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Heavy machinery helps build our homes, roads, hospitals, shopping centers, and other incredibly important structures we need in our day-to-day lives. Hydraulic systems help these machines function; society couldn’t run nearly as smoothly without them. The lynchpin of these systems is the oil used within the cylinder. This oil creates fluid energy due to pressurization. The fluid energy then converts into mechanical energy to power heavy equipment. Looking at the bigger picture, we discover that learning how to choose the right hydraulic oil for your system is a critical step in preserving the lifespan of machinery and, thus, our society’s infrastructure.
Pump Design and Viscosity Requirements
After breaking down the anatomy of a lubricant, we discover that one of its most important features is its viscosity. Without the correct viscosity, the system cannot function correctly or create enough fluid power.
Selecting an oil with the correct viscosity is one of the most important factors to consider when choosing the right hydraulic oil for your system. Your pump’s original manufacturer should have instructions indicating which viscosity range best suits your pump’s design, but you can follow some general ranges.
First, let’s break down pump designs into three categories: vane, piston, and gear pumps. Piston pumps generally require a viscosity range of 10 to 160 centistokes (cST), and vane pumps function at a similar range of 14 to 160 cST. Gear pumps come in internal and external forms and offer various viscosity choices. Internal gear pumps can reach 2,200 cST, while external gear pumps cap at 300 cST. One system is not necessarily better than the other, as they all have pros and cons.
Anti-Wear and Corrosion Protection
Your machinery may encounter two main types of corrosion: chemical and rust. Rusting occurs when water contacts ferrous metal, while chemical corrosion typically comes from the acid that forms during oxidation. Rust inhibitors are a necessary additive; almost all hydraulic oils come with it, but this doesn’t protect your machine from acids. Detergent additives help neutralize the acid and zinc oil additives bond to metal parts, essentially creating a barrier that protects the metal against chemical corrosion. Ensuring the oil you choose has at least one rust inhibitor and one corrosion inhibitor is critical.
Thermal and Oxidation Stability
No matter how high-quality your hydraulic oil is, it will oxidize over time and begin to form harmful acids and sludge that will damage components. This chemical process is normal, as the interaction of O2 and oil will naturally form acids. However, repeated exposure to high-temperature operations will speed up this process. Not only that, but high temperatures will cause your oil’s viscosity to drop.
This drop in viscosity means you must look for hydraulic oil with quality oxidation additives. Additionally, compare the general heat range in which your system functions to what the oil can withstand, which should be in the product’s description.
Ultimately, some of these additives may be more or less important depending on your application and the environment in which your machinery functions. If you’re unsure which hydraulic oil to choose, it’s always a good idea to contact your OEM so they can give you specific recommendations.
