Deliquescent Breathers

Bill Needelman, Donaldson Company, Inc.; David Webb, Donaldson Company, Inc.

Water covers 70 percent of the Earth's surface, with the majority located in oceans, lakes and rivers. Water is necessary for life. Before the Industrial Revolution, water was the primary production force in manufacturing, transportation and agriculture industries, from water wheels to beasts of burden.

Of course, this is no longer the case as industry currently relies on high-performance machinery. Most of these machines use oil for lubrication, heat removal and power transmission. Modern essential oil-wetted systems include hydraulics, steam and gas turbines, engines, motors, gearboxes and electrical transformers.

As essential as water is for biological life, it can be devastating for machine life. Along with particles from dirt and wear, water is one of the two most harmful contaminants. Water problems range from corrosion to oil degradation and from plugging gels to flourishing microbial colonies. Minimizing water contamination maximizes performance, fuel efficiency, productivity and machine life.

Water Problems

Below is a list of problems caused and/or aggravated by water.

Corrosion: It is a significant problem with free water in oil. It also produces abrasive oxides, such as iron rust that abrade surfaces, block clearances and break off to damage moving parts.

Loss of Film Strength: When water contaminates the film it displaces the oil. Water cannot keep the surfaces apart, resulting in high friction, adhesive wear and even seizure.

Oil Oxidation: Water accelerates oil oxidation. Negative consequences include excessive viscosity, acidity and insoluble resins.

Additive Depletion: When additives migrate into free water, the concentration of some additives falls below effective levels.

Hydrolysis: In the presence of water, ester-based additives and synthetic fluids (such as phosphate esters and polyol esters) decompose into alcohols and acids.

Reduced Fatigue Life: Dissolved water enters microcracks in rolling contacts, dissociates into hydrogen gas and weakens steel by hydrogen embrittlement.

Microbial Growth: Negative consequences include rancid foul odors, human health problems, biomass slimes, foaming and acidic oil.

Gels: Some additives interact with water to form gels. These gels foul flow passages, reduce heat rejection and plug filters.

Transformers: Even minute amounts of water contamination will reduce the life and efficiency of a transformer.

Contamination Control

For minimum protection, it is recommended to keep water below the saturation level, generally 200 to 500 ppm for many oils and 10 ppm for transformer oils. For optimum protection it is recommended to maintain water levels at or below 30 percent saturation, generally 75 to 150 ppm for most machines and 3 ppm for transformers.

Maintaining water levels at or below 30 percent saturation alleviates the problems related to water as well as provides a safety margin against accidental spikes of contamination.

Donaldson has developed a new method for preventing the ingression of humid air. It is based on thin film technology and the fact that warm air leaving a reservoir (exhalation) has lower relative humidity than cool air entering a reservoir (inhalation).

Figure 1. Inhalation


Figure 2. Exhalation

The T.R.A.P.™ (Thermally Reactive Advanced Protection) is manufactured by coating the walls of a porous network with a thin film of water-absorbing chemicals called a deliquescent salt.

The resulting high surface area of absorbent provides rapid removal of water vapor from air while maintaining size and weight. Unlike desiccant breathers, the open porous structure presents minimal air flow restriction, so fluid flow into and out of the reservoir is not impeded.

In addition, the proprietary absorbents are not sensitive to oil mists entrained in the air leaving the reservoir.

The breather unit includes a pleated 3 µm filter to protect against the ingression of hard abrasive contaminant particles that contribute to the wear of mechanical components. It is manufactured from materials that can be safely disposed of or recycled.

As illustrated in Figure 1, during "inhalation" cold humid air entering the system is drawn over the large absorbent surface area inside the breather. The high humidity drives water into the absorbent and the majority of water vapor is removed.

This dry air maintains the water concentration below 30 percent saturation. Once inside the system, the air contacts the warm fluid and metal surfaces which increases air temperature and further reduces the air's relative humidity.

During exhalation (Figure 2), warm, dry air passes over the same absorbent. The low humidity air pulls water out of the thin films of absorbent. The rehumidified air exits the unit and is emitted into the surroundings.

The difference between the desiccant breathers and deliquescent breathers is the deliquescent's ability to release moisture back in to the air at standard temperatures. For a desiccant breather to release moisture the temperature need to be in excess of 360°F. The ability of the deliquescent to release moisture at standard temperatures gives the unit the ability to last longer.

The deliquescent breather is either absorbing or releasing moisture, depending upon the humidity of the air. This difference in relative humidity - high during inhalation and low during exhalation - is the force that drives the process.

It is also aided by the temperature change to increase the difference between the low and high humidity air. The heating of the air in the headspace creates an air that is dryer than the air that went through the breather. The result is dry oil and regeneration of the absorbent during each cycle.

Water contamination causes major problems in oil-wetted machinery. Upon invading the system, its presence may be hidden from the outside eye. Preventing water ingression in an oil reservoir is the best cure for contamination.

Desiccant breathers are successful at reducing the ingression of moisture, but they are limited by their low water-holding capacity and the need for frequent replacement. The self-regenerating breather, the T.R.A.P.™, effectively maintains the water concentration well below the saturation level of the oil. It is small, lightweight, and doesn't harm the oil.


1. Armstrong, R. and Hall, C. "The Corrosion of Metals in Contact with Ester Oils Containing Water at 60 and 150?C." Electrochimica Acta. p. 40, 9, 1135-1147. 1995.

2. ASTM D6304-04a. "Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils and Additives by Coulometric Karl Fischer Titration." March 2005.

3. Atkins, P. Physical Chemistry. 6th Ed. 1998.

4. Beercheck, R.C. "How Dirt and Water Slash Bearing Life." Machine Design. p. 50, 7, 68-73. 1978.

5. Cantley, R.E. "The Effect of Water in Lubricating Oil on Bearing Fatigue Life." ASLE Transactions. p. 20, 3, 244-248. 1977.

6. Clint, J., Fletcher, P. and Todorov, I. "Evaporation Rates of Water from Water-in-Oil Microemulsions." Phys. Chem. Chem. Phys. 1. p. 5005-5009. 1999.

7. Donaldson Company, Inc. "Hydraulic Filters and Accessories." Catalog HYD-100. 2006.

8. Emsley, A.M. "The Kinetics and Mechanisms of Degradation of Cellulosic Insulation in Power Transformers." Polymer Degradation and Stability. p. 44, 343-349. 1994.

9. Ferner, M. "An Investigation Into Used Engine Oil Condition." Lubes'N'Greases. p. 11, 8, 15-19. August 2005.

10. Fox, M., Picken, J. and Pawlak, Z. "The Effect of Water on the Acid-Base Properties of New and Used IC Engine Lubricating Oils." Tribology International. p. 23, 3, 183-187. 1990.

11. Gernon, M. and Hemming, B. "Modern Tools Ancient Art - Metalworking Fluids and BioSynergy." Lubes'N'Greases. p. 11, 5, 19-24. May 2005.

12. Gresham, R. "Hydraulics: The Reservoir." Tribology and Lubrication Technology. p. 61, 8, 18-19 August 2005.

13. Hill, E.C. and Genner, C. "Avoidance of Microbial Infection and Corrosion in Slow-Speed Diesel Engines by Improved Design of the Crankcase Oil System." Tribology International. April 1981.

14. Hovis, J. "What Causes Humidty?" Scientific American. p. 294, 1, 100. January 2006.

15. Jada, A. and Chaou, A. "Surface Properties of Petroleum Oil Polar Fraction as Investigated by Zetametry and Drift Spectroscopy." J. Petroleum Science and Engineering. p. 39, 287-296. 2003.

16. Kell, G.S. "Thermodynamic and Transport Properties of Fluid Water." Water: A Comprehensive Treatise. F. Franks, ed. Plenum Press, p. 363-412. 1972.

17. Naylor, T., Brown, L. and Powell, K. "Microbiological Investigations of Turbine Oil Spoilage." Tribology International. p. 182-184. August 1982.

18. Needelman, W. and LaVallee, G. "Forms of Water in Oil and Their Control." Noria Lubrication Excellence Conference. Columbus, Ohio. May 2006.

19. Rao, C.N.R. "Theory of Hydrogen Bonding in Water." Water: A Comprehensive Treatise. F. Franks, ed. Plenum Press, p. 93-114. 1972.

20. Seoud, O.A.E. "Acidities and Basicities in Reversed Micellar Systems." Reverse Micelles. P.L. Luisi and B.E. Straub, eds. Plenum Press, p. 81-94. 1984.

21. Smiechowski, M. and Lvovich, V. "Electrochemical Monitoring of Water-Surfactant Interactions in Industrial Lubricants." J. Electroanalytical Chemistry. p. 534, 171-180. 2002.

22. Stenius, P. "Micelles and Reversed Micelles: A Historical Overview." Reverse Micelles. P.L. Luisi and B.E. Straub, eds. Plenum Press, p. 1-20. 1984.

23. Stoll, P. "Limits of the Vacuum Processing of Insulating Oils in the Electrical Industry." Vacuum. p. 13, 267-270. 1962.

24. Troyer, D. "Looking Forward to Lubricant Oxidation?" Practicing Oil Analysis magazine. March 2004.

25. Wasserbauer, R. "Biocorrosion in Transformer Oils." Tribology International. p. 22, 1, 39-42. 1989.

26. Winslow, R., Kemmerer, W., Naman, T. and Jenneman, G. "Effects of Bacterial Contamination on Steam Turbine Oil Systems." Tribology and Lubrication Technology. p. 61, 3, 26-24. March 2005.

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