for capacity evaluation. The percentage of undersize particles, near‑size particles, oversize particles can significantly affect screening difficulty. Near‑size particles are especially important because they require more opportunities to pass through the mesh.

Moisture Content
Moisture can reduce screening performance. Wet or sticky materials may block openings, increase particle adhesion, reduce effective open area. For difficult materials, additional screen‑cleaning measures may be required.

Yield measures how much qualified product is recovered from the feed.

Example:
Feed input: 2,000 kg
Qualified product: 1,840 kg

This means 92% of the feed becomes qualified product. However: Yield ≠ Screening Efficiency. A lower yield does not always indicate poor screening performance. If part of the incoming material does not meet the required specification, that material may correctly leave the process as reject material.

The correct capacity should be selected according to actual production requirements.

A larger machine does not always provide the best solution. The goal is to select equipment that can maintain required production rate, stable screening performance, desired product quality.

To accurately evaluate vibro sifter capacity, provide:

Dahan recommends evaluating the complete application instead of selecting equipment only according to screen diameter or nominal capacity.

Does a larger vibro sifter always have higher capacity?
No. A larger screening area can increase potential throughput, but actual capacity also depends on material properties, mesh size, moisture, particle distribution, and screening efficiency.

Can vibro sifter capacity be calculated from diameter alone?
No. Diameter only indicates part of the available screening area. Actual capacity requires evaluation of material characteristics and operating conditions.

Does finer mesh reduce vibro sifter capacity?
Usually yes. Smaller openings reduce available passage area and may increase the risk of screen blocking, especially with fine powders.

Why is actual capacity lower than theoretical capacity?
Because theoretical calculations do not include all real operating conditions, such as moisture, particle distribution, feed stability, and screen condition.

What is the most accurate way to determine capacity?
Calculation provides a preliminary estimate. Testing representative material under actual screening conditions provides a more reliable evaluation.