In part one of the Oil Analysis Series we discussed what I find to be the most effective way to break down an oil analysis report for engine oils. Specifically, key indicators that can lead us to a conclusion about what is happening with the oil without any prior knowledge about the oil, which is why I refer to it as the “Puzzle”.
Hydraulic Systems Overview
In this section, I would like to apply the same approach to hydraulic oils. First, let’s quickly discuss what hydraulic systems are.
Hydraulic systems use liquids to transmit energy, converting small forces into larger ones. The key components of a hydraulic system are:
-Pump: The pump is the heart of the system. There are three types of pumps used in hydraulic systems (gear pump, vane pump, piston pump).
-Cylinders & hydraulic motors.
-Valves: Valves are used to control the pressure, direction of flow, and volume of flow within the system.
-Hydraulic Fluid
-Reservoir
-Filter
Here is an example of a hydraulic arm on an excavator where the components are identified:
Tip: A few things to keep in mind when choosing a hydraulic oils are:
-Where is operation occurring (inside a temperature controlled environment or outdoors with fluctuating temperatures.
-Are fire resistant fluids required? If yes, an ester or glycol based product should be used. Note that ester based products are not compatible with natural rubber seals. Esters are considered safe for the environment.
-Is there an environmental/biodegradable concern in the event oil is spilled or leaks? If yes, a Zinc free oil should be used.
Hydraulic Oils Overview
Now let’s talk about what makes a hydraulic oil a hydraulic oil.
Hydraulic oils use Anti-Wear agents to prevent surface contact between two components. AW agents are a combination of zinc and phosphorus. Zinc is the carrier agent and phosphorus does all the work once it arrives on location by forming a film barrier.
These three agents will show up on a sample report within the following ranges on average:
Zinc & Phos: +/-250 to +/-300ppm
Calcium: +/- 40 to +/-70ppm
In a Zinc Free hydraulic oil, levels will look more like:
Zinc: <20ppm
Phos: +/- 300ppm
Calcium, magnesium, and barium are detergents are not usually found in hydraulic oils. These elements at high levels are indicators of motor oil. There are a few hydraulic oils on the market that contain detergents.
Any other elements should not be found in a clean hydraulic oil sample.
How to Breakdown a Sample Result
Again like Part 1, we always start by looking at the viscosity.
Note on this example that the viscosity test was run at 40ºC and the result was 49.1. Products are either run at 100ºC or 40ºC and hydraulic oils will always be run at 40ºC.
Now lets look at a viscosity chart:
If the oil on the sample was stated to be an AW 46 and the viscosity at 40ºC falls between 41.4 and 50.6, so all is well here!
What if the viscosity and the product label don’t match?
There are a few reasons why these wouldn’t match. Maybe the tech mislabeled the sample. Usually though this is because there is a contaminant present in an amount great enough to thin down or thicken up the oil. More investigating is required to figure out why these might not match up.
Contaminants
This is the perfect segway into the next step – checking what contaminants, if any, are present. If the sample kit used was a basic construction or transportation type, the contaminant section will look just like that of an engine oil sample:
Sodium or potassium presence would signify a possible coolant leak, silicon would signify dirt or possible seal particles, fuel, and soot generally would not appear in a hydraulic component.
Particle Count/ISO Cleanliness
If the hydraulic oil sample was designated for industrial/manufacturing machinery, the lab report will look a little different and include the following:
About halfway down in the chart, particle counts by micron size are categorized. I have highlighted a few sections for further explanation.
The red box indicates what size of particle is being measured – 4 microns, 6 microns, 10 microns etc. For reference, a visible human hair is roughly 50 microns and the human eye cannot see anything smaller than 40 microns.
The purple box indicates how many particles of that size were found in the sample. The orange boxes were flagged by the lab as being a bit high however this really depends on the application.
Lastly, the green box is a final ratio based on the total particle count in the sample known as the ISO Cleanliness Code. This chart better explains how the number is determined:
Put simply, the lower the numbers, the cleaner the oil. The total particle count in brand new, unused oil, can be higher than some used oil as filtration systems on machines will make the oil cleaner as the machine runs.
Wear Metals
Next, we would look at any wear metals present in the oil.
A wear metals chart by industry is very helpful to determine where the wear is occurring in the machine/what components are being affected.
Here is a great one used in trucking/construction – Wear Metals Chart
Additives
Lastly, we will focus on additives found in the oil. Just like the interpretation of engine oils, hydraulic oils will have specific additives we want to look for. If someone is using the wrong product in the wrong place, it will help us determine what the product might be.
In the case of construction equipment, many machines use engine oils in hydraulic applications. We will see this on samples in the form of high levels of Calcium, Zinc, and moderate levels of phosphorus:
If a true hydraulic oil is used, the chemistry will look more like this:
TBN & TAN
I typically do not suggest my construction or trucking customers pay much attention to the TBN (Total Base Number) or TAN (Total Acid Number) in their samples. TBN applied in times when engine oils had high sulfur levels. The only place it is applicable today is in the case of natural gas engine.
The TAN carry more weight in the manufacturing world where combustion does not occur. It is the measure of the acidity of the oil. Over time the oils cook and breakdown, forming acids. As acid forms, it is also a catalyst for more acid, so once it is present, the levels will quickly skyrocket. TAN is a great indicator that the oil is ready to change. Levels of 1.5 and higher signifies the oil is in need of replacement.
This is a very quick and simplified way to look at hydraulic oil samples. I hope it helps! Please reach out if you have any questions!