What Is a RoTap Sieve Shaker?

A RoTap sieve shaker is a standardized laboratory instrument that agitates a stack of test sieves using a combination of rotary and tapping motions to perform sieve analysis for particle size distribution measurement. The name "RoTap" (a trademark of W.S. Tyler, now Haver & Boecker) has become a generic term for this class of sieve shaker, much like how "Sweco" is sometimes used generically for round vibratory separators. RoTap-style shakers are referenced as the standard method in multiple ASTM test procedures and are found in nearly every QC lab that supports vibratory screening operations.

The RoTap produces two simultaneous motions: a horizontal circular rotation (approximately 278 RPM) and a vertical tapping action (approximately 150 taps per minute). The rotation distributes material across the sieve surface, while the tapping provides the vertical energy that helps near-size particles orient and pass through the openings. This dual-action approach provides reproducible results that correlate well with production screening behavior — which is why RoTap data is the standard basis for selecting mesh sizes for vibratory separators.

RoTap Sieve Shaker Specifications

Why This Matters in Vibratory Screening

The RoTap sieve shaker is the laboratory instrument that produces the particle size data upon which all vibratory screening decisions are based.

• Screen selection — RoTap sieve analysis results tell you the exact particle size distribution of your material. This data determines which mesh size to install in your ScreenerKing SiftPro, SiftPro 48, SiftPro 60, or other vibratory separator.
• Quality control — Routine RoTap testing of incoming raw materials, in-process intermediates, and finished products ensures your vibratory screener is maintaining the required D50, D10, and D90 specifications.
• Troubleshooting — When your vibratory screener's output goes out of spec, RoTap analysis of the oversize and undersize fractions reveals whether the problem is a worn screen, incorrect mesh, feed rate imbalance, or a change in incoming material.
• Reproducibility — The standardized RoTap motion produces highly reproducible results lab-to-lab and day-to-day, making it the accepted reference method for settling disputes between suppliers and customers about particle size.

Related Glossary Terms

• Sieve Analysis — The test procedure performed using a RoTap shaker
• ASTM E11 — The standard for test sieves used in the RoTap
• D50 Particle Size — The median particle size derived from RoTap data
• D10, D90 — Distribution spread values from RoTap sieve analysis
• Mesh Size — The screen specification selected based on RoTap results
• Screening Efficiency — Production metric validated against RoTap data

RoTap Sieve Shaker FAQs

What is a RoTap sieve shaker?

A RoTap sieve shaker is a laboratory instrument that shakes a nested stack of ASTM E11 test sieves using a combined rotary and tapping action to separate a material sample into size fractions. The dual motion distributes material across the sieve surface and provides energy for near-size particles to pass through. It is the industry standard method for sieve analysis.

How does a RoTap compare to a vibratory screener?

A RoTap is a small laboratory instrument that processes 25-500 gram samples for particle size analysis. A vibratory screener is a full-scale production machine that processes hundreds or thousands of pounds per hour. The RoTap provides the particle size distribution data used to select the correct mesh size for the production screener — think of the RoTap as the diagnostic tool and the vibratory screener as the treatment.

How long should I run a RoTap sieve analysis?

Standard RoTap testing times are specified by the applicable ASTM method — typically 5 to 15 minutes depending on the material and mesh sizes. ASTM C136 for aggregates specifies sieving until less than 1% of the retained weight passes in one minute. Over-sieving can cause particle breakage that skews results, while under-sieving leaves near-size particles on the wrong sieve.