A decanter centrifuge operates on the principle of accelerated settling. Particles will settle in a viscous media according to stoke’s low, which in simple form is written as follows:
If a sphere settles in a liquid of known density and viscosity, and the settling rate is measured, then by stokes low the density of the ball or sphere can be calculated if the diameter is known. Or. The diameter can be calculated assuming the density is known.

GN Decanter Centrifuge

Since in the real word, we don’t drill spherical balls, we use the equivalent spherical diameter of the irregularly shaped particles, which enables us to use stoke’s law. When the settling rates of irregularly shaped particles are measured in a liquid with known density and viscosity, the E.S.D can be calculated, assuming or knowing the specific gravity of the particles.
Two particles of the same ESD, but different specific gravities, will settle at different rates. The heavier particle will settle faster. Two particles of different specific gravities will settle at the same rate if their ESD difference compensates. A barite particle will settle at the same rate as a low specific gravity particle if its ESD is 1.5 times that of the barite particle.
With this in mind, it is importance to screen to 200 mesh (74 microns d50) with you shaker, or mud cleaner, prior to sending mud to a centrifuge with a weighted mud. This will minimize the solids drilled solids in the discharge which is returned to the active mud system.