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Jan 20, 2020


  • Flanagan Balling posted an update 6 months, 1 week ago

    Perhaps you have driven through an undesirable puddle water only to have your miserable engine lock solid after ingesting a cylinder full? This is what’s called hydraulic lock and it is a pricey illustration of hydraulic power which hydraulic oils convey.

    Within this commentary I’ll be emphasizing hydraulic fluids rather than brake fluids, that are a very specialized sub grouping.

    Functions and properties

    The crucial function of hydraulic oils is always to convey power. On the other hand, there are many significant functions of present hydraulic fluids.

    The table below lists the principle functions of hydraulic oil and the properties of the fluid that shape its capability to perform that function:

    Hydraulic Performance properties

    • Low compressibility (high bulk modulus)

    • Quick air release

    • Low foaming tendency

    • Low volatility

    Thermal performance

    • Good thermal function and conductivity

    Sealing properties

    • Adequate viscosity and viscosity index

    • Shear stability


    • Satisfactory viscosity for film maintenance

    • Low temperature fluidity

    • Thermal and oxidative stability

    • Hydrolytic stability / water tolerance

    • Purity and filterability

    • Demulsibility

    • Wear reduction characteristics

    • Corrosion control

    Pump efficiency

    • Appropriate viscosity to curtail internal leakage

    • Superior viscosity index

    Special requirements

    • Fire resistance

    • Friction modifiers

    • Radiation resistance

    Environmental impact properties

    • Low toxicity when new or decomposed

    • Biodegradability


    Dating back ancient Egypt the way of hydraulic fluid was water. It had been only in the 1920s that mineral oil turned used. It was due to oils inherent lubrication properties and performance at temperatures above the boiling reason for water. Today most hydraulic fluids depend on mineral oil base stocks and more recently synthetic alternatives.

    Current hydraulic oils can contain a wide range of substances, as well as: mineral oils, butanol, esters (e.g. phthalates, like DEHP, and adipates), polyalkylene glycols (PAG), phosphate esters (e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitors, etc.

    For environmentally hypersensitive applications, like farm tractors and marine dredging (high may be the results of an oil spill coming from a ruptured oil line), biodegradable hydraulic oils depending on rapeseed (Canola) vegetable oil may be used (often combined with tailored synthetic esters). Typically these oils can be obtained as ISO 32, ISO 46, and ISO 68 specification oils

    Other base stocks can be used specialty applications, including for fire resistance and extreme temperature applications. Examples embrace: glycol, esters, organophosphate ester, polyalphaolefin, propylene glycol, and silicone oils (For Brake fluids).

    Aircraft hydraulic systems

    As aircraft performance improved, so the force required to activate mechanical flight controls increased, and hydraulic systems were unveiled in ease pilot effort. Hydraulic power can also be used to start the auxiliary power unit (APU) for self-starting the aircraft’s main engines. While several aircraft equipped with the M61 family of cannon, exploit hydraulic power to drive the gun system, permitting reliable high rates of fire.

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