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What is the definition of bulk modulus?

A value that describes the compressibility of fluids. A high bulk modulus indicates low compressibility, while a low bulk modulus indicates high compressibility.
Learn more about bulk modulus in the class "Hydraulic Fluid Selection 320" below.

Hydraulic Fluid Selection 320

Hydraulics and Pneumatics Training

Class Information

Tooling U classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and typically requires at least two hours of instruction time.

Class Name:	Hydraulic Fluid Selection 320
Description:	This class provides an overview of the types of hydraulic fluid and the properties that make them ideal for certain applications. Includes an Interactive Lab.
Prerequisites:	570120 570140
Difficulty:	Advanced
Number of Lessons:	18

Below are all the competencies and job programs that contain the class Hydraulic Fluid Selection 320. Job programs are our traditional class lists organized according to common job functions. Competences are our latest job-specific curricula that help tie online learning to practical, hands-on tasks.

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Competencies
Fluid Power Specialist

Job Programs
Job: Maintenance and Repair: General Job: Maintenance and Repair: Industrial Machinery

Class Outline
Objectives Hydraulic Fluids Incompressibility and Bulk Modulus Viscosity Measuring Viscosity Viscosity Index Lubricity Resistance to Oxidation, Rust, and Corrosion Demulsibility and Foam Resistance Petroleum Oil Fire Resistance High-Water Fluids Water-in-Oil Emulsion Water-Glycol Synthetic Hydraulic Fluid Eco-Friendly Hydraulic Fluids Choosing a Hydraulic Fluid Summary

Class Objectives

Describe the role of fluid in a hydraulic system.
Define bulk modulus.
Define viscosity.
Describe different ways to measure viscosity.
Describe viscosity index.
Describe lubricity.
Distinguish between the effects of oxidation, rust, and corrosion.
Define demulsibility.
Describe types of petroleum crude.
Define temperature standards associated with fire resistance.
Define high-water fluid.
Describe a water-in-oil emulsion.
Describe a water-glycol hydraulic fluid.
Describe synthetic hydraulic fluids.
Describe eco-friendly hydraulic fluids.
Describe which fluids are ideal for a given situation.

Class Vocabulary
5-95 fluid		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.
absolute viscosity		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.
asperities		Microscopic peaks found on all surfaces. Contact between asperities on different surfaces causes friction.
auto-ignition temperature		The temperature at which the hydraulic fluid will combust spontaneously without exposure to a flame.
biodegradable		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.
boundary lubrication		A lubricating condition that occurs when the clearance between surfaces is pressed thin and asperities on both surfaces begin to touch.
bulk modulus		A value that describes the compressibility of fluids. A high bulk modulus indicates low compressibility, while a low bulk modulus indicates high compressibility.
capillary tube		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.
cavitation		An unwanted condition characterized by the formation of cavities on the surface of a metal hydraulic component. Cavitation is commonly caused by entrained air.
centipoise		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.
centistoke		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.
compressibility		The ability to be compressed by pressure. Gases have high compressibility, while liquids do not.
corrosion		A process by which a metal degrades from a reaction with a chemical such as an acid.
crude oil		Unrefined petroleum oil. Crude oil is the liquid petroleum that is pumped from the earth.
demulsibility		The resistance of a hydraulic fluid to emulsification, or how well a hydraulic fluid resists mixing with water.
dynamic viscosity		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.
efflux		Outward flow. The SUS viscosity is determined by timing the efflux of a hydraulic fluid.
emulsify		To mix two liquids together that do not usually mix well.
entrained		Trapped and suspended in hydraulic fluid.
ester		An organic compound formed by mixing an acid and alcohol.
fire point		The temperature at which the hydraulic fluid surface emits enough vapor to sustain a fire for five seconds in the presence of a flame.
flammability		The ability or tendency to ignite and burn when exposed to an open flame.
flash point		The temperature at which the hydraulic fluid surface emits enough vapor to ignite in the presence of a flame.
fluidity		A hydraulic fluid's ability to flow. As temperature increases, fluidity increases.
full-film lubrication		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.
glycol		A type of alcohol found in many commercial antifreeze products.
halogenated hydrocarbons		A chemical compound commonly used in synthetic hydraulic fluids.
heavy crude		A type of crude oil with high viscosity due to the presence of wax.
high water base fluid		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.
high water content fluid		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.
high-gravity crude		A type of crude oil characterized by low-density and low-specific gravity. High-gravity crude is also called thin crude.
high-water fluid		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.
hydraulic fluid		A liquid such as oil or water that is used to generate power in a hydraulic system.
incompressibility		The ability to resist compression by pressure. Liquids have high incompressibility, while gases do not.
incompressible		Relatively incapable of losing volume in response to pressure. Liquids are relatively incompressible, while gases are highly compressible.
International Organization for Standardization		ISO. An organization based in Switzerland that develops and publishes standards for its international membership base.
invert emulsions		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.
ISO grades		A viscosity classification system set by the International Organization for Standardization.
ISO HFA		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.
ISO HFB		The International Organization for Standardization classification for a water-in-oil emulsion, a fire-resistant hydraulic fluid consisting of 40% water and 60% oil.
ISO HFC		The International Organization for Standardization classification for a water-glycol hydraulic fluid, a fire-resistant hydraulic fluid consisting of water and glycol.
ISO HFD		The International Organization for Standardization classification for a synthetic hydraulic fluid.
kinematic viscosity		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.
light crude		A type of crude oil with low viscosity due to the relative absence of wax.
low-gravity crude		A type of crude oil characterized by high density and high-specific gravity. Low-gravity crude is also called thick crude.
lubricity		A general term used to describe a lubricant's effectiveness and ability to lubricate. An effective lubricant has a high lubricity.
neoprene		A lightweight synthetic material, similar to rubber, that is often used to make seals in a hydraulic system.
nitrile		A rubber-like material used to make seals that resist petroleum or oil compounds in a hydraulic system.
non-toxic		Not poisonous, harmful, or otherwise destructive to an organism upon exposure.
oil		A naturally occuring liquid hydrocarbon. Refined oil is the most common hydraulic fluid base.
oxidation		A chemical process in which a hydraulic fluid degrades due to a reaction with oxygen.
oxygen		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.
petroleum		Gaseous, liquid, or solid hydrocarbons naturally occuring beneath the earth's surface. Refined petroleum oil is the most common hydraulic fluid base.
phosphate esters		A chemical compound commonly used in synthetic hydraulic fluid. Phosphate esters are used in high-temperature applications.
polyglycol		A synthetic and biodegradable chemical used to make eco-friendly hydraulic fluids.
polyol esters		A chemical compound commonly used in synthetic hydraulic fluid. Polyol esters are known for stability at high temperatures.
pour point		The temperature at which a fluid begins to flow.
refining		The process of purifying crude oil to make it usable.
relative viscosity		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.
rust		A reddish-brown substance caused by metal's reaction with moisture and oxygen.
Saybolt Universal Seconds		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.
saybolt viscometer		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.
Society of Automotive Engineers		SAE. An organization of engineers that sets most industry standards for the testing, measuring, and designing of automobiles and their components.
sour crude		A type of crude oil with high sulphur content.
summer grade		An SAE viscosity classification system based on testing hydraulic fluids at 212°F (100°C).
SUS viscosity		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.
sweet crude		A type of crude oil with low sulphur content.
synthetic hydraulic fluid		A type of fire-resistant hydraulic fluid consisting of manmade chemicals. Synthetic fluids are classified as ISO HFD.
thick crude		A type of crude oil characterized by high density and high-specific gravity. Thick crude is also called low-gravity crude.
thin crude		A type of crude oil characterized by low-density and low-specific gravity. Thin crude is also called high-gravity crude.
viscosity		A hydraulic fluid's resistance to flow. As temperature increases, viscosity decreases.
viscosity index		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.
water-glycol		A fire-resistant hydraulic fluid consisting of water and glycol, a type of alcohol found in many commercial antifreeze products.
water-in-oil emulsion		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.
winter grade		An SAE viscosity classification system based on testing hydraulic fluids at cold temperatures.