Which fluid is most commonly used in hydraulic systems?

In hydraulic systems, the fluid most commonly used is hydraulic oil or hydraulic fluid. This type of fluid is specifically formulated to perform a variety of critical functions in a hydraulic system. Hydraulic fluids are designed to provide effective lubrication, prevent corrosion, and maintain system integrity under a wide range of temperatures and pressures.

Hydraulic oil is typically multi-functional, offering not only the ability to transmit power but also the properties to minimize wear and tear on system components. This is essential because hydraulic systems operate under high pressures, and the fluid must remain stable and effective in these conditions. Additionally, hydraulic fluids often contain additives that enhance their performance, such as anticorrosive agents, anti-foaming properties, and anti-wear components.

Other options do not provide the same effectiveness or necessary properties for hydraulic applications. Water, while a fluid, is not suitable for most hydraulic systems due to its poor lubrication properties and tendency to promote corrosion. Compressed air is primarily used in pneumatic systems, not hydraulic systems. Thus, hydraulic oil or hydraulic fluid stands out as the most appropriate choice for ensuring the proper function and longevity of hydraulic systems.