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Are 80% of Hydraulic Failures Really Caused by Contamination?

I know I’ve written it dozens of times, and I’ve seen it written even more in countless documents and heard it mentioned in technical presentations: Roughly 80% of all hydraulic equipment failures are caused by contamination. But where did this “fact” originate, and when? Who conducted the “study,” and how were data collected?

First of all, I’m not questioning the validity of the statement. It makes sense that contamination in hydraulic systems causes most malfunctions and failures. If we consider contamination to be anything in the hydraulic fluid that shouldn’t be there, then dirt, water, rust, air, and wear debris from pumps, seals, and other moving parts are all culprits. But 80% is a lot. That’s four failures out of five. What about improper installation (including the wrong component), poor system design, excessive heat, and equipment abuse? Collectively, shouldn’t all these come to more than 20%? Nope, 80% is what we see most the time—although sometimes people offer a slightly more conservative figure, such as more than 70%.

We often read about how those working in hydraulics don’t receive adequate training. Hydraulics isn’t taught in most mainstream schools, so many mechanics and technicians are forced to learn on the job. It seems as if a lack of training would be a significant source of equipment failures. This is backed up by our “Troubleshooting Challenge” column. Most of the equipment failures author Bob Sheaf writes about are attributed to a cause other than contamination. So, shouldn’t lack of training itself exceed 20%? Not if contamination accounts for 80% of failures.

This topic warrants discussion, so after checking with some hydraulics experts I’'ve known for decades, we concluded that the 80% figure seems to have come about in the early 1980s, maybe earlier. So, for sake of discussion, let’s say it was first used in the early 1980s. A lot has happened in hydraulics since then, so even if 80% was dead-on 30 or 40 years ago, is it still a good number?

I posed this question a couple experts for their opinions. First, I approached the aforementioned Bob Sheaf, who has been a technical consultant for decades. In a nutshell, he wrote, “A gut feel is approximately 80% of failures are a result of the oil’s condition [he didn’t single out contamination]. However, the lack of training and knowledge of how hydraulics work is a MAJOR problem—not only with maintenance personnel and technicians, but many designers and engineers.”

I also asked Brendan Casey for his opinion. Brendan is also a long-time technical consultant and author of several books and newsletters on hydraulic maintenance, reliability, and troubleshooting. “If 80% of premature failures attributed to contamination was backed by empirical evidence 30 or 40 years ago, I doubt it would be today,” he commented, “UNLESS, heat (energy contamination) is included in the definition (of contamination). Then possibly, it may still hold true!”

Many people in hydraulics didn’t pay much attention to contamination before the 1980s. In fact, many older hydraulic systems back then only used screens to trap particles larger than, say, 50 µm. Therefore, most malfunctions probably were caused by contamination. Most of today’s systems use filters that perform much better than those of 30 years ago, so we should expect the frequency of contamination-related failures to be lower. Yet, we still see the 80% figure quoted regularly.

Granted, hydraulics technology has improved, and many components are more sensitive to contamination, increasing the need for finer filtration. But it’s probably safe to say that designers are more aware of the problems contamination can cause and have responded by specifying more sophisticated filters and filtration systems.

This is where we are today. We know that controlling contamination improves hydraulic system reliability and longevity while reducing total cost of ownership of equipment. Shouldn’t all the progress in filtration have reduced that percentage? I welcome your feedback.

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