Hydraulic fluid

NaK-77, a eutectic alloy of sodium and potassium, can be used as a hydraulic fluid in high-temperature and high-radiation environments, for temperature ranges of 10 to 1400 °F (-12 to 760 °C).

[3] Hydraulic fluids can contain a wide range of chemical compounds, including: oils, butanol, esters (e.g. phthalates, like DEHP, and adipates, like bis(2-ethylhexyl) adipate), polyalkylene glycols (PAG), organophosphate (e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitors (incl acid scavengers), anti-erosion additives, etc.

Water-glycol and polyol-ester are some of these specialized fluids that contain excellent thermal and hydrolitic properties, which aid in fire resistance.

[7] Glycol-ether based fluids are hygroscopic, and absorbed moisture will greatly reduce the boiling point over time.

[8] As aircraft performance increased in the mid-20th century, the amount of force required to operate mechanical flight controls became excessive, and hydraulic systems were introduced to reduce pilot effort.

It can be stored in accumulators to start an auxiliary power unit (APU) for self-starting the aircraft's main engines.

Many aircraft equipped with the M61 family of cannon use hydraulic power to drive the gun system, permitting reliable high rates of fire.

In modern commercial aircraft these are electrically-driven pumps; should all the engines fail in flight the pilot will deploy a propeller-driven electric generator called a Ram-Air Turbine (RAT) which is concealed under the fuselage.

Special, stringent care is required when handling aircraft hydraulic fluid, as it is critical to flight safety that it stay free from contamination.

The most prevalent grades for general industrial and mobile hydraulic systems are typically: Additional viscosities such as the following, are also used, but less frequently or for specific low/high-temperature applications.