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Complete Guide to Spiral Classifiers: Low Weir, High Weir & Submerged Types Compared

Core Equipment for Mineral Processing & Sand Washing: Differences, Working Principles, and Selection

2026-04-23

Complete Guide to Spiral Classifiers: Low Weir, High Weir & Submerged Types Compared

The spiral classifier is a widely used classification and sand washing device in mineral processing, sand plants, and gravity concentrators. It is often paired with a ball mill to form a closed-loop circuit for pre-classification, check-classification, desliming, dewatering, or particle size classification of slurry.

1.Working Principle

The spiral classifier is installed in an inclined semicircular trough. A longitudinal shaft with rotating blades is driven by an upper transmission mechanism, while a lower spiral lifting device is provided. The classification principle is based on the difference in settling velocity of solid particles in liquid due to variations in particle size and specific gravity. Fine particles float and overflow as slurry, while coarse particles settle at the bottom and are pushed upward by the spiral blade, completing mechanical classification.

2.Technical Specifications & Applications

Spiral Diameter: 500 – 3000 mm

Trough Length: 4500 – 14300 mm

Production Capacity (Sands Return): 8 – 3.2 t/d

Production Capacity (Overflow): 32 – 1410 t/d

Applicable Overflow Particle Size: 0.83 mm – 0.07 mm

Applications: Pre-classification and check-classification in grinding circuits of mineral processing and sand plants; desliming and dewatering in sand washing operations

Suitable Materials: Various ores

3. Detailed Comparison of Three Spiral Classifier Types

Based on the spiral position relative to the slurry surface, spiral classifiers are divided into low weir, high weir, and submerged types.

3.1 Low Weir Spiral Classifier

Structural Feature: Overflow weir is lower than the spiral shaft.

Advantages / Disadvantages: Small settling area; limited classification capacity.

Current Usage: Rarely used today. Only applied for washing low-clay ores or coarse material dewatering. Seldom used in grinding circuits.

3.2 High Weir Spiral Classifier

Structural Feature: Overflow weir is higher than the spiral shaft but lower than the upper edge of the spiral at the overflow end.

Subtypes: Single-spiral high weir, double-spiral high weir.

Advantages: Larger settling area; weir height adjustable to modify classification particle size.

Typical Application: Most commonly used in grinding circuits for general particle size classification.

Complete Guide to Spiral Classifiers: Low Weir, High Weir & Submerged Types Compared 1

3.3 Submerged Spiral Classifier

Structural Feature: 4–5 spiral blades at the overflow end are fully submerged in the slurry.

Subtypes: Single-spiral submerged, double-spiral submerged.

Advantages: Large settling area; deep classification pool; minimal slurry surface disturbance from spiral agitation; stable classification surface; high and fine overflow volume.

Typical Application: Fine grinding or secondary grinding circuits; commonly used for fine particle classification in mineral processing plants.

Complete Guide to Spiral Classifiers: Low Weir, High Weir & Submerged Types Compared 2

4. Selection Guide

Type	Settling Area	Classification Fineness	Typical Application
Low Weir	Small	Coarse	Rarely used; coarse washing/dewatering
High Weir	Medium	Medium	Grinding circuits, general classification
Submerged	Large	Fine	Fine grinding, secondary grinding, high overflow fineness

5. Conclusion

The spiral classifier is a key device in grinding and mineral processing circuits. The low weir type has been largely phased out. The high weir type is the mainstream choice due to its reasonable structure and flexible adjustment. The submerged type is suitable for fine grinding applications requiring high overflow fineness. Selecting the correct spiral classifier type can significantly improve classification efficiency, reduce energy consumption, and enhance final concentrate quality.

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