What type of liquid is mainly used in hydraulic systems?

Hydraulic systems primarily utilize oil as their working fluid due to its key properties that make it suitable for the demands of hydraulic functions. Oil has a high viscosity, which helps maintain the pressure required for mechanical operation while minimizing leaks and providing efficient energy transmission through the system. Additionally, oil has excellent lubrication properties that help reduce friction between moving parts, enhancing the longevity and durability of the hydraulic components.

Hydraulic systems ideally require a fluid that can efficiently transmit force, and oil's ability to maintain a stable viscosity across a range of temperatures allows for reliable performance. Furthermore, oil is less likely to corrode the metal components within the hydraulic system compared to other liquids, ensuring the integrity of the system over time. While other options may serve lubrication or other functions, they do not meet the comprehensive requirements of hydraulic systems as effectively as oil does.