What does hydraulic fluid do?

• A. Lubricates moving parts
• B. Transmits pressure
• C. Stores energy
• D. Cools the system

Answer: (B)

Hydraulic fluid's main job is to transmit pressure from the pump to the actuators. When the pump pressurizes the fluid inside a closed system, the pressure is carried through the fluid to pistons and other components, converting that pressure into force to move parts or operate controls. This is the essence of how hydraulic systems amplify force and enable precise control, thanks to Pascal's law, which states that pressure applied to a confined fluid is transmitted equally in all directions.

The fluid also provides lubrication to reduce wear between moving parts and helps carry away heat to keep components from overheating, which are important secondary benefits for reliability. Some systems use accumulators to store energy, but storing energy is a capability of the overall system, not the fundamental role of the hydraulic fluid itself.