Hydraulic fluid is a functional component of the hydraulic system rather than a passive medium. Fluid properties directly influence system efficiency, controllability, component protection, and operating reliability.
This page outlines the primary functions performed by hydraulic fluid and the key properties referenced in technical documentation and system specifications.
Power transmission
Hydraulic fluid transmits energy from the pump to actuators through controlled pressure and flow. Consistent fluid behaviour is required to maintain predictable system response and motion control.
Changes in viscosity or the presence of entrained air can reduce transmission efficiency and affect control accuracy.
Lubrication and wear protection
Hydraulic fluid provides lubrication to pumps, valves, actuators, and other moving components. Adequate film strength and additive performance are required to reduce friction and limit surface wear under load.
Wear protection requirements vary depending on system design, operating pressure, and component materials.
Heat removal
Hydraulic fluid absorbs and transports heat generated by system operation, friction, and pressure losses. Effective heat removal helps maintain viscosity within the intended operating range and protects system components.
Thermal stability of the fluid influences resistance to degradation at elevated temperatures.
Contamination control
Hydraulic fluid carries solid particles, water, and air to filtration and separation points within the system. Fluid cleanliness characteristics influence filtration efficiency and component life.
Properties such as demulsibility, air release, and foaming behaviour affect how contaminants are managed during operation.
Key fluid properties referenced in specifications
Hydraulic fluid specifications commonly reference properties including viscosity, viscosity index, oxidation stability, corrosion protection, air release, foaming tendency, and water separation performance.
These properties are measured using standardised test methods and are evaluated relative to system design and operating conditions rather than in isolation.