The approach of detecting and analyzing sludge and varnish problems in machinery is not the same as used oil analysis. In many instances this is because the evidence is not always in the oil. The sludge and varnish should be analyzed directly, using a completely different set of tests and evaluation parameters. Still, used oil analysis plays an important diagnostic role to help reveal candidate causes as well as to rule-out others.

The conditions that commonly lead to sludge and varnish problems vary, which complicates the process of identifying the root cause analytically. There are at least 25 unique lubricant degradation mechanisms leading to sludge or varnish formation.

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We’re told machines should not be allowed to swallow air. But what if they do?  What harm could be caused by this bubbly stuff anyway? Do we really have to make the machine burp? Will a few pats on the back do the trick?  For many of you, air contamination is no laughing matter. Why? Because air contamination is a serious condition.  There are five deadly problems associated with aerated oil. By aerated oil, I’m referring to entrained air, foam or both, which is the usual case.

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Several years ago, when my son was a Cub Scout, his den went on a night hike at our local wildlife sanctuary. He and I went together on this outing. We were led by a professional nature guide who worked full-time at the sanctuary. I wasn’t expecting much; after all, what can one see in the forest when it’s pitch dark?

It wasn’t long into the hike before I realized that I was nothing more than a babe in the woods. While I was concentrating on my footing along the trail, our guide was pointing out everything from faint insect smells to the luminescent trailers of caterpillars on tree branches. To her, the forest was an orchestra of sights, sounds and smells. Using only her senses, she named the species of countless birds, mammals and reptiles we encountered along the way. She was in her element … a true professional in tune with her environment. I was impressed.

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Anybody who has been in the lubrication field for at least a couple of years has likely been badgered by problems relating to air contamination. Indeed, aeration and foam present many serious reliability concerns which merit immediate attention by machinery maintainers. However, for most people, the causes are too complex to troubleshoot, leaving the root-cause mystery unsolved. Sometimes an oil change provides a suitable remedy, but too often it serves as only a temporary fix. In other words, there is a need to find why it happened.

Laboratory researchers have conducted numerous studies over the years relating to air contamination. From this body of work, we’ve learned many interesting new facts that help us both diagnose the problem and prescribe corrective actions. Some of these new insights into the causes and effects of air entrainment and foaming problems were discussed in the article “The Perils of Aerated Oil – Let Your Machine Burp”, published in the January 2005 issue of Practicing Oil Analysis.

In this column, I want to share more snippets of information that can be useful in the control of air contamination. I’m guessing that even seasoned oil analysis and lubrication professionals will pick up a pointer or two.

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Most of us know that healthy lubricants are generally clear and bright. However, as oils age they can lose their luster, and many become dark and opaque. These optical changes are often important symptoms of impending problems that, if occur prematurely, merit further analysis and corrective action.

However, in other cases they can be benign or simply the result of the oil’s normal aging process. So how do we know the difference, especially without having to perform complex laboratory analysis? Like much in the field of oil analysis, answering such questions depends first on better understanding the nature of the problem.

We can score an oil visually the same way gemologists grade diamonds; by color and clarity. An oil’s luster or brightness is influenced by both of these options.

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It takes only a small amount of water (less than 500 ppm) to substantially shorten the service life of rolling element bearings. There is a vast amount of research that supports this. Being a career-long crusader of clean and dry oil, I will certainly not argue the contrary. In fact, water’s destructive effects on bearings can easily reach or exceed that of particle contamination, depending on the conditions.

My theme for this column, therefore, is not about whether water imparts harm but rather how it does. Knowing how water attacks and causes damage helps in setting important dryness targets and also aids failure investigations post mortem. Further, when water contamination is unavoidable, understanding these water-induced failure modes can be valuable in the optimum selection of lubricants, bearings and seals for defensive purposes.

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The defoamant (also known as antifoam agents and foam inhibitors) is a common additive in many types of lubricating oils and hydraulic fluids. As the name implies, the purpose of the defoamant is to retard the formation of stable foam on the surface of the oil in the sump, gearbox, or reservoir.

Silicones, or compounds containing silicone, and acrylic copolymers are popularly used in mineral-based lubricant formulations. Lighter grade turbine oils and hydraulic fluids are generally formulated with acrylate anti-foam additives while heavier gear oils, paper machine oils, and crankcase lubricants may use silicone.

When stable foam is allowed to form there is considerable risk that effective lubrication will not be achieved. In many cases foam is merely a cosmetic concern. In other cases it is quite serious and can lead to premature failure of the oil and machine.

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