The Lifeblood of Your Hydraulic Machine: Why Diagnosing Hydraulic Fluid is Non-Negotiable

Can you picture a human body that has no healthy blood in it? It would not be functionally able to live as we know. In the context of an industrial machine, the hydraulic fluid is that essential blood that allows those machines to run efficiently by lubricating, transmitting force, dissipating heat, and flushing out contaminants. However, hydraulic fluid is typically an afterthought until a catastrophic event occurs, and a simple machine will grind to an immediate and costly halt.

Now we have entered the territory of the maintenance champion, hydraulic fluid diagnostics, which is not simply changing the fluid when it looks dirty, but using the science of diagnostic tests to know what is happening to the fluid and how it relates to the current state of the machine, and anticipating what the level of fluid health may lead to in terms of machines problems in the future.

Beyond a "Fluid Change": The Significance of Proactive Diagnostics

Many service schedules are based on time or hours of service. This is a good start, but it creates a situation where we are either changing fluid prematurely (wasting resources) or more concerning, we are running the fluid to the end of its useful life, resulting in wear on the components and a potential catastrophic failure (ie. a pump fails catastrophically).
 
There’s where fluid diagnostics (or oil analysis, or fluid condition monitoring) comes in. You've shifted from "fix-it-when-it-breaks" maintenance to a proactive, predictive maintenance strategy. Oil analysis is really monitoring your equipment’s “blood” and reviewing subtle, problematic changes.
 
What Are We Trying to See? Key Diagnostic Tests

An effective hydraulic fluid diagnostic program will probably include a suite of test methodologies that provide insight to a fluid’s condition, and the health of the overall system.

1.Viscosity: The "Thickness" of a Fluid

What it indicates: Viscosity is the fluid's flow resistance. It is important to lubrication and power transfer.

Why is this important:

Too low: Indicates some degree of shearing, overheating, or possible contamination by a lighter fluid, such as diesel. This causes unacceptable wear and leakage.

Too high: Cept is indication oxidation, contamination by a heavier fluid, or insufficient cooling. This leads to sluggish operation, increased power consumption, and reduced cold start performance.

2. Acid Number (AN) or Total Acid Number (TAN): Fluid Breakdown

What it tells you: Indicates the level of acid in the oil. Acids are produced over time as the fluid oxidizes or breaks down.

Why it matters: High acid numbers indicate fluid breakdown. Acids are corrosive and can attack seals and metal parts leading to failures.

3. Particle Count: The Silent Killer

What it tells you: Measures the quantity and size of solid particles (contaminants) in the fluid, typically referred to using ISO cleanliness codes (e.g., ISO 4406: 22/18/13).

Why it matters: Solid particles are the primary cause of hydraulic component wear and failures. Parts as small as one micron can cause abrasive wear on precision components like pumps and valves.

4. Elemental Analysis (Spectroscopy): Wear Metals & Contaminants

What it tells us: Identifies and measures the quantity of various elements present in the fluid.

Why it matters:

Wear Metals: Iron (Fe), Copper (Cu), Chromium (Cr), Aluminum (Al) - Specific wear from specific components (e.g. pumps, bearings, cylinders, etc.). Increasing levels indicate the potential for a component to fail.

Contaminants: Silicon (Si) - Typically an indication of dirt/dust entries. Sodium (Na) and Potassium (K) - Indicators of coolant leakage.

Additives: Zinc (Zn), Phosphorus (P), Calcium (Ca) - Level of significant anti-wear and anti-oxidant additives. Diminishing additives representation means the protection of the fluid is coming to a depletion.

5. Water Content: The Corrosive Threat

What it tells us: Measures the quantity of water in the fluid.

Why it matters: Water is a highly corrosive environment for hydraulic systems. It can cause:

• Corrosion of metal parts.
• Degradation of additive components of fluids.
• Costly reduction for lubricity (increased wear).
• Freezing in cold weather, causing blockage.
• Cavitation.

6. Fourier Transform Infrared (FTIR) Spectroscopy: The Big Picture

What it tells you: This will give a "fingerprint" of the fluid, representing changes in the fluids' chemical composition. 

Why it matters: Will give evidence of oxidation, nitration, additive depletion, and perhaps foreign fluids added (diesel, the wrong hydraulic oil, etc.) by comparing current fluid spectra to the baseline.

The value of hydraulic fluid diagnostics: 

Go longer between changes: Only replace the fluid when necessary, saving money in fluid change and disposal. 

Minimize downtime: Detect problems sooner to plan maintenance instead of having emergency maintenance or repairs. 

Extended component reliability: Help identify and take action on potential sources of wear, protecting valuable pumps, motors, and valves. 

Maximize performance: Ensure your fluids are operating at their maximum level of efficiency to minimize sluggishness and overheating. 

Environmental benefit: Less wasted fluid also equates to less of an environmental footprint.

Hydraulic Fluid Diagnostics: Getting Started

Establish a baseline: Test new fluid to get a sense of the original characteristics.

Sample on a regular basis: Maintain consistent sampling on a regular schedule, from established points universally.

Use a recognized laboratory: Partner with a knowledgeable and focused oil analysis laboratory to receive accurate and meaningful reports.

Know the results: Don’t just look at the numbers, know what they are saying about your machine and operation.

Take steps: Take the information and better informed maintenance steps.

Conclusion
Your hydraulic system is a workhorse and the hydraulic fluid is the heart of its operation. By taking on robust hydraulic fluid diagnostics, you are not only accomplishing maintenance, you are investing into the longevity, reliability and efficiency of your valuable machinery. Stop guessing, start knowing and unleash the potential of your hydraulic assets.