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5-95 fluid
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A fire-resistant hydraulic fluid consisting of 90-95% water and 5-10% oil or a similar synthetic solution. High-water fluids are also known as ISO HFA, high water base fluid, high water content fluid, and high-water fluid.
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absolute viscosity
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The resistance to flow encountered when one layer or plane of fluid attempts to move over another identical layer or plane of fluid at a given speed. Absolute viscosity is also called dynamic viscosity.
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asperities
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Microscopic peaks found on all surfaces. Contact between asperities on different surfaces causes friction.
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auto-ignition temperature
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The temperature at which the hydraulic fluid will combust spontaneously without exposure to a flame.
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biodegradable
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Capable of being broken down and naturally absorbed into the ecosystem. Biodegradable materials degrade into simple stable compounds that are not harmful to the environment.
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boundary lubrication
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A lubricating condition that occurs when the clearance between surfaces is pressed thin and asperities on both surfaces begin to touch.
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bulk modulus
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A value that describes the compressibility of fluids. A high bulk modulus indicates low compressibility, while a low bulk modulus indicates high compressibility.
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capillary tube
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A device used to measure kinematic viscosity. Kinematic viscosity is the time it takes for a fixed amount of fluid to move through a measured length of the capillary tube with gravity alone.
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cavitation
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An unwanted condition characterized by the formation of cavities on the surface of a metal hydraulic component. Cavitation is commonly caused by entrained air.
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centipoise
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A unit of measurement for absolute viscosity equal to one-hundredth of a poise. One centipoise is equal to the millipascal second, one-thousandth of a pascal second.
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centistoke
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A unit of measurement for kinematic viscosity equal to the unit millimeters squared per second. The centistoke is the ratio of a liquid's absolute viscosity in centipoise to the density.
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compressibility
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The ability to be compressed by pressure. Gases have high compressibility, while liquids do not.
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corrosion
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A process by which a metal degrades from a reaction with a chemical such as an acid.
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crude oil
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Unrefined petroleum oil. Crude oil is the liquid petroleum that is pumped from the earth.
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demulsibility
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The resistance of a hydraulic fluid to emulsification, or how well a hydraulic fluid resists mixing with water.
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dynamic viscosity
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The resistance to flow encountered when one layer or plane of fluid attempts to move over another identical layer or plane of fluid at a given speed. Dynamic viscosity is also called absolute viscosity.
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efflux
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Outward flow. The SUS viscosity is determined by timing the efflux of a hydraulic fluid.
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emulsify
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To mix two liquids together that do not usually mix well.
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entrained
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Trapped and suspended in hydraulic fluid.
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ester
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An organic compound formed by mixing an acid and alcohol.
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fire point
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The temperature at which the hydraulic fluid surface emits enough vapor to sustain a fire for five seconds in the presence of a flame.
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flammability
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The ability or tendency to ignite and burn when exposed to an open flame.
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flash point
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The temperature at which the hydraulic fluid surface emits enough vapor to ignite in the presence of a flame.
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fluidity
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A hydraulic fluid's ability to flow. As temperature increases, fluidity increases.
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full-film lubrication
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A lubricating condition that occurs when two contacting surfaces have a distinct film between them. The film provides clearance that completely separates the two surfaces.
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glycol
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A type of alcohol found in many commercial antifreeze products.
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halogenated hydrocarbons
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A chemical compound commonly used in synthetic hydraulic fluids.
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heavy crude
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A type of crude oil with high viscosity due to the presence of wax.
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high water base fluid
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A fire-resistant hydraulic fluid consisting of 90-95% water and 5-10% oil or a similar synthetic solution. High water base fluids are also known as ISO HFA, high-water fluid, high water content fluid, and 5-95 fluid.
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high water content fluid
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A fire-resistant hydraulic fluid consisting of 90-95% water and 5-10% oil or a similar synthetic solution. High-water content fluids are also known as ISO HFA, high water base fluid, high-water fluid, and 5-95 fluid.
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high-gravity crude
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A type of crude oil characterized by low-density and low-specific gravity. High-gravity crude is also called thin crude.
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high-water fluid
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A fire-resistant hydraulic fluid consisting of 90-95% water and 5-10% oil or a similar synthetic solution. High-water fluids are also known as ISO HFA, high water base fluid, high water content fluid, and 5-95 fluid.
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hydraulic fluid
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A liquid such as oil or water that is used to generate power in a hydraulic system.
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incompressibility
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The ability to resist compression by pressure. Liquids have high incompressibility, while gases do not.
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incompressible
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Relatively incapable of losing volume in response to pressure. Liquids are relatively incompressible, while gases are highly compressible.
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International Organization for Standardization
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ISO. An organization based in Switzerland that develops and publishes standards for its international membership base.
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invert emulsions
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A fire-resistant hydraulic fluid consisting of 40% water and 60% oil. Invert emulsions are classified as ISO HFB and are also called water-in-oil emulsions.
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ISO grades
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A viscosity classification system set by the International Organization for Standardization.
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ISO HFA
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The International Organization for Standardization classification for high-water fluid, a fire-resistant hydraulic fluid consisting of 90-95% water and 5-10% oil or a similar synthetic solution.
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ISO HFB
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The International Organization for Standardization classification for a water-in-oil emulsion, a fire-resistant hydraulic fluid consisting of 40% water and 60% oil.
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ISO HFC
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The International Organization for Standardization classification for a water-glycol hydraulic fluid, a fire-resistant hydraulic fluid consisting of water and glycol.
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ISO HFD
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The International Organization for Standardization classification for a synthetic hydraulic fluid.
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kinematic viscosity
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The ratio of a fluid's absolute viscosity to its density, or the absolute viscosity divided by the density. Kinematic viscosity is the most common viscosity measurement.
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light crude
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A type of crude oil with low viscosity due to the relative absence of wax.
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low-gravity crude
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A type of crude oil characterized by high density and high-specific gravity. Low-gravity crude is also called thick crude.
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lubricity
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A general term used to describe a lubricant's effectiveness and ability to lubricate. An effective lubricant has a high lubricity.
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neoprene
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A lightweight synthetic material, similar to rubber, that is often used to make seals in a hydraulic system.
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nitrile
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A rubber-like material used to make seals that resist petroleum or oil compounds in a hydraulic system.
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non-toxic
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Not poisonous, harmful, or otherwise destructive to an organism upon exposure.
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oil
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A naturally occuring liquid hydrocarbon. Refined oil is the most common hydraulic fluid base.
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oxidation
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A chemical process in which a hydraulic fluid degrades due to a reaction with oxygen.
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oxygen
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A colorless, tasteless, odorless gas that is roughly 20 percent of Earth's atmosphere. Oxygen can damage hydraulic fluids and components if not addressed in a hydraulic system.
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petroleum
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Gaseous, liquid, or solid hydrocarbons naturally occuring beneath the earth's surface. Refined petroleum oil is the most common hydraulic fluid base.
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phosphate esters
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A chemical compound commonly used in synthetic hydraulic fluid. Phosphate esters are used in high-temperature applications.
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polyglycol
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A synthetic and biodegradable chemical used to make eco-friendly hydraulic fluids.
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polyol esters
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A chemical compound commonly used in synthetic hydraulic fluid. Polyol esters are known for stability at high temperatures.
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pour point
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The temperature at which a fluid begins to flow.
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refining
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The process of purifying crude oil to make it usable.
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relative viscosity
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A value derived from timing the efflux of a fixed amount of hydraulic fluid as it moves through a standard-sized orifice at a fixed temperature. Relative viscosity is also called SUS viscosity.
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rust
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A reddish-brown substance caused by metal's reaction with moisture and oxygen.
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Saybolt Universal Seconds
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A unit of measurement for SUS, or relative, viscosity. Saybolt Universal Seconds are the number of seconds it takes for a fixed amount of hydraulic fluid to move through a standard-sized orifice at a fixed temperature.
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saybolt viscometer
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A device used to measure the viscosity of a fluid. The saybolt viscometer controls the heat of the fluid and the viscosity is the time is takes the fluid to fill a 60cc container.
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Society of Automotive Engineers
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SAE. An organization of engineers that sets most industry standards for the testing, measuring, and designing of automobiles and their components.
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sour crude
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A type of crude oil with high sulphur content.
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summer grade
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An SAE viscosity classification system based on testing hydraulic fluids at 212°F (100°C).
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SUS viscosity
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A value derived from timing the efflux of a fixed amount of hydraulic fluid as it moves through a standard-sized orifice at a fixed temperature. SUS viscosity is also called relative viscosity.
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sweet crude
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A type of crude oil with low sulphur content.
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synthetic hydraulic fluid
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A type of fire-resistant hydraulic fluid consisting of manmade chemicals. Synthetic fluids are classified as ISO HFD.
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thick crude
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A type of crude oil characterized by high density and high-specific gravity. Thick crude is also called low-gravity crude.
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thin crude
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A type of crude oil characterized by low-density and low-specific gravity. Thin crude is also called high-gravity crude.
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viscosity
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A hydraulic fluid's resistance to flow. As temperature increases, viscosity decreases.
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viscosity index
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A number describing how the viscosity of a fluid changes with temperature. Fluids affected by temperature extremes have a low viscosity index, while fluids that maintain viscosity have a high viscosity index.
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water-glycol
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A fire-resistant hydraulic fluid consisting of water and glycol, a type of alcohol found in many commercial antifreeze products.
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water-in-oil emulsion
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A fire-resistant hydraulic fluid consisting of 40% water and 60% oil. Water-in-oil emulsions are classified as ISO HFB and are also called invert emulsions.
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winter grade
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An SAE viscosity classification system based on testing hydraulic fluids at cold temperatures.
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