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FSM: Liquid Desander – Base Conditions & Geometry for Separation Duty (B-FSM055)

Some know hydrocyclone geometric designs – from Svarovsky (Ref 3)

To size a solid-liquid hydrocyclone (or desander) we start with baseline assumptions for both operation, then modify these conditions for geometry and process changes.

The base conditions that follow are for our particular sizing methodology applied to the geometric design that I have applied to a desander. This is not a “perfect” or “typical” or “standard” desander – but it is the desander family that I work with.

Base Conditions for Geometry Selection

  • Steady-state feed, overflow (O/F), and underflow (U/F) with constant feed pressure
  • Atmospheric discharge of O/F and U/F
  • Vertical cyclone orientation
  • Feed liquid is water @ 20°C (1.0 s.g. and 1.0 cP)
  • Feed solids are spherical particles with 2.65 s.g.
  • Feed concentration is <<1 vol.% (i.e. very dilute)
  • Pressure drop (inlet to overflow) is 10 psi (6.89 kPa)

These base conditions are the starting point for sizing. Modifications are applied as correction factors.

Calculation Steps (review article B-FSM-050 for terminology reference)

  1. Calculate required cut point (D50c)
  2. Plot graded efficiency curve (D50c and α)
  3. Calculate separation size (D98) and total solids recovery (%)
  4. Iterate as necessary

The next article discusses calculation of the required cut point (D50c).


  1. Plitt, L.R., “A mathematical model of the hydrocyclone classifier”, CIM Bulletin, December, 1976, pp. 115-123.
  2. Rawlins, C.H., and Wang, I. I., “Design and Installation of a Sand Separation and Handling System for a Gulf of Mexico Oil Production Facility,” SPE Production and Facilities, paper 72999, Vol. 16, No. 3, 2001, pp. 134-140.
  3. Svarovsky, L., “Hydrocyclones”, Technomics Publishing Co. Inc., Lancaster, PA, 1984.

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