Filtration, Vacuum Dehydration and Centrifuges Explained

Reconditioning lube oil requires several stages. Here is a brief tour of some of the processes involved in obtaining outstandingly clean oil.

Barrier Filters

What it does:
Barrier filters are a basic method of removing ingress. Both hard and soft particles are withdrawn from flow by filters which in the modern day are made mostly of either synthetics or microglass.

How it does it:
Filters come in different grades that are categorised by the size of holes in the mesh, and specified as either nominal or absolute (Beta rated) filters. ¬†Nominal rated filters are cheaper but not rated as well as the uniform grid mesh of an ‘absolute’ filter that can remove all particles over a given size measured in microns. ¬†Through multiple passes of lube oil through filters with smaller and smaller mesh sizes lube oil can be cleaned to a required ISO 4406 specification. Because of the passive nature of barrier filters they are easy to use and if built into a flow circuit correctly, can be easy to maintain.Vacuum1

Vacuum Dehydrators

What it does:
Water can exist in three states in lubricant oil free, suspended and dissolved. There are many relatively simple methods of removing the two former but because dissolved moisture is at a molecular scale it is harder to separate. In a previous article, Moisture Could Be Your No. 1 Lube Oil Problem, we discussed the criticality of having moisture-free oil. Corrosion, stress cracking and sludge are just a few of the adverse effects of having water in a lube system. Other methods of water removal such as using absorbent filter media are both impractical and uneconomical. Vacuum dehydration is the most efficient method of removing water in all three states.

How it does it:
Vacuum dehydration uses the relationship between temperature, pressure and phase changes to remove moisture. Before reaching the vacuum chamber the oil is heated to a carefully calibrated temperature. Upon reaching the vacuum chamber the fluid experiences a pressure that is much lower than atmospheric which, when combined with the temperature of the fluid, causes water to undergo a phase change into vapour, essentially boiling off. Separation is achieved as the water is extracted by distillation.

Centrifuges

What it does:
Centrifuges are very effective at separating contaminants from the lube oil. Bulk water removal also can be achieved with a centrifuge. The physical principle a centrifugal separator works on is the difference in densities of contaminants and lube oil; the greater the disparity in specific gravities, the more effective the process. Therefore centrifuges often work better on low specific gravity oils with low viscosities.

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A centrifuge on one of BioKem’s portable filtration systems

How it does it:
Centrifugal separation in lube oil cleaning operates in a similar manner to centrifuges in many other branches of science such as in the medical or biochemical profession. Cleverly designed mechanisms for inflow and drainage allow processing of high volumes of oil. Inside the chamber the lube flows under pressure through the internal risers of a spindle. The opposing nozzles of the spindle fire out the pressurised stream and this creates rotation (rotation can also be generated by an external motor which allows more accurate control). The rigorous spinning can mean that the oil experiences forces in the order of several thousand times that of gravity in the chamber. Naturally, more dense components in the fluid have a longer trajectory and can be captured on the wall of the rotor whereas the now clean lube oil flows down the bottom of the vessel.

Adding It All Up

A combination of barrier filters, vacuum dehydration chambers and centrifuges will make your oil cleaner by:

  • Removing hard and soft particulate ingress
  • Drastically reducing the amount of moisture present
  • Eliminating submicron contaminants

If you’re ready to have your oil be cleaned to better-than-new standards then contact us.

James McAllister
BioKem Oil Services
james@biokem.com.au

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