Hydrocyclone Cut Size & Partition Curve Calculator
Build the raw and corrected hydrocyclone partition curve from measured size-fraction data, and read the d25, d50 and d75 cut sizes plus the Ep sharpness — all by log-size interpolation, with no empirical geometry model.
Size-class partition data
Enter each size class with its % reporting to underflow. Add a water split below for the corrected curve.
| Size (µm) | % to underflow | |
|---|---|---|
Cut size & sharpness
Everything runs in your browser. Inputs are never saved or transmitted.
- Enter at least two size classes with partition or mass data.
Cut sizes are interpolated in log particle size and are not extrapolated beyond the measured range.
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter each size class (µm) with the percent of that class reporting to underflow.
- Optionally enter the water split to underflow (Rw) to remove the bypass and get the corrected curve.
- Read d25, d50 (the cut size), d75, the Ecart Probable (Ep) and the d75/d25 sharpness ratio.
How it works
The partition (or Tromp) curve is the fraction of each size class that reports to the underflow. From directly paired masses it is class mass to underflow ÷ class mass in feed. Because fine particles follow the water, a fraction bypasses to underflow regardless of size; the corrected partition removes it: Pc = (P − Rw)/(1 − Rw), where Rw is the water split to underflow.
Cut sizes are read where the corrected curve crosses 25%, 50% and 75%, interpolated in log particle size (sieve openings are geometric, not linear). The Ecart Probable Ep = (d75 − d25)/2 measures separation sharpness, and d75/d25 is the sharpness ratio. Cut sizes are never extrapolated beyond the measured range — if a level is not bracketed the tool says so rather than inventing a value.
Worked example
Corrected partitions 8–94% across 45–300 µm. With corrected partitions of 8, 20, 38, 62, 82 and 94% at 45, 75, 106, 150, 212 and 300 µm, log-size interpolation gives d25 = 82.565 µm, d50 = 126.095 µm and d75 = 187.824 µm, so Ep = (187.824 − 82.565)/2 = 52.629 µm.
Common mistakes
- Reading a raw d50 as the true cut size when a large water bypass is present — apply the Rw correction first.
- Interpolating in linear size instead of log size, which shifts the cut size.
- Extrapolating d-values beyond the coarsest or finest measured class.
Frequently asked questions
Why not just predict d50 from the cyclone geometry?
Universal geometry-only equations need site calibration and create misleading precision. Measured partition data is the reliable, honest default; this tool uses it directly.
What is Ep?
The Ecart Probable, (d75 − d25)/2 — the half-width of the partition curve around the cut. A smaller Ep means a sharper, more efficient separation.
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Cite this tool
Zerdly. (2026). Hydrocyclone Cut Size & Partition Curve Calculator. Retrieved from https://www.zerdly.com/tools/hydrocyclone-cut-size-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.