Hydraulic fluid

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Hydraulic fluids are a large group of liquids made of many kinds of chemicals. They are used in automobile automatic transmissions, brakes, and power steering; forklift trucks; tractors; bulldozers; industrial machinery; and aircraft. The three most common types of hydraulic fluids are mineral oil, organophosphate ester, and polyalphaolefin. Others are based on glycol esters and ethers, castor oil, or silicone. Some of the trade names for hydraulic fluids include Durad®, Fyrquel®, Skydrol®, Houghton-Safe®, Pydraul®, Reofos®, Reolube®, Hydraunycoil®, and Quintolubric®.

Environmentally sensitive applications (e.g. farm tractors and marine dredging) may benefit from using biodegradable hydraulic fluids based upon rapeseed (Canola) vegetable oil when there is the risk of an oil spill from a ruptured oil line. Typically these oils are available as ISO 32, ISO 46, and ISO 68 specification oils. ASTM standards ASTM-D-6006, Guide for Assessing Biodegradability of Hydraulic Fluids and ASTM-D-6046, Standard Classification of Hydraulic Fluids for Environmental Impact are relevant. 2004 prices were about $25/gallon in small quantities.

Brake fluid is a subtype of hydraulic fluid with high boiling point and low freezing point.

Hydraulic systems, like the ones mentioned above, will work efficiently if the hydraulic fluid used has low compressibility.

Some hydraulic fluids have a bland, oily smell and others have no smell; some will burn and some will not burn. Certain hydraulic fluids are produced from crude oil and others are manufactured by many companies.

Hydraulic fluids can contain a wide range of various chemical compounds; oils, butanol, esters (e.g. phthalates, like DEHP, and adipates, like bis(2-ethylhexyl) adipate), polyalkylene glycols (PAG), phosphate esters (e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitors, etc.

It was reported that 3,800 patients of the Duke University Health System in Durham and Raleigh were operated on in late 2004 with instruments that were washed in PAG (polyalkylene glycol) hydraulic fluid 32-AW instead of detergent. This occurred after an elevator company drained hydraulic fluid into empty Mon-Klenz detergent barrels, and the detergent supplier redistributed them as detergent; both substances are similar in appearance, similar to maple syrup. The problem was not fixed for weeks in spite of the fact that staff members complained that the tools were "slick"; however a small amount of lubricant is commonly applied to them, as a corrosion protection and to protect the instruments from locking up, therefore it took some time to figure out the oiliness is beyond normal level. The hospital claims that there are no risks associated with the mix-up; however, patients have reported lingering health concerns. [1] [2]

Because industrial hydraulic systems operate at thousands of PSI and temperatures reaching several hundred degrees fahreneheit, severe injuries and death can result from component failures and care must always be taken when performing maintenance on hydraulics.