Most maintenance and reliability professionals are aware that contamination is a major problem for lubricants and machines, but often they focus on addressing particle contamination through filtration or other removal methods after the problem is already present. While filtration is certainly important, there is another destructive contaminant that can also accumulate in lubricating oils which filters cannot remove on their own: moisture.
Water is everywhere. And without the right protections in place, it is also inside your lubricants and your machines. Dehydrators or other expensive equipment might help remove water in oil, but the most efficient way to deal with moisture contamination is to stop it from ever entering your machines or lubricants in the first place. You may be aware that desiccant breathers are used for this purpose, but this article focuses on how to actual reduce costs and improve reliability through better moisture protection.
Many experts consider moisture accumulation in lubricating oils a chemical contaminant. The destructive and disruptive capacity of moisture in lubricants must not be overlooked.
As with particle control, maintenance personnel must take care to minimize entry of moisture to curtail damage within turbines, gearboxes, or hydraulic systems. Keeping moisture out is not always easy, but it can help prevent downtime, avoid added labor expenses and reduce potential costs of replacing oil or damaged parts.
To achieve these savings does not necessarily require major expenditures. One of the most cost-effective ways to prevent contaminants from entering machinery is by using desiccant breathers.
Finding the right breather for an application is a good first maintenance consideration when attempting to extend a system’s life. More and more original equipment manufacturers (OEMs) are choosing to supply desiccant breathers on their products. While this is a positive trend in the industry, not all desiccant breathers are the same. OEM recommendations, though useful, may not be the final word on the optimal breather choice for the specific application and operating environment of your machine.
That’s why it can be helpful to partner with a breather supplier who can help guide you in choosing, properly installing, and integrating desiccant breathers into your lubrication or contamination control program.
Every industry creates its own unique environment, resulting in contamination peculiar to that industry. Because each application is unique, the optimal breather is not the same in every application. Desiccant breathers are particularly useful in environments that contain high dust and humidity levels, but they can also help to exclude moisture from in-storage lubricants in more controlled conditions. Excluding contaminants before they can start doing damage costs about 10% what it does to eliminate them once they are already present in your machines and in-service lubricants.
There are a number of ways that contaminants can enter equipment, including poor oil top-up and sampling methods, improper handling practices, inadequate or poorly maintained seals and the lack of breather filters. The abrasive effects that particles have on hydraulic pumps, turbines or gearboxes are obvious. The effects water has on moving parts are less readily understood but just as important.
In this case, we’re not talking about steam, water, and ice. When water is present in oil, it can exist in three states: dissolved, emulsified and free. Individual water molecules dispersed throughout oil are considered to be dissolved. Many are not aware that even “new” lubricating oil can have dissolved water at levels between 200 ppm to 600 ppm. It’s important not to assume that new oil is necessarily “clean” oil.
In fact, the older the oil, the more water it can hold. At some point the oil becomes saturated and the individual water molecules begin to coalesce, creating microdroplets and a cloudy appearance. As the amount of emulsified water in the oil increases, a layer of free water is produced, which settles to the bottom of tanks and sumps.
Once water has mixed with oil, chemical reactions occur between the water, base oil and various additives, including extreme pressure and wear resistance agents, oxidation and rust inhibitors and viscosity improvers.
The chemical reaction is called hydrolysis. Through this process, water can accelerate the oil’s aging rate tenfold. These chemical reactions 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.
Additionally, vaporous cavitation, the implosion of water vapor within pressurized systems, can produce honeycomb pitting on mechanical surfaces.
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 can attract and retain water—and a micro-glass or other filter media, desiccant breathers are an important element in an effective preventive maintenance program.
They are designed to prevent moisture and particulate contaminants from entering fluid reservoirs as pressure changes occur through thermal expansion and contraction of the fluid, and through level changes caused by filling and emptying of reservoirs.
As the air passes through the synthetic filter, ideally it will retain all particulate matter down to the filter efficiency rating—1 to 3 microns is typical. Moisture is also absorbed as air passes through the silica gel.
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 can be increased.
This simple design allows the desiccant breather to be more efficient and reduces the amount of desiccant gel that each breather must contain. In applications where there are minimal volume changes and the environment is damp and dirty, new hardware options can help you control breathing to extend the service life of the breather.
Knowing when to change desiccant breathers is usually obvious because manufacturers have added dyes to the silica gel that changes colors as the gel becomes saturated.
Talk to your supplier about the environment and operating details of your application. When choosing the size of a desiccant breather, consider the amount of air exchanged (the required cubic feet per minute) for each application.
Airflow capacity must match or surpass the tank’s fill and drawdown rate. As the flow rates increase, so should the size of the desiccant breather. The best suppliers act as partners in contamination control with you, helping you understand the optimal sizing, adapters, and hardware options for your needs.
When it comes to choosing breather housing (steel or plastic), consider the operating environment carefully. While plastic housing can be sufficient for many industrial settings, steel housings are appropriate in hot, dirty environments.
A few suggested applications for desiccant breather filters include:
desiccant breathers are powerful preventive maintenance tools that can protect industrial and commercial equipment, yet they are only as good as the contamination control and maintenance practices used with them.
Proper sampling techniques, the use of system filters, application of the correct seals and the appropriate lubricant storage and disposal systems all come into play. Desiccant breathers cannot do the entire job alone, but they play a vital role in preventing lubricant contamination. As part of a contamination control program, breathers can maximize machine and lubricant life while minimizing capital and operating expenses, ensuring the greatest return on investment.