hydraulic oils

Hydraulic oils are the lifeblood of hydraulic systems — think excavators, presses, injection molding machines, aircraft systems — anything that relies on fluid power.
Here’s the no-fluff breakdown:

1. Core Function
    •    Power transmission: Converts pump mechanical energy into hydraulic energy to drive actuators.
    •    Lubrication: Prevents wear on pumps, valves, and cylinders.
    •    Cooling: Carries away heat from working components.
    •    Contamination control: Suspends dirt, sludge, and moisture until it’s filtered out.

2. Base Oils
    •    Mineral-based: Most common, refined petroleum with additives.
    •    Synthetic: Polyalphaolefins (PAO), esters, organophosphates; better stability, higher cost.
    •    Biodegradable: Esters or vegetable oils, used for environmentally sensitive sites.

3. Key Properties to Watch
    •    Viscosity & Viscosity Index (VI): Must match OEM spec; low VI means it thins out too fast with heat.
    •    Oxidation stability: Longer life, fewer varnish deposits.
    •    Anti-wear performance: Usually with zinc dialkyldithiophosphate (ZDDP) or ashless chemistry.
    •    Demulsibility: Ability to shed water.
    •    Air release & foam control: Trapped air kills performance.
    •    Pour point: Cold weather operability.

4. Types (ISO VG Grades & Performance Levels)
    •    ISO VG 32 / 46 / 68: Most common grades (numbers = viscosity in cSt at 40°C).
    •    HL: Basic hydraulic lubricants (no anti-wear).
    •    HM: Anti-wear type (most industrial applications).
    •    HV: High VI, better temperature range stability.
    •    HF: Fire-resistant fluids (water-glycol, phosphate esters).

5. Additives Package
    •    Anti-wear agents
    •    Rust & corrosion inhibitors
    •    Antioxidants
    •    Foam inhibitors
    •    Detergents/dispersants

6. Service Life & Failure Points
Hydraulic oil typically runs 2,000–5,000 hours before a change-out, depending on contamination, oxidation, and temperature. Failures usually come from:
    •    Overheating (>80°C speeds oxidation)
    •    Water ingress (rust, additive depletion)
    •    Air entrainment (foaming, cavitation)
    •    Dirt contamination (accelerates pump wear)