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Jan 28, 2020


  • Flanagan Balling posted an update 6 months, 2 weeks ago

    Perhaps you have travelled into a bad puddle water simply to have your miserable engine lock solid after ingesting a cylinder full? This is called hydraulic lock and is also a costly demonstration of hydraulic power which hydraulic oils convey.

    In this commentary I’ll be focusing on hydraulic fluids in contrast to brake fluids, which are a really specialized sub grouping.

    Functions and properties

    The crucial function of hydraulic oils would be to convey power. However ,, there are more significant functions of present hydraulic fluids.

    The table below lists the main functions of hydraulic oil as well as the properties from the fluid that shape its capacity 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


    Going back to ancient Egypt the mode for hydraulic fluid was water. It was only inside the 1920s that mineral oil has become used. It was as a result of oils inherent lubrication properties and performance at temperatures above the boiling point of water. Today most hydraulic fluids depend on mineral oil base stocks plus much more recently synthetic alternatives.

    Current hydraulic oils can have a massive amount substances, in addition to: 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, including farm tractors and marine dredging (where there will be the results of an oil spill coming from a ruptured oil line), biodegradable hydraulic oils according to rapeseed (Canola) vegetable oil can be used (often blended 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 for specialty applications, including for fire resistance and extreme temperature applications. A few examples embrace: glycol, esters, organophosphate ester, polyalphaolefin, propylene glycol, and silicone oils (For Brake fluids).

    Aircraft hydraulic systems

    As aircraft performance improved, therefore the force required to activate mechanical flight controls increased, and hydraulic systems were brought to 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 built with the M61 category of cannon, exploit hydraulic power to drive the gun system, permitting reliable high rates of fire.

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