Has your Lubricating Oil got Gas?

Entrained gas can reduce your oil lubrication effectiveness by up to 80%

Entrained gas reduces the efficiency of your lube oil, which can have negative consequences on the machinery it is supposed to be lubricating. This can range from minor consequences up to devastating effects. The longer it’s left, the worse the consequences. afda6d34-533d-484e-8f2c-b17b771d7a1b

But first, here is a description of the problem – this is about fluid aeration, it happens at high temperature and compression rates, when the lubricating oil in your equipment comes into contact with gas, bubbles form in the lube oil. When oil is aerated, it won’t give a full film, leaving sensitive components unlubricated, causing extremely premature wear rates or catastrophic failure.

Before you open a bottle of Coke or beer there are no visible bubbles, this is dissolved gas. When you open the bottle you see tiny bubbles in suspension – this is entrained gas. The same as in your oil.
There are several situations when this can occur even in closed loop systems.
Return lines where oil plunges into the tank under gravity or pressure.
Hydraulic systems under suction resistance.
Sudden pressure drops.
When process gas comes into contact with your oil.
What are the effects?
Machinery operating with entrained gas in its lube oil has the same effect as oil starvation as your lube oil is just not lubricating all of the area it was designed to. When gases in oil are compressed (eg. rolling element bearings, gear teeth and hydraulics) oil temperatures rise causing other issues and concerns. If left unchecked, the result is increased wear in sensitive and expensive components.

The lubricating oil will suffer a marked degradation in quality, enabling catalysts to deplete antioxidants and other additive packages, raising varnish potential which, in turn, can decrease tolerances and cause sticking valves (the list goes on!). Entrained gas will also dilute the viscosity of the oil, falling outside of its design specification for the given application.

Entrained gas also creates cavitation. This is caused when the pressure of the dissolved gas is higher than the fluid. When this happens the bubbles can collapse, which degrades the quality of the oil. It is also often the source of increased high-frequency vibrations and noise plus it can cause direct damage to equipment.

Finally, entrained gas in lube oil can reduce thermal conductivity, increase erosion, and decrease the efficiency of pumps.
Your solution to restore your lubricating oil
Simple bubble removers can be effective on highly aerated systems and work like mini centrifuges to spin the gas and bubbles into the middle of the vortex and then remove them. However, to remove 100% of entrained gas and 90% of dissolved gas you need vacuum dehydration.

Vacuum dehydration or VDOPS is ideally a six stage process with the added benefit of removing moisture and dirt as well as the gas. The oil is passed through a vacuum chamber at an elevated temperature, above 66 degrees is ideal for most oils for moisture or gas removal to separate the oil from water vapour and process gas. The resulting lube oil is almost completely free from gas and ready for service.
The VDOPS process in detail
Bulk Particle Removal The first stage of the process, where large particles are removed by a 10µm or greater filtration element. (Element selection differs with viscosity).
Temperature and Viscosity Adjustment- The oil is heated to above 66, which lowers the viscosity for higher flow and processing rates, and allows for vacuum dehydration to occur.
Vacuum Chamber – is where the heated oil is exposed to vacuum, where gas is removed, and water evaporated.
Fine Filtration Using absolute pleated microglass filtration media, particles as small as 2 micron can be removed (dirt, scale, rust, wear metal, silica, etc).
Multi pass procedure – Used to maximise the results, five passes are often used to achieve the targets of 100 percent entrained gas removal, and 90 percent dissolved gas removal.
Additive blending. If available, this is an optional restorative process which returns the lube oil to an as-new, or higher specification, as required.

1ce39f42-f657-4f58-8249-9739b7828019The result is lube oil that is de-gassed, clean and dry and with the added benefit of a very low particle count levels. The reading shown here is a cleanliness level of lower than ISO 4406 9/8/7 (NAS 1) on our live laser particle counter indicating very very clean oil.
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If you would like further information on this article or others, please let me know or visit our website.
Chris Baker
chris@biokem.com.au
Ph 0456 396 241

Further Reading
http://www.resnapshot.com/LUB1002.htm
http://www.machinerylubrication.com/Read/373/entrained-air-oil-hydraulic
http://www.labourtaber.com/entrained%20air%20white%20paper.pdf
http://people.eng.unimelb.edu.au/imarusic/proceedings/5/Kirchner.pdf

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