Which hydraulic fluid is most commonly used?

Mineral oil is the most commonly used hydraulic fluid due to its excellent properties for hydraulic applications. It has a high lubricating capability, which helps reduce wear on system components, and it provides good thermal stability, ensuring reliable performance across a range of temperatures. Mineral oil typically has a high flash point, reducing the risk of fire, and it is cost-effective, making it widely accessible for various hydraulic systems.

Furthermore, mineral oil can be easily refined and treated to enhance its properties further, such as improving its viscosity and adding additives for better performance under varying conditions, including anti-wear and anti-oxidation properties. This versatility and reliability make it the preferred choice in the industry compared to other fluids like water, which can cause corrosion and isn't as effective as a lubricant, vegetable oils which can have limitations like biodegradability and lower thermal stability, and ATF (automatic transmission fluid), which is specifically formulated for transmissions rather than general hydraulic applications.