Hydrocyclone: learn about the most common faults

Hydrocyclones are equipment used to separate solids from liquids or liquids of different densities. This asset has a cylindrical-conical vessel with a tangential inlet flow at the top, an outlet at the bottom (the apex) through which the denser or larger material is removed, if it is solid – called the underflow. As well as an upper outlet for removing the less dense or smaller material – called overflow.  

The separation of the materials occurs due to centrifugal action, which forces the denser material towards the outer surface (exiting at the bottom), while the less dense material migrates towards the center of the vortex and flows out at the top.

separation in hydrocyclone

With regard to hydrocyclone operation, one point of attention is the inlet pressure. Although other factors such as the diameter of the cone and even the material can interfere with the cut-off point, pressure is one of the main factors. 

The cut-off point in classification refers to the definition of particle size separation, which divides the material entering in the overflow and the underflow.”

This is because it will influence the cut-off point (or d50): if it is below the appropriate value, the d50 will be higher than desired. Similarly, if the pressure is above the appropriate value, the d50 will be lower than desired.

Hydrocyclone Application

Despite the possibility of application in different industrial sectors, the hydrocyclone is commonly found in the mineral processing and pulp and paper industries.


It is installed in a closed circuit between the grinding and conditioning paths for flotation, and the feed is pumped under pressure through the tangential inlet, contributing to the turning movement.

In this way, the material that is already the right size follows the production flow and that which is too large returns to the mill. The hydrocyclone therefore closes the milling cycle. Sometimes there may even be a second cyclone to separate the fines from the material.

Eliminating excess fines avoids a series of flotation problems such as slimes coating (when fine particles adhere to the surface of larger ones), changes in the rheology of the pulp, which becomes more viscous, overflowing of the flotation tank and high reagent consumption.

Hydrocyclone faults

There are some problems that are quite common in this type of asset. These include low fluid flow, low levels in the tank, the presence of oil in the water, odors in the separator, and a lot of debris.

  • Low fluid flow: this can be related to pump problems, insufficient water in the reservoir, suction blockages, clogged filters or inadequate lubricants.
  • Low level in the tank: it is important to check that there are no obstructions in the pipes and filter, clean the sludge from the settling tank and, above all, adjust the pressure regulating valve.
  • Presence of oil in the water: this may indicate that the system is overloaded or that the settling tank is full. There may also be blockages in the water discharge.
  • The presence of odors in the separate: this can be an indication of accumulated sludge or stagnant water.
  • Too much debris: this problem is usually related to dirty filters or accumulated sludge.

These problems can be detected through inspections (visual, olfactory and auditory analysis of the assets). Inspections should be carried out periodically in order to prevent these situations from worsening into severe failures.

Learn more: Rota de Inspeção Sensitiva: tudo o que você precisa saber (dynamox.net) 

The possibility of using human senses to assess the condition of equipment, when used strategically, can make a difference in asset management. In other words, with the guidance and direction of the inspector’s knowledge, it is possible to identify a series of anomalies, or even serve as a double-check for signs of failure pointed out by software, such as Dynamox’s Visual Management Module.

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