The Different Types of Hydraulic Fluid

Published: April 13, 2022 Last Updated: June 15, 2023 How To Series

yellow oil fluid pouring out Hydraulic fluid helps your hydraulic system dissipate heat and transfer power, and exhibits lubricating properties that keep hydraulic cylinders and components running smoothly. These fluids can also act as a sealant and, thanks to special additives, protect your hydraulic system from contamination and damaging corrosion and wear.

Each type of hydraulic oil or fluid on the market has different chemical properties and viscosities. Because of that, not all hydraulic fluids are compatible with every hydraulic system or application. Understanding the properties of different hydraulic fluid and oil types and how to choose a viscosity will prevent damage that could eventually lead to hydraulic cylinder failure and costly downtime.


Are Hydraulic Fluid and Hydraulic Oil the Same?

Although these terms are used interchangeably, they can actually mean different things. Most hydraulic fluids fall into one of three categories: synthetic, petroleum-based, and water-based. Synthetics do not contain any actual oil, so people refer to them as “hydraulic fluid.” Mineral-based fluids, however, do contain oil. To avoid any confusion, we’ll lump everything under the hydraulic fluid category and only use “hydraulic oil” when referencing specific oil-based fluids.

What Are the Different Types of Hydraulic Fluid?

Synthetic hydraulic fluid: Synthetics are chemically produced hydraulic fluids that contain additives to enhance the physical properties. Advantages vary by formula, but include higher operating temperature, enhanced lubricity, oxidation stability, fire resistance, and biodegradability. One downside is synthetics are more toxic than non-synthetic options and can damage certain seal materials.

Mineral-based hydraulic oil: These petroleum-based hydraulic fluids are derived from crude oil fractions and contain additives to improve viscosity, prevent rust and corrosion, and enhance heat resistance and wear resistance. Mineral-based hydraulic oils are popular because they cost less than synthetics but offer comparable performance.

Multi-grade hydraulic oil:  These high-efficiency, oil-based fluids contain additives to enhance the performance characteristics but are less expensive than synthetics. Some multi-grade hydraulic oil formulas also contain dyes that make it easier to identify fluid leaks in your hydraulic system.

Water-based hydraulic oil: These fluids are less common and come in water-glycol blends and oil-in-water or water-in-oil emulsions. The high water content makes water-based hydraulic oil fire-resistant and ideal for applications like mining.

Hydraulic Fluid Viscosity and Why It Matters

A fluid’s viscosity is defined as its resistance to flow and shear. Fluid viscosity comes in several grades and is the most important factor in your hydraulic system’s performance and efficiency. In fact, viscosity is even more important than the quality of the fluid used and should always be matched to your system’s operating temperature.

An important note is that fluid viscosity changes as temperatures fluctuate. Too much heat or cold can make the fluid too thin or thick for your hydraulic system, leading to friction, wear, and sluggish performance. Operating your equipment under those conditions affects performance and can permanently damage your cylinders and hydraulic system. In short, choose your viscosity wisely!

Hydraulic Oil Flammability and Safety

Hydraulic fluid and oil both require some general safety precautions, like preventing contact with the skin, eyes, and mouth. Most hydraulic oil formulas are also flammable once they reach a specific temperature or flashpoint, which is why it’s so important to avoid overheating your hydraulic system. Stay safe by always wearing gloves and protective eyewear during fluid changes and maintenance. Store hydraulic fluid away from ignition sources and use fire-resistant hydraulic fluid formulas in high-temperature applications or where there is a risk of combustion.

Remember, the chemical makeup and physical properties of each hydraulic fluid type vary by brand and fluid grade. Research fluid options thoroughly and read labels carefully before using a product in your hydraulic system. When in doubt, speak with a hydraulic system expert to get advice on choosing a hydraulic fluid for your mobile or industrial equipment.

The team at Hydraulic Cylinders, Inc. is here to answer your questions and help you find the right hydraulic cylinders and component parts for your system. Call us at 866-817-9253 to talk to a cylinder expert.

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