World-class condition monitoring of hydraulic systems involves the successful integration of a number of strategic elements. While in the past, walk-around inspections and gage data were the primary means of monitoring system health, today’s modem oil analysis programs apply a host of sophisticated new tools and instruments. Reliability teams at the plant site frequently commission small laboratories. In many cases the instrumentation suite includes portable and unattended sensors. The situational context is changing too as today’s hydraulic systems are increasingly designed for higher pressures, speeds, and temperatures. This paper presents a review of strategic elements that, when well conceived and implemented, can deliver vital aiding information for achieving even the toughest condition-based maintenance goals. These include the selection of test slate, deployment of incipient failure advisories, setting of targets and limits that define nonconforming conditions, exception testing, and proactive maintenance.

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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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Historically, water contaminated oil has been said to exist in two states:

• Dissolved water (bound molecularly in the matrix of the oil)
• Free water (not molecularly bound)

In the last 30 years or so, most of the literature, including Noria’s publications, refer to water as having three states. Free water has been redefined as being water that, by force of gravity, will phase out of the oil. This means it will separate below (most common) or above the oil phase depending on oil density.

The new third state is emulsified water. Water that is held tightly in micro-globules in the oil is no longer referred to as free water. Instead, it has been more accurately referred to as emulsified water, or a “micro-emulsion”.

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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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Most of us are well aware of the enormous damage water can exact on a machine and its lubricants. However, the magnitude of this potential destruction seems to depend directly on five enabling factors. These factors are listed below and are further diagramed in Figure 1.

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