A Comparison of Water Removal Technologies
Steffen D. Nyman
8 min
1 April 2026
Water removal from industrial oils requires matching the technology to the form and concentration of water present. This article compares vacuum, desorption, coalescing filtration, and absorption media - explaining the mechanisms, strengths, and limitations of each.
Matching Technology to Water States
The most important principle in water removal is that different technologies are effective against different forms or states of water contamination. Applying the wrong technology - or expecting a single technology to handle all forms - is a common cause of persistent water contamination problems.
Recall the three states of water in oil: dissolved, emulsified, and free. Each requires a different removal approach, and the severity of contamination determines whether a single technology is sufficient or whether a combined approach is needed.
Vacuum Dehydration
Vacuum dehydration works by heating the oil slightly and passing it through a vacuum chamber. Under reduced pressure, the boiling point of water is dramatically lowered, causing dissolved and emulsified water to vaporise and be drawn off by a vacuum pump. The dry oil is then returned to the system.
Vacuum dehydration is highly effective for dissolved and lightly emulsified water, and it can achieve very low residual water levels.
It is particularly well-suited for applications where the oil must be maintained at very low water content to prevent degradation and acidity formation. Vacuum technology does not cope well with water content higher than appr. 0.1 percent and free water, as the evaporation inside the vacuum chamber happens very violently causing the unit to trip.
Desorber Dehydration
This technology is used in CJC Desorber units and works by means of dry air. The oil is pumped into a chamber where it meets with a counter flow of dry air. The air absorbs the humidity from the oil and carries it out of the chamber.
It follows the physics of the Mollier diagram, so the colder the air and the warmer the oil is, the more water can be separated. The Desorber technology will reduce water content in most lubricants to below a few hundred ppm (below 0.03%) including specialized fluids like bio-oils (EAL), esters and glycols. Since the technology doesn’t include vacuum, it is not affected by the water states - dissolved, emulsified or free - the Desorber separates water continuously and reduces the water content in the lubricant.
A key advantage of Desorber dehydration is that it removes water without consuming any filter media - the water is simply discharged. This makes it a cost-effective long-term solution for systems with continuous water ingress and lubricants with poor water separation ability (poor demulsibility).
Coalescing Filtration (PTU Filter Separator)
The CJC PTU (Filter Separator) uses a two-stage coalescing process. In the first stage, oil passes through an acrylic-coated Linters cellulose insert where dispersed water molecules are attracted to the media and merge into progressively larger droplets. In the second stage, the oil enters a separation chamber where the enlarged water droplets are heavy enough to fall by gravity to a drain point.
The PTU can drain free water several hundred times per day and is capable of handling up to 500 litres of separated water per day in extreme ingress scenarios. Coalescing filtration is most effective for free water that separates readily from e.g. diesel, most hydraulic and turbine oils. It is less effective for emulsified and dissolved water.
Adsorptive Media (Cellulose Depth Filters or Polymers)
Standard cellulose depth filter media absorbs water in all oil states including dissolved water as oil passes through the media. This is a passive process that occurs simultaneously with particle removal.
A standard CJC insert typically absorbs up to 2 litres of water before requiring replacement; in systems with extreme water ingress, specially configured inserts can absorb up to 8 litres. Some filter inserts are using beads of Molecular Sieve or polymers instead of cellulose.
Comparison of Water Removal Technologies
Technology | Dissolved Water | Emulsified Water | Free Water | Best For |
|---|---|---|---|---|
Vacuum dehydration | Excellent | Good | Limited | Transformer oil, compressor oil, low water content targets |
Desorber dehydration | Excellent | Excellent | Excellent | Specialized lubricants incl. bio-oils (EAL), ester and glycol-based fluids |
Separation by coalescing | Poor | Poor | Excellent | Turbine oil, diesel fuel, high water ingress. Combining particle, water and varnish removal |
Cellulose depth filter | Excellent | Excellent | Excellent | Moderate amount of water ingress, combining particle, water and varnish removal |
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