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FSM: Liquid Desander – Hardware Terminology (B-FSM046)

Without proper definitions we end up making vague statements

I am very pedantic when it comes to terminology applied to cyclonic equipment. This is because there are too many sloppy salesman using poor vernacular and overselling the equipment, or selling the wrong equipment – the result is a bad name for cyclones. Without proper definitions we end up making vague statements that confuse everyone (like the photo above).

As previously discussed the desander is a subset of the mineral processing hydrocyclone. Technically the desander is a “flooded-core hydrocyclone”, since the encapsulation of the underflow prevents formation of an air-core.

The desander and hydrocyclone share essentially the same components. The following graphic identifies the main components and flow streams around both of these devices (photo on left courtesy of FLSmidth Krebs).

Flow Streams Terms

  • Inlet Stream (Qi): Incoming feed flow stream with liquid and solids
  • Overflow Stream (Qo): Outlet flow stream of liquids and essentially solids-free. For a desander Qo=Qi, but for a hydrocyclone Qo is a fraction of Qi (usually 60%-80)
  • Underflow Stream (Qu): Outlet flow stream of solids with some liquid. For a desander Qu is batch discharge with very minimal liquid content. For a hydrocyclone Qu is continuous at 20-40% of Qi.

Hardware Terms

  • Inlet (Di): Tangential or involute transition from pipe (linear) flow to vortex (cyclonic) flow pattern.
  • Vortex Finder (Do): Internal cylinder connected to the overflow stream and protruding into the body cylinder. Used to prevent short-circuiting (bypass) of solids directly from the inlet to the liquid outlet.
  • Cylinder (Dc): Main body of unit which defines the diameter for nomenclature. For example, a 10” desander or hydrocyclone has a (nominal) 10” body cylinder.
  • Cone (Angle °): Cone section located below body cylinder. Force flow reversal for bulk liquid an increases spin on particles as they move downward.
  • Apex (Du): Also called a spigot by some manufactures. It is the bottom orifice on the cone where separated solids report to the underflow stream hydrocyclone) or accumulation chamber (desander).
  • Splash Skirt: Only on a hydrocyclone and used to minimize side splashing of continuous underflow discharge.
  • Integral Accumulator: Only on a desander and used to contain the separated solids for batch discharge.

The next article will discuss two different vessel packing designs for desanders – single cone versus multi-cone.


  1. Svarovsky, L. 1984. Hydrocyclones. Technomic Publishing Company, Lancaster, PA..

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