Pop quiz question: What is the life of hydraulic oil?

Ask an experienced engineer and the technical answer is something like: “Depends” because the environmental variables around the fluid will have an impact on its life usefulness.

Of course, they then introduce terms like ‘Fluid Degradation, by mechanical and thermal stress’; at this point, I think of the former politician Pauline Hanson’s famous statement “Please Explain”. Yes, I am gulity of looking for simple explanations, not too simple and not too complicated, so I thought I would try and articulate ‘What is Fluid Degradation?’ in my words.

The following article has been prepared to understand what is Fluid Degradation really about?

Fluid Power Technicians/Engineers know the fundamentals’ of fluids; we know and talk a lot about Fluids in generic terms. For example, in a hydraulic application, we consider the ambient temperature of where a machine is going to operate and choose an appropriate viscosity class of oil for that environment. Then typically design a circuit around the core parameters of these limits.

Ultimately, fluid is the life blood of a fluid power system, and a good fluid power system is designed to meet an operating efficiency target. As a result, detail engineered thinking goes into selecting components and a circuit design to achieve this goal.

Over the past few months my interest in understanding “Fluids” at a deeper level has taken on a new appreciation with how the life of the fluid impacts the overall function of the machine.

Fluid quality and condition has been traced to be the leading cause of 70% equipment failures.

In a previous article;”Fluid Power – Failures are traced back to Fluid Quality“, discusses the “why is this so?” and goes on to touch on two important Fluid measurement criteria’s: 1. Fluid Cleanliness Levels and 2 Fluid Quality Condition.

From a circuit design point of view, we know filtration is an important requirement that needs to be incorporated correctly to ensure the fluid cleanliness level is maintain to prevent premature wear and to give its owners a positive Return on Investment (ROI). This filtration function is about protecting the components and removing solid contaminates floating around in the fluid. The subject of how and why there are contaminants in the fluid is for another day’s discussion.

In this week’s article, the focus is looking at the penalty of Fluid Degradation, other words, what is the fluid quality condition of the fluid. In many applications and in many workshops around the country the answer is never really understood or questioned. As a preventive management program/schedule nominates a timeframe to change the oil over.

Here is the challenge; Why? If fluid is designed to last say 15 years, yet we change the fluid every 12 months, because that’s what the Preventative Maintenance (PM) schedule said, there is an assumption made by the PM Schedule that the oil has degraded to point that it needs to be changed.. (this discussion is around hydraulic and lubrication fluids). Are we getting the most from this investment in the fluid?

In my research of this phenomenon of  “Why” , I am intrigued to learn that many organisations operate under a culture that says…. “this is how it has always been done” so we are going to stick with this same methodology?

Without getting into the change management psychology debate on this statement, this commentary is about looking at what really is a fluid and if it is designed to last 15 years then why are PM schedules demanding that it needs to be changed before time?

How do we know if the fluid is still okay and how much life is left in the Oil?

Like all parts of the fluid power system design, there is a proven science around how to size and calculate the speed and power requirements of the circuit to perform the function in the most efficient way possible. The same goes with understanding fluid, there are a number of good tests and analytical procedures that are used to test the life and condition of the actual fluid.

This interest in the ‘Fluid’ opens a new learning and respect with the science of fluid chemistry with the way fluid is designed and manufactured. Understanding chemical structure of fluid provides an insight into how and why oil degrades.

Manufacturers of the Oils design their fluids for specific applications by taking a base oil and adding a blend of important Oil additives to give it the specifications to perform its’ function. For example in a Hydraulic oil requirement there are typically four key level types of additives; these are for:

1. Controlling Chemical Breakdowns – reduce anti-aging effects
2. For Viscosity levels across temperature ranges
3. Lubricity
4. Contaminant Control

Welcome to the world of Chemical Engineering, the science of introducing oil additives is complex and intriguing. A key thought in an Oil manufactures mind, is to design a fluid that is not going to degrade? Other words, provide a genuine lifecycle ROI.AtomTesttube image

So if oil manufacturers are designing fluids not to degrade, yet we still have the effects of oil degradation, “so What is Fluid Degradation?” Reviewing many articles that also try to explain this question can leave you feeling frustrated because they often use a very simplistic approach.

At this point, I have to smile to think that the real answer I am looking for is embedded into the origins of chemistry. Now, if only, my High School Science teacher could see that finally I have an interest in this incredible topic of science and chemistry. It’s one of those life’s ironic moments for the topic of chemistry to have a strong connection to your profession.

To understand this better, I had to revisit what is chemistry? and liked the Wikipedia description. “Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry deals with such topics as the properties of individual atoms, how atoms form chemical bonds to create chemical compounds, the interactions of substances through intermolecular forces that give matter its general properties, and the interactions between substances through chemical reactions to form different substances”.

Now we are getting somewhere, the molecular structure of fluid becomes a fascinating principal to appreciate. A common term used when Oil Degradation is being explained is that it begins when a chemical reaction occurs in the fluid. For example; thermal stress (heat) on the fluid will change the molecule structure of the fluid.

In the science world, like physics there are many important natural Laws that determine how something like an atom is going to behave. In a situation, like adding thermal stress to a fluid will create a chemical reaction “The law of Conservation of Mass” becomes an important point to remember. (if you remember ….”matter can neither be created nor destroyed” ) this means that the chemical structure will change. This is where those important additives that were added to the base oil start to break apart causing the very protective elements of the fluid to stop working. Now as we get into this chemical detail, a whole new level of discussion will be required to explore the effects of what is actually happening at this chemical structure, stay tuned for part 2.


To summarise the key points, Hydraulic and Lubrications Fluid have been engineered for specific purposes and to last for a long time. Fluid is a very delicate resource, If looked after and respected it will provide a positive ROI, contrary, if not looked after, the fluid will cost an organisations many thousands of dollars of unnecessary repair. Before you change your fluid, consider the question; what is the quality of this fluid?