Hydraulic fluid
A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in
Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has zero 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:[2]
Function | Property |
---|---|
Power transmission and control medium |
|
Medium for heat transfer |
|
Sealing medium |
|
Lubricant |
|
Pump efficiency |
|
Special function |
|
Environmental impact |
|
Functioning life |
|
Composition
Base stock
The original hydraulics fluid, dating back to the time of ancient Egypt, was water.[citation needed] Beginning in the 1920s, mineral oil began to be used more than water as a base stock due to its inherent lubrication properties and ability to be used at temperatures above the boiling point of water. Today most hydraulic fluids are based on mineral oil base stocks.
Natural oils such as
Other base stocks are used for specialty applications, such as for
Other components
Hydraulic fluids can contain a wide range of chemical compounds, including:
Biodegradable hydraulic fluids
Environmentally sensitive applications (e.g.
Anti-wear hydraulic fluids
Anti-wear (AW) hydraulic oils are made from a petroleum base fluid and commonly contain the anti-wear additive Zinc dialkyldithiophosphate (ZDDP). This additive works to protect the hydraulic pump. They come in multiple viscosity grades that have varying applications. For example, AW 46 hydraulic oils can be used to operate the hydraulic systems in off-road equipment such as dump trucks, excavators, and backhoes, while AW 32 hydraulic oils may be more suitable for colder weather applications like in a snow plow's pump.[4]
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.[5]
Fire resistance is a property available with specialized fluids. Water-glycol and polyol-ester are some of these specialized fluids that contain excellent thermal and hydrolitic properties, which aid in fire resistance.[6]
Uses
Brake fluid
Power steering fluid
Use of the wrong type of fluid can lead to failure of the power steering pump.[8]
Aircraft hydraulic systems
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. 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).
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 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
Specifications
Mineral oil base
According to DIN 51502
- HL: With agents to enhance corrosion protection and age resistance. Used in hydraulic systems that do not pose any requirements as to wear protection.
- HLP: With agents to enhance corrosion protection and age resistance. Suitable for most fields of application and components.
- HLPD: As HLP but also used in systems where solid or liquid contamination need to be kept temporarily suspended.
- HVLP: With agents to enhance corrosion protection, age resistance, to reduce scuffing wear in mixed friction areas, and to improve the viscosity-temperature behavior. Used in system operated over a wide temperature range.
- HVLPD: As HVLP but also used in systems where solid or liquid contamination need to be kept temporarily suspended.
According to MIL for military applications
Source:[11]
- Mil-PRF-5606 (originally Mil-H-5606): Mineral base, flammable, fairly low flashpoint, usable from −65 °F (−54 °C) to 275 °F (135 °C), red color, developed in the 1940s[13]
- MIL-PRF-6083: Usable from −54 °C to 135 °C "where corrosion protection is required and a determination has been made that MIL-PRF-46170 (FRH) hydraulic fluid cannot be used. This includes use in recoil mechanisms and hydraulic systems for rotating weapons or aiming devices of tactical and support ordnance equipment, except combat armored vehicles/equipment which require FRH. The hydraulic fluid is also used as a preservative fluid for aircraft hydraulic systems and components where MIL-H-5606 (OHA) or MIL-PRF-87257 is used as an operational fluid."[14]
Synthetic hydrocarbon base: These synthetic fluids are compatible with mineral-base hydraulic fluids and were developed to address the low flash point draw back of mineral based hydraulic fluids.[13]
- Mil-H-83282: Synthetic hydrocarbon base, higher flashpoint, self-extinguishing, backward compatible to -5606, red color, rated to −40 °F (−40 °C) degrees.
- Mil-H-87257: A development of -83282 fluid to improve its low temperature viscosity.
Multi purpose oil UTTO/STOU
- UTTO: Is an abbreviation for "Universal Tractor Transmission Oil". It is a hydraulic oil that can also be used in the transmissions and wet brakes of machines like tractors.
- STOU: Is an abbreviation for "Super Tractor Oil Universal". It is a hydraulic oil that can also be used in the motor, the transmissions and wet brakes. So its main difference to the UTTO oil is that it can be used also as an motor oil.
Phosphate-ester base
- US/NATO Military specification - MIL-H-8446
- Boeing Seattle - BMS3-11
- Boeing Long Beach - DMS2014
- Boeing Long Island - CDS5478
- Lockheed - LAC C-34-1224
- Airbus Industrie - NSA307110
- British Aerospace - BAC M.333.B
- Bombardier - BAMS 564-003
- SAE - Ac974
- SAE - AS1241
- Skydrol
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 (primarily C and D checks) to check contamination.[16]
Military Spec 1246C is one fluid contamination specification.
The ISO fluid contamination scale assigns a contamination category based on particle size count and distribution.[17]
Other uses
The properties of HLP 32 hydraulic oil make it ideal for lubricating machine tools.[18][19]
See also
- Dexron
- Hydraulic brake
- Hydraulic fuse
- Hydraulics International, INC.
- Hydropneumatic suspension - automobile application
- Oleo strut - aircraft application
- Osmosis
- Skydrol
References
- ISBN 0-8031-2096-6
- ISBN 1-57444-723-8
- ISBN 9780768009132. Retrieved 3 May 2017 – via Google Books.
- ^ What Does AW Stand For? - Petroleum Service Company
- ^ Labor, Carl (21 July 2022). "Is Hydraulic Fluid Flammable?". Safetyfirst. Retrieved 30 October 2022.
- ^ Peter, Skoog. "The Changing Economics of Fire-resistant Hydraulic Fluids" (PDF). Quaker Chemical Corporation. Retrieved 12 December 2014.
- ^ "DOT Brake Fluid vs. Mineral Oil - and the Winner is." EpicBleedSolutions.com. Retrieved 3 May 2017.
- ^ a b "Power Steering Fluid". www.AA1car.com. Retrieved 3 May 2017.
- ^ "Basic Composition of ATF" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2015-05-27.
- ^ Discovery channel-'seconds from disaster'
- ^ a b c Bosch Rexroth AG (2023). "Hydraulic fluids based on mineral oil and related hydrocarbons" (PDF). www.etshydro.com. Retrieved 2023-10-19.
- ^ Wodoil GmbH (2023-08-03). "Hydrauliköl für Ihren Holzspalter: Ein umfassender Leitfaden". Wodoil GmbH (in German). Retrieved 2023-10-19.
- ^ a b "Archived copy" (PDF). Archived from the original (PDF) on 2016-03-04. Retrieved 2017-02-25.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ "MIL-PRF-6083". QCLubricants.com. Retrieved 3 May 2017.
- ^ Wodoil Gmbh (2023-08-16). "Alles was Sie über STOU und UTTO Öle wissen müssen". Wodoil GmbH (in German). Retrieved 2023-10-19.
- ^ "A SUMMARY OF CONTAMINATION IN HYDRAULIC FLUID SYSTEMS OF USAF AND SUPPORT SYSTEMS".
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ "Hydraulic Contamination and Fluid Cleanliness in Power Units". FlyTek GSE. 2017-04-24. Retrieved 2023-06-20.
- ^ "Oil You Need To Know About Hydraulic Oils - Crown Oil". www.crownoil.co.uk.
- ^ "Machine-tool Lubrication". www.lathes.co.uk.
External links
This article's use of external links may not follow Wikipedia's policies or guidelines. (May 2017) |
- Information and purchase of military specification (mil-spec) hydraulic fluid
- Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
- USDA Research. Biodegradable Plant-Based Hydraulic Fluid
- Biodegradable Hydraulic Oils
- Industrial Hydraulic Oils
- Aviation hydraulic fluids