Hydraulic oil is a high-performance fluid engineered to transmit power within hydraulic systems while simultaneously lubricating components, dissipating heat, sealing clearances, and protecting against wear and corrosion. Unlike ordinary lubricants, hydraulic oils must maintain precise viscosity, cleanliness, and chemical stability for predictable and safe system operation.
Hydraulic oil acts as the lifeblood of hydraulic machinery, directly influencing system efficiency, responsiveness, and service life.
Core Functions of Hydraulic Oils
✔ Power transmission from pumps to actuators
✔ Lubrication of pumps, valves, pistons, and bearings
✔ Heat dissipation and temperature control
✔ Contamination transport to filtration systems
✔ Sealing of internal clearances to maintain pressure
Key Performance Characteristics
Viscosity & Viscosity Index (VI)
Correct viscosity ensures efficient pump performance. High VI oils maintain stable viscosity across temperature variations, critical for outdoor and mobile equipment.
Anti-Wear (AW) Protection
Zinc-based (ZDDP) or ashless additives form protective films that reduce wear in high-pressure vane, gear, and piston pumps.
Oxidation & Thermal Stability
Resists breakdown at elevated temperatures, preventing sludge and varnish formation and extending oil life.
Foam Control & Air Release
Anti-foam additives prevent air entrainment, ensuring smooth actuator movement and avoiding cavitation.
Water Separation (Demulsibility)
Rapid water separation protects against corrosion, rust, and additive depletion.
Rust & Corrosion Protection
Protective films safeguard steel and non-ferrous components during operation and shutdown.
Low-Temperature Fluidity
Low pour point ensures easy pumpability and safe startup in cold climates.
Typical Mechanical & Chemical Properties
| Property | Typical Range |
|---|---|
| ISO Viscosity Grades | 22, 32, 46, 68, 100, 150 |
| Viscosity Index | 90 – 160+ |
| Flash Point | 180°C – 260°C |
| Pour Point | –20°C to –45°C |
| Density | 0.85 – 0.90 g/cm³ |
| Operating Temperature Range | –20°C to +120°C |
| Oxidation Life | 2,000 – 6,000+ hours |
| Air Release Time | ≤ 10 minutes |
| Water Separation | Excellent |
Hydraulic Oil Classification
ISO Classification (ISO 6743-4)
✔ HL – Rust & oxidation inhibited
✔ HM – Anti-wear (AW)
✔ HV – High VI, multi-temperature stability
DIN Classification (DIN 51524)
✔ HL – R&O hydraulic oils
✔ HLP – Anti-wear hydraulic oils
✔ HVLP – High VI hydraulic oils
Types of Hydraulic Oils
✔ Mineral Hydraulic Oils – economical, general-purpose
✔ Anti-Wear Hydraulic Oils (AW / HLP) – high-pressure systems
✔ High VI Hydraulic Oils (HV / HVLP) – wide temperature range
✔ Synthetic Hydraulic Oils – extreme conditions, long drain life
✔ Biodegradable Hydraulic Oils – environmentally sensitive areas
✔ Fire-Resistant Hydraulic Fluids – steel plants, mines, foundries
Hydraulic Oil Selection Criteria
| Factor | Importance |
|---|---|
| System Design | Pump and valve compatibility |
| Operating Pressure | AW vs EP requirements |
| Temperature Range | ISO grade and viscosity index |
| Operating Environment | Water exposure, fire risk |
| OEM Specifications | Mandatory compliance |
Industry Applications
✔ Construction & earthmoving equipment
✔ Manufacturing presses and CNC machines
✔ Agricultural machinery and irrigation systems
✔ Mining and heavy industrial equipment
✔ Automotive and material handling systems
✔ Marine and offshore hydraulic systems
Benefits of High-Quality Hydraulic Oils
✔ Improved machine efficiency and response
✔ Reduced wear, failures, and downtime
✔ Extended equipment service life
✔ Stable hydraulic performance
✔ Lower maintenance and operating costs