For persistant water ingression problems on larger systems Vacuum dehydration may make sense. But there are other less expensive options. A centrifuge is usually much less expensive to install and usually will take care of persistant water ingression. If operated on a continuous basis a centrifuge will remove free water and any sediment which forms in your system prolonging the system filter changeouts. Centrifuges are likely the most common ofline water removal system for large circulating oil systems because they offer fairly easy use and once set up only require an occasional (weekly) cleaning with no filter elements to replaceto maintain.
Water removal utilizing water absorbing filters is inefficient because these types of filters can only remove free water and some loosly emulsified water. On a chronic problem like you describe the effort of frequent changing of filter elements and the costs of the elements themselves make the long term use of filters a very expensive choics. There are water coalescing filter systems which work by increasing teh size of the water particles as they pass thru the elements until they are large enough to fall out of solution which offer longer filter life and less manpower to operate. Coalescers still only remove free water and do a bit beter at breaking down emulsions than do water absorbing filters but do nothing for disolved water. All that being said vacuum dehydration is the most efficient at removing water as it can remove all three types of water contamination (free water, emulsified water, and disolved water).
pitmanj asked: "...why a vacuum dehydrator is more efficient?"
Using a Vacuum dehydrator is the only way to separate free, emulsified and disolved water. Other equipments can separate free water, like centrifuges. Filters, water absorbance filters and coalescing filters can handle free and even emulsified water.But by the time you are running your system with free water you are already in big problems.
The filters will get very expensive on the long term if you have lots of water, and the problem with vacuum dehydration is that it will not remove any loose particles that may get into your oil with the water or from the lubricated parts.

I think the best alternative is to use a centrifuge, it will remove loose particles and will efficiently remove all water from the systems, even if its emulsified.

We have had some experiences with emulsified water on oil and after 2 or 3 passes at 60°C the oil was completely clear.
We have had good results separating free and part emulsified water from lube oils in various envoironments. The key to good separation efficiency is heat and results down to ~200 ppm are achievable within a few passes through a hi-speed disc centrifuge (Alfa Laval type)

Hope this helps - contact me if you would like more technical information on this process at
Vacuum deyhdration is an old principle. It helps to understand how it works: Simply put, when water is placed under a vacuum it can boil off at a much lower temperature then when it is at ambient pressures. You may remember school science experiments where water is boiled in a flask and then sealed. Once it is cool you can boil the remaining water by holding the flask in your hand. It is an extremely efficient way of moisture removal and doesn't require high maintenance cost once the system is in place. But moisture, as with all forms of ingress, shouldn't be regarded as an accepted problem. In the long term, it is usually much cheaper to find the source of the problem and stop the moisture at the point of entry. Then equipment can be hired rather then purchased to remove any remaining contamination. There is a saying in Australia which is suprisingly accepted: "The oil is in good condition considering the environment in which it operates". It's important to distinguish between what is easily achievable and what is actually appropriate for a sustainable operation.
I know I'm a bit late with the input but I noticed some answers I feel are outdated and some that have very good information and need to be collated.

Your basic question is why is a vacuum system more efficient in removal of water?
First of all we need to understand what we are trying to achieve.
It has become a widely accepted practice in industry to maintain mechanical oils below 200ppm. >200ppm is regarded as free water and this will reduce component life.
What are the options?

1) to remove free water in large quantities a centrifuge (eg Alfa Laval) is a useful tool, also a coalescing unit would achieve this as well. (Please note centrifuges and coalesces will only deal with free water. This equates to water levels >200ppm.)

2) for removing emulsified and dissolved water you can’t beat the vacuum system (Hydac, Pall ect) and this will dry the oil to < 50ppm. The problem with the vacuum units is they can’t handle high volumes of free water, they get bogd down. As long as the free water remains as droplets through the oil its OK but when it comes into the vacuum chamber in litre volumes it struggles. Ideally if you had a coalescing unit first with a vacuum dehydrator second you couldn’t beat it.

3) there are packages (CC Jensen of Denmark produce a Desorber that can handle high volumes of water and keep the lubricant below 200ppm) on the market that can remove both free water and dissolved/emulsified water and guaranteed to reduce the moisture level below 200ppm

Ultimately one of the suggestions posted is crucial and that is to eliminate the problem first, always. The reality is that you will always come up against problems you can’t fix immediately and production must always come first so my suggestion is buy a system that is portable and can handle your worst, so that the equipment is always protected and you have time to plan repairs on the cause.

I hope this helps someone.
Hi all,
So far as I understand water can remain in dissolved form upto 500ppm normally, if the quantity is increased it is emulsified, and still more addition of water crosses the saturation limit of emulsification and water separates out as free water.
Here most of you have taken 200ppm as saturation point after which water comes to free stage- i think it is wrong. Once the oil has become emulsified, it is difficult for centrifuses to bring it to normal condition.Centrifuses are capable of removing only free water and a small fraction of emulsified phase, it can never remove moisture in dissolved phase.
Sanjay Prabhu, is it advisable to heat the oil to 80 degree C? There is one Klarol Oil Cleaning System which can easily remove water by heating the oil upto only 55 degree C.
The amount of dissolved water in oil depends on viscosity and type of base oil, and additives. Some higher viscous oils (e.g., ISO 100 R&O turbine oils) were found to have saturation point from 500-750 ppm, ISO 68 from 150-250 ppm, ISO 46 from 80-120 ppm, and ISO 32 from 20-50 ppm. Additives can play a major role, too. For example, zinc-based additives tend to increase the amount of dissolved water in oil, as well as some EP additives. Whatever the level (below saturation point), dissolved water does not cause any significant problems, as free and emulsified water do. Therefore, one should be aware of the “comfort” level (ppms) of his/her oil, and not trying to beat oil to death through oil dehydrator trying to get to zero or below 5 ppm of moisture.
Three methods to seperate water out of oil

1) Vacuum Dehydration
2) Coalescers
3) Cetrifuge

Each of this has its own advantages and disadvantages. The main disadvantage of a VD is the energy consumption and throughput. The main advantage of VD is ultimate dryness level. Levels below saturation limit of the oil are possible which would be virtually unattainable using a coalescer or centrifuge. One thing to realise here is the fact that a VD's performance
(both eff. and energy consuption/unit time) is greater than other mechnical means (centrifuge and coalescers) only when the water ingression rate is low. Some companies experimented with a combination of Coalescer and VD by splitting the stream into two. I am not sure whether any work has been done to check the stability of the additive package at the temperatures and pressures encountered in a VD. I know that many studies have been done in the field of coalescing to look at the effect on additive package using a coalescer.
Dear Pritmanj

Vacuum Dehydration - low temp high vacuum would be better than other methods . basic reasons - disolved additives are not seperated as would be in case of centrifuge. Also you can use a hybrid system which removes moisture / water and gasses from the lube oil (turbine oil) and then though the princ. of surface filteration removes physical impurities - if present upto recomended level by the OEM.

you need to have a carefull installation as you would require to have an filteration process which would be online. Also you need to take professional help to get the oil tested after 3-4 passess and get the same doped with the depiliated additives - due to age of the oil, process per say should not depiliate the additive levels.

Just a question - what is the capacity and do you have foaming in the system too ?

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