Breathe easy

Desiccant breathers deliver equipment reliability

by John Malone

It comes as no surprise to industrial maintenance professionals that particulate contaminants cause lubricant and hydraulic system deterioration. What might surprise some, though, is that many experts consider moisture accumulation in lubricating oil a chemical contaminant, which can be even more destructive than particle contamination.

Maintenance personnel that minimize the entry of moisture in engines, turbines, and gearboxes can reduce or prevent the associated downtime, labor, and replacement of oil and damaged parts.

Breathers offer one of the most cost-effective ways to prevent contaminants — particle or moisture — from entering machinery. Finding the right breather for the right application is the first maintenance consideration when attempting to extend a system’s life. Of late, many OEMs have chosen to use desiccant breathers to accomplish this goal.

Understanding desiccant breathers
Even though the basic concept for desiccant breathers has been the same for more than 20 years, they have evolved into numerous products that can handle a multitude of applications.

Comprised of a hygroscopic agent — silica gel that attracts and retains up to 40 percent of its weight in water — and a synthetic filter media, desiccant breathers are an important element in any preventive maintenance program. They are designed to prevent moisture and particulate contaminates from entering fluid reservoirs as pressures occur through thermal expansion and contraction of the fluid, or during filling and emptying, as they help hold down sludge deposits and water-contaminated oil.

With the addition of carbon filters, desiccant breathers can capture oil mist and evenly disperse incoming air to ensure efficient use of the synthetic filter in combination with the silica gel. As the air passes through the synthetic filter, ideally it will retain all particulate matter down to three microns, and 70 percent or more of particulate matter down to 0.5 microns. As the air passes through the silica gel the moisture adheres to the desiccant. A second filter can give added protection, as clean, dry air continues to flow through the breather vent, and then the air passes again back through the silica gel, partially regenerating it, thus extending the life of the breather.

By capturing the oil mist, the breather drastically reduces pollution in the work environment. If the breather is designed with more vent holes to allow variable airflow patterns, the filtration media and the desiccant’s drying properties will be substantially increased. This simple design allows the desiccant breather to be more efficient and reduces the amount of desiccant gel that each breather must contain. Of particular use in applications where there are minimal volume changes and the environment is both damp and dirty, the newer expansion-type breathers can control the breathing and permit expansion and contraction of the airspace. It is simple to know when to change desiccant breathers because manufacturers have added dyes to the silica gel that changes color as the gel becomes saturated.

Expand lubricant life by removing moisture
Every manufacturing industry creates its own internal environment, resulting in contamination peculiar to that industry, which, in turn, requires specific breathers. Desiccant breathers, either by themselves or in combination with other types of breathers, are particularly useful in environments that contain high humidity levels, as well as dust.

There are a number of ways that contaminants can enter equipment, including oil sampling, improper handling practices, inadequate seals, and poor maintenance, or the lack of filler breathers. The abrasive, pitting effects that particles have on engines, turbines, or gearboxes is obvious, but less understood are the effects water has on moving parts.

Despite all the attention and the millions of dollars spent to improve particle-contamination filtration technology that has reduced failure rates by as much as 90 percent, water can be a far greater danger.

Water exists in oil in three stages. Water molecules dispersed throughout oil are in a dissolved state, which can be as much as 200 ppm to 600 ppm. And the older the oil, the more water it can hold. Then, when the water exceeds the maximum level that can remain dissolved in oil, oil becomes saturated, and the water exists as suspended emulsion droplets, resembling fog. As the amount of emulsified water and oil increases, a layer of free water is produced, which settles at the bottom of tanks and sumps.

Once water has mixed with oil, a host of chemical reactions, or hydrolysis, begins to take place as it attacks oxidation and rust inhibitors, viscosity improvers and the oil’s base stock. Water can accelerate the oil’s age rate tenfold. These attacks result in varnish, sludge, organic and inorganic acids, surface deposits, and polymerization (a thickening of the lubricant). As little as one percent contamination can reduce bearing life by as much as 90 percent. The implosion of water vapor can produce honeycomb pitting on bearing surfaces.

Selection considerations
When choosing the size of a desiccant breather, consideration should be given to the amount of air exchanged (the required cubic feet per minute) for each application. Airflow and the flow of liquid must match, or surpass the tank’s fill and drawdown rate. As the flow rates increase, so should the size of the desiccant breather. It might be a wise move to consult with the breather manufacturer when trying to determine the correct size for your application. Also, there is a need to consider the operating environment when choosing which breather housing (steel or plastic) to use. While the plastic housing can be sufficient for many industrial settings, steel housings are particularly applicable in hot, dirty environments.

Applications for desiccant breather filters include:
  ► stationary and mobile hydraulic systems
  ► switch gears
  ► gearboxes
  ► turbines
  ► feed pumps
  ► agriculture equipment
  ► oil cooled transformers
  ► diesel fuel storage tanks

Closing thoughts
Desiccant breathers are a powerful preventive maintenance tool that can help protect industrial and commercial equipment from moisture and particle contaminants. It is important to note that these products are only as good as the contamination control and maintenance practices used with them. Along with desiccant breathers, proper sampling techniques, the use of the correct seals and the appropriate lubricant storage and dispensing systems all play a role in preventing lubricant contamination. Through the use of desiccant breathers and other contamination control practices, companies can maximize machine and lubricant life, while minimizing capital and operating expenses. The end result is greater return on investment.

John Malone is the Reliability Solutions Manager for Chevron Products Company. If you have lubrication questions,
contact Coach Malone at: Phone: 713-432-2647;
E-mail: jmva@chevron.com.

This article appeared in the June/July 2006 issue of MRO Today magazine. Copyright 2006.

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