It takes a smart dog to find hidden treasures


This article is meant as a general backup and further explanation of the information and sizing found  in the SDM Cyclone spreadsheet found at (

 Specific cyclone operations, such as dense medium cyclones are covered in separate articles.

 Cyclone operation is based on having a feed, a mixture of solids and a liquid car­rying phase, enter the cyclone under pressure, either pumped or by gravity.  This feed enters the body at a tangent.  As the feed enters the body, a rotation of the slurry begins, causing centrifugal forces to act on the particles forcing them towards the wall.  As additional slurry enters the body of the cyclone the particles migrate downward towards the cone section.  Smaller and lighter particles migrate at a slower rate due to hindered settling and may move back towards the center.  At the center of the cyclone a counter rotating central core is established by the rotating action of the slurry.  This central core (vortex) is discharged through the vortex finder as "overflow".  The mass along the wall is discharged through the apex or spigot as "underflow". 

 Classifying cyclones separate predominately based on the differential size of the particles, with the finer sized going to overflow and the coarser particles going to underflow.  Water-only or Hydro-cyclones separate based on dif­ferential specific gravity, with the lighter particles going to overflow.  Dense (heavy) medium cyclones accentuate the gravity separation by using a separating media of known and controlled specific gravity. 

  Standard Cyclone Configuration

Dimensions Standard cyclone dimensions (classifying) are based on the following relationships: 

 Cyclone diameter                 =          D

Feed inlet area                     =          I  = w *h     0.20D

Vortex finder diameter         =          d             0.43D

Apex opening diameter      =          a             0.15D

Apex cone angle                  =          ca          20 degrees

Body length                          =          B           0.60D

Feed pressure                      =          P


The standard method of writing cyclone dimensions is as follows: 

             d - .20D - .43D - .15D - 20deg. - .60D


The basic cyclone capacity is based on the above standard dimensions.  Changing these dimensions will result in a change in capacity and cyclone performance. 


Capacity Factors

  • Feed:  Capacity change is directly proportional to the square root of the head divided by 10 when head is in meters, and divided by 32.8 when head is in feet.  P = head  (m)/10 or head (H) 32.8 or lbs/in2
  • Cyclone diameter:  Cyclones small thru 10" to 14" diameter have an increased capacity per unit volume, cyclone larger than 10" to 14" diameter have a decreased capacity per unit volume. 
  • Inlet Area:  Capacity is directly proportional to "I" in centimeters. 
  • Vortex diameter:  Capacity is directly proportional to "V" in centimeters. 
  • Apex diameter:  An extremely large apex will result in increased capacity, otherwise the apex diameter has no influence on capacity. 
  • Length of body:  A change of 1.0D in length will change capacity by 10%. 
  • Cone Angle:  Standard capacity is for 20 degrees.  A 10 degree cone will increase capacity by 10%, and a 60 degree cone will decrease capacity by 10%. 
  • Slurry viscosity:  Capacity will vary directly with viscosity. 
  • Roughness of casting:  Rough castings tend to give increased capacity. 

Capacity Example:

For a standard 14" diameter classifying cyclone, or 350 mm

        350-70 - 150 - 2.25 - 20 - 230 for h = 10 Meters 

Feed capacity = 70 * (10 * 150) 1/2 = 103 cubic meter/hour = 453 g/m at 15 psi

Changing the head to 50 feet = (50/32.8)**.5 x 453 = 560 g/m

More precise calculations for other cyclone configurations can be done using the SDM Cyclone spreadsheet found at (


Classification performance is the sharpness of separation for producing a desired mesh size product.  Classification is dependent on the specific gravity of the solids, with higher specific gravity particles producing finer size separations and also more precise separations.  Classification is also dependent upon the feed con­centration with higher solids concentrations producing coarser separations.   

  • Feed pressure: Size of classification is inversely proportional to the fourth root of the feed pressure for a certain cyclone.  The effect is probable less for rela­tively large cyclones and may be greater for relatively small cyclones. 
  • Cyclone diameter: The mesh of classification is proportional to the square root of the cyclone diameter for the same pressure and same geometric shape. 
  • Body length of Cyclone: Additional cylindrical body length will decrease the size of classification.  A decrease in mesh of classification of about 30% can be obtained by increasing the body length of a given cyclone. 
  • Cone Angle: A 20o Cone angle is standard.  Reducing the cone angle to 10o will result in a significant decrease in the size of classification and a sharper separa­tion.  Increasing the Cone angle to 60o will result in a coarse classification.  The 60o Cone angle is not suitable when the feed concentration is above 20% by volume due to poor separation efficiency. 
  • Vortex Diameter: When all other dimension remain constant a decrease in size of classification of about 30% can be obtained by decreasing the vortex diameter. 
  • Feed Inlet Diameter: When all other dimensions remain constant a decrease, size of classification can be obtained by decreasing the feed inlet diameter. 

More precise calculations for other cyclone configurations can be done using the SDM Cyclone spreadsheet found at (


Factors effecting mesh of classification. 

Feeds solids concentration: The size of classification remains constant up to about 7% solids by Volume.  Increasing the feed concentration above 7% by Vol. will result in a coarser classification.  Also the efficiency of separation decreases as the feed concentration is increased. 

 Specific Gravity of solids: The mesh of classification decreases as the Sp.Gr. of the solids increase.  When the mesh of classification is known for sand (Sp.Gr. = (2.65).  The mesh of classification for magnetite (Sp.Gr. = 5.0) can be calculated: 


Coal at 1.40 Sp.Gr. will be classified about 3.5 times coarser than sand. 

 The classification for coal is not as sharp as for sand or magnetite.  This is due to the large difference in Sp.Gr. of the coal particles.  All the sand particles will have a Sp.Gr. of 2.60 to 2.70.  Coal particles of the same size will vary in Sp.Gr. from less than 1.3 to 2.70 for sand and slate and up to 5.0 for free pyrite particles.  Therefore fine heavy particles will report to the underflow and coarse light particles will report to the overflow. 

 Viscosity of feed slurry: Feed solids concentration directly effect viscosity, par­ticularly minus 325 mesh particles.  Also temperature of slurry will effect vis­cosity and mesh of classification.  A finer classification will be obtained at 110oF than at 70oF when all other factors remain unchanged. 

 It is not possible to classify sand particles coarser than about 200 microns and coal particles (Sp.Gr. 1.40) coarser than about 300 microns with a cyclone. 

 Sand particles can be classified at about 40 microns (325 mesh) with an 8" cyclone and about 60 microns with 14" cyclone. 

 The 95% point mesh of classification for 28M x 0 Raw Coal or water only cyclone C.C. will be approximately as follows: 

 Calculations for other cyclone performance for alternative cyclone configurations can be done using the SDM Cyclone spreadsheet found at (


MIke Albrecht, P.E.

o   40+ years’ experience in the mining industry with strong mineral processing experience in Precious metals, copper, industrial minerals, coal, and phosphate

o   Operational experience in precious metals, coal, and phosphate plus in petrochemicals.

o   Extensive experience studies and feasibility in the US and international (United States, Canada, Mexico, Ecuador, Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).