Hydraulic fluid - AbsoluteAstronomy.com

Hydraulic fluids, also called hydraulic liquids, are the medium by which power is transferred in hydraulic machinery

Hydraulic machinery

Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...

. Common hydraulic fluids are based on mineral oil

Mineral oil

A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....

or water. Examples of equipment that might use hydraulic fluids include excavator

Excavator

Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform . The house sits atop an undercarriage with tracks or wheels. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the...

s and backhoe

Backhoe

A backhoe, also called a rear actor or back actor, is a piece of excavating equipment or digger consisting of a digging bucket on the end of a two-part articulated arm. They are typically mounted on the back of a tractor or front loader...

s, brake

Brake

A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

s, power steering

Power steering

Power steering helps drivers steer vehicles by augmenting steering effort of the steering wheel.Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. Power steering helps considerably when a...

systems, transmissions

Transmission (mechanics)

A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

, garbage trucks, aircraft flight control systems, lift

Lift

Lift may mean:* Lift , a mechanical force generated by an object moving through a fluid* Lift , rising air used by soaring birds and glider, hang glider and paraglider pilots for soaring flight...

s, and industrial machinery.

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

Functions and properties

The primary function of a hydraulic fluid is to convey power. In use, however, there are other important functions of hydraulic fluid such as protection of the hydraulic machine components. The table below lists the major functions of a hydraulic fluid and the properties of a fluid that affect its ability to perform that function:

Function	Property
Medium for power transfer and control	Low compressibility (high bulk modulus) Fast air release Low foaming tendency Low volatility
Medium for heat transfer	Good thermal capacity and conductivity
Sealing Medium	Adequate viscosity Viscosity Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity... and viscosity index Viscosity index Viscosity index is an arbitrary measure for the change of viscosity with temperature. It is used to characterize lubricating oil in the automotive industry.... Shear stability
Lubricant	Viscosity for film maintenance Low temperature fluidity Thermal and oxidative stability Hydrolytic stability / water tolerance Cleanliness and filterability Demulsibility Antiwear characteristics Corrosion control
Pump efficiency	Proper viscosity to minimize internal leakage High viscosity index
Special function	Fire resistance Friction modifications Radiation resistance
Environmental impact	Low toxicity when new or decomposed Biodegradability Biodegradation Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means...
Functioning life	Material compatibility

Base stock

The original hydraulic fluid, dating back to the time of ancient Egypt

Ancient Egypt

Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

, was water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. Beginning in the 1920s, mineral oil

Mineral oil

A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....

began to be used more than water as a base stock due to its inherent lubrication

Lubrication

Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...

properties and ability to be used at temperatures above the boiling point

Boiling point

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

of water. Today most hydraulic fluids are based on mineral oil base stocks.

Natural oils such as rapeseed

Rapeseed

Rapeseed , also known as rape, oilseed rape, rapa, rappi, rapaseed is a bright yellow flowering member of the family Brassicaceae...

(also called canola

Canola

Canola refers to a cultivar of either Rapeseed or Field Mustard . Its seeds are used to produce edible oil suitable for consumption by humans and livestock. The oil is also suitable for use as biodiesel.Originally, Canola was bred naturally from rapeseed in Canada by Keith Downey and Baldur R...

oil) are used as base stocks for fluids where biodegradability and renewable sources are considered important.

Other base stocks are used for specialty applications, such as for fire resistance and extreme temperature applications. Some examples include: glycol, ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s, organophosphate ester, polyalphaolefin, propylene glycol

Propylene glycol

Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...

, and silicone

Silicone

Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....

oils.

Other components

Hydraulic fluids can contain a wide range of chemical compounds, including: oil

Oil

An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

s, butanol

N-Butanol

n-Butanol or n-butyl alcohol or normal butanol is a primary alcohol with a 4-carbon structure and the molecular formula C4H9OH. Its isomers include isobutanol, 2-butanol, and tert-butanol...

, esters (e.g. phthalates, like DEHP

Bis(2-ethylhexyl) phthalate

Bisphthalate, commonly abbreviated DEHP, is an organic compound with the formula C6H42. It is sometimes called dioctyl phthalate and abbreviated DOP. It is the most important "phthalate," being the diester of phthalic acid and the branched-chain 2-ethylhexanol. This colourless viscous liquid is...

, and adipate

Adipate

Adipate is the ionized form of adipic acid.As food additives, adipates are used as acidity regulators. Examples are sodium adipate and potassium adipate .-See also:* Acidity regulator...

s, like bis(2-ethylhexyl) adipate

Bis(2-ethylhexyl) adipate

Bis adipate or DEHA is a plasticizer. DEHA is an ester of 2-ethylhexanol and adipic acid. Its chemical formula is 22424.DEHA is sometimes called "dioctyl adipate", incorrectly. Other names include diisooctyl adipate and di adipate.-Use:DEHA is used as a functional hydraulic fluid, and a component...

), polyalkylene glycols (PAG), phosphate esters

Organophosphate

An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...

(e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitor

Corrosion inhibitor

A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy. The effectiveness of a corrosion inhibitor depends on fluid composition, quantity of water, and flow regime...

s, etc.

Biodegradable hydraulic fluids

Environmentally sensitive applications (e.g. farm tractors and marine dredging) may benefit from using biodegradable hydraulic fluids based upon rapeseed

Rapeseed

Rapeseed , also known as rape, oilseed rape, rapa, rappi, rapaseed is a bright yellow flowering member of the family Brassicaceae...

(Canola

Canola

) vegetable oil when there is the risk of an oil spill

Oil spill

An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...

from a ruptured oil line. Typically these oils are available as ISO

International Organization for Standardization

The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

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.

Brake fluid

Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer force into pressure...

is a subtype of hydraulic fluid with high boiling point

Boiling point

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

, both when new (specified by the equilibrium boiling point) and after absorption of water vapor (specified by wet boiling point). Under the heat of braking, both free water and water vapor in a braking system can boil into a compressible vapor, resulting in brake failure. Glycol-ether based fluids are hygroscopic, and absorbed moisture will greatly reduce the boiling point over time. Silicone based fluids are not hygroscopic, but their inferior lubrication is not suitable for all braking systems.

Safety

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

Fire resistance is a property available with specialized fluids.

Trade names

Some of the trade names for hydraulic fluids include Arnica

Arnica

Arnica is a genus with about 30 perennial, herbaceous species, belonging to the sunflower family . The genus name Arnica may be derived from the Greek arna, "lamb", in reference to the soft, hairy leaves....

, Tellus

Tellus

Tellus is a Latin word meaning "earth" and may refer to:* Terra or Terra Mater, the Roman Earth Mother goddess* Tellus , a citizen of ancient Athens who was thought to be the happiest of men...

, Durad, Fyrquel, Houghto-Safe, Hydraunycoil, Lubritherm Enviro-Safe, Pydraul, Quintolubric, Reofos, Reolube,Valvoline Ultramax and Skydrol

Skydrol

Skydrol is an advanced fire resistant aviation hydraulic fluid manufactured by Solutia Inc. There are various lines of Skydrol including Skydrol 500B-4, Skydrol LD-4, and Skydrol 5....

Aircraft hydraulic systems

As aircraft performance increased in mid-20th century, the amount of force required to operate mechanical flight controls became excessive, and hydraulic systems were introduced to reduce pilot effort. The hydraulic actuators are controlled by valves; these in turn are operated directly by input from the aircrew (hydro-mechanical) or by computers obeying control laws (fly by wire). See flight controls.

Hydraulic power is used for other purposes. 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

M61 Vulcan

The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...

family of cannon use hydraulic power to drive the gun system, permitting reliable high rates of fire.

The hydraulic power itself comes from pumps driven by the engines directly, or by electrically driven pumps. 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. This provides electrical power for the hydraulic pumps and control systems as power is no longer available from the engines. In that system and others electric pumps can provide both redundancy and the means of operating hydraulic systems without the engines operating, which can be very useful during maintenance.

Specifications

Aircraft hydraulic fluids fall under various specifications:

Common petroleum-based:

Mil-H-5606: Mineral base, flammable, fairly low flashpoint, usable from −65 F to 275 °F (135 °C), red color
Mil-H-83282: Synthetic hydrocarbon base, higher flashpoint, self-extinguishing, backward compatible to -5606, red color, rated to -40 F degrees.
Mil-H-87257: A development of -83282 fluid to improve its low temperature viscosity.

Phosphate-ester based:

There are no military specifications for Skydrol hydraulic fluids. The list below contains most of the existing industry specifications and approvals:

S.A.E. - AS1241
Boeing Seattle - BMS3-11
Boeing Long Beach - DMS2014
Lockheed - LAC C-34-1224
Airbus Industrie - NSA307110
British Aerospace - BAC M.333.B
Bombardier - BAMS 564-003

Below are some of the more common aircraft Phosphate-ester based hydraulic fluids.

Skydrol 500B-4 (Type IV class 2): The Skydrol 500 series of fluids has the longest service history among phosphate ester products. The first version, Skydrol 500, was introduced in 1952. Steady improvements to the formulation led in 1978 to the current version, Skydrol 500B-4 which contains the same breakthrough anti erosion additive and acid scavenger found in Skydrol LD-4 . Skydrol 500B-4 is the most worker friendly of the aviation phosphate esters; it is least irritating to skin and less prone to form mists which can be irritating to the respiratory tract . This has given the product enormous popularity for use in work shops and indoor test stands.

Skydrol LD-4 (Type IV class 1): Was also introduced in 1978, and is today the largest selling aviation phosphate ester fluid in the world. At the time of its introduction it was a breakthrough product, solving problems of valve erosion and thermal stability common in earlier fluids. Its excellent thermal stability under real world conditions has given it a reputation as the gold standard among Type IV fluids. In recent years it has received an additional qualification of 5000 psi approval under Boeing BMS 3-11 (Type V, Grade B and Grade C). Skydrol LD-4 features low density, excellent thermal stability, valve erosion prevention, and deposit control.

Skydrol 5 (Type V): Introduced in 1996, Skydrol 5 was the first Type V fluid qualified under the Boeing BMS 3-11 specification. Skydrol 5 offers higher temperature capability than Type IV fluids, the lowest density, and better paint compatibility. Skydrol 5 does not have universal air frame manufacturer approval.

Skydrol PE-5 (Type V): Skydrol PE-5, introduced in 2010, has full approval from Airbus and Boeing for use in all of their aircraft models. Skydrol PE-5 was developed to meet and exceed the more demanding Type V fluid requirements. It features the longest fluid life of any commercially available fluid, low density and low viscosity at low temperature; an unbeatable combination of the best features for optimum fluid performance.

Exxon
Exxon
Exxon is a chain of gas stations as well as a brand of motor fuel and related products by ExxonMobil. From 1972 to 1999, Exxon was the corporate name of the company previously known as Standard Oil Company of New Jersey or Jersey Standard....

HyJet IV-A plus (Type IV): Exxon HyJet IV-A plus is a fire-resistant phosphate ester hydraulic fluid designed for use in commercial aircraft. It is the best-performing Type IV fluid and approaches to a great extent many of the performance capabilities of Type V fluids, including high temperature stability,fluid life, low density, and rust protection. It is superior to all other Type IV fluids in these respects. Exxon HyJet IV-A plus meets the specifications of all major aircraft manufacturers and SAE AS1241.

Exxon Hyjet V (Type V): Exxon HyJet V is a Type V fire-resistant phosphate ester hydraulic fluid, which is superior in thermal and hydrolytic stability to commercially available Type IV hydraulic fluids. Better stability means the extent of fluid degradation in aircraft systems will be less than Type IV fluids, in-service fluid life will be longer, and aircraft operator maintenance costs will be lower. HyJet V provides excellent high and low temperature flow properties (kinematic viscosities) and rust protection. HyJet V has also demonstrated an improvement over the erosion protection performance afforded by Type IV fluids.

Contamination

Special, stringent care is required when handling aircraft hydraulic fluid as it is critical to flight safety that it stay free from contamination. It is also necessary to strictly adhere to authorized references when servicing or repairing any aircraft system. Samples from aircraft hydraulic systems are taken during heavy aircraft maintenance checks

Aircraft maintenance checks

Aircraft maintenance checks are periodic checks that have to be done on all aircraft after a certain amount of time or usage. Airlines and other commercial operators of large or turbine-powered aircraft follow a continuous inspection program approved by the Federal Aviation Administration in the...

to check contamination.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.