Chapter 6 Hydraulic Fluid - PBworks 6 The Energy ... Describe the various functions a hydraulic fluid performs in a fluid power system. Identify and explain the general properties

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Chapter 6Chapter 6

The Energy Transmitting MediumThe Energy Transmitting Medium

Hydraulic FluidHydraulic Fluid

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© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.3

ObjectivesObjectives

� Describe the various functions a hydraulic fluid

performs in a fluid power system.

� Identify and explain the general properties of a

liquid that would make it suitable as a hydraulic

fluid.

� Name and describe the general categories of

materials that are commonly used as hydraulic

fluids.


ObjectivesObjectives

� Explain the terms used to describe the basic

characteristics of hydraulic fluids.

� Explain procedures to follow for the selection

and performance monitoring of hydraulic fluids.

� Describe appropriate procedures for handling,

storage, and disposal of hydraulic fluid.

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Functions of a Hydraulic Functions of a Hydraulic Fluid Fluid

� Transmitting the energy to do the work of the

system is the primary function of liquid in a

hydraulic system


Functions of a Hydraulic Functions of a Hydraulic FluidFluid

� The fluid is just as important as any of the

hardware components

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Performance Characteristics Performance Characteristics of a Hydraulic Fluidof a Hydraulic Fluid

– Lubricating power

– Viscosity

– Viscosity stability

– Ability to operate in

cold temperatures

– Oxidation resistance

– Ability to separate

from water and dirt

– Resistance to foaming

– Fire resistance

�When selecting a fluid, consider its:



� Friction is the resistance to movement between

two surfaces in contact

� The amount of friction depends on:

– Roughness of the surfaces in contact

– Force pushing the surfaces together

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� Lubrication reduces friction between two

surfaces by placing a layer of liquid between

them

� A properly selected liquid produces a film that

separates the surfaces and allows them to freely

move past each other



� Lubrication reduces friction

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� A film of hydraulic oil fills irregularities in

contact surfaces



� Viscosity is the internal resistance to flow

of a liquid

� A liquid with the proper viscosity provides

a strong film that:

– Greatly reduces friction between the bearing

surfaces of component parts

– Provides a seal between those parts

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� A liquid with a high viscosity resists flow,

while one with low viscosity flows easily



� Fluid provides a seal between parts

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� Viscosity changes as temperature and

pressure of a liquid change

– Warm fluid flows easier than cold fluid

– Viscosity index is the rate of viscosity change

in relation to temperature change

– The higher the viscosity index number, the

lower the rate of viscosity change



� Pour point is the ability of a fluid to flow

when cold

– Important to consider if a hydraulic system is

exposed to cold weather

– Should be 20° Fahrenheit below the coldest-

expected ambient system operating temperature

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� Pour point is important in cold weather

Atlas Copco



� Oxidation rate of a hydraulic fluid is affected by:

– Temperature

– Air entrainment in the fluid

– Contact with metals used in the construction of a

system

– Contaminants, such as dirt and water, that enter a

system

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� Typical operating temperature range for

hydraulic fluid in the reservoir is 110°F to

140°F

� Operating the system in this temperature range

will result in an acceptable fluid service life



� Maintaining the proper

reservoir fluid temperature

is important

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� Petroleum-based fluids must have the

ability to easily separate from water

– Select a fluid that resists emulsification

– Drain accumulated water from the bottom of

the reservoir



� Water that enters a system having a water-

based fluid will modify the oil/additive/water

ratio

– The correct ratio is required to maintain proper

fluid viscosity and other critical properties

– Re-establishing the ratio requires fluid testing and

adjustment of the elements to their proper

proportions

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� Foaming increases fluid oxidation

– Caused by air being drawn into system inlet lines

or churned into reservoir fluid

– Increases air/fluid contact because of bubble

surface area



� The possibility of fire exists to some extent in

many hydraulic applications

– Petroleum-based fluids can supply adequate safety

levels in many systems

– Fire-resistant fluids using water or synthetic bases

are required when higher fire protection is needed

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Commonly UsedCommonly UsedHydraulic FluidsHydraulic Fluids

� Although water is readily available and

inexpensive, it is not used alone:

– Poor lubricant

– Promotes rust

– Freezes

– Rapidly evaporates at temperatures within the

operating range of many typical hydraulic systems



� Most common hydraulic fluid in use consists

of petroleum base blended with additives to

produce the desired operating properties

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� Biodegradable hydraulic fluids reduce the

harmful effects of fluid spills on soil and

waterways

� Biodegradable fluids are:

– Primarily vegetable-based oils

– Easily broken down by organisms found in nature



� Biodegradable fluids are important when

reducing environmental impact

Grayling Recreation Authority, Hanson Hills Recreation Area

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� Soluble-oil emulsion hydraulic fluids are

used in metal forging, extrusion equipment,

or other large applications

� Fluid designated as an oil-in-water emulsion

contains only 1% to 5% percent oil

– Extremely fire resistant

– Requires typical additives

– Subject to freezing



� Water-in-oil hydraulic fluids contain

approximately 60% oil and 40% water

– Limited anti-wear characteristics

– System operating pressures limited

– Has limited use because of instability and

maintenance needs

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� Fire-resistant hydraulic fluids will not burn

without sustained exposure to an ignition

source

– Water-oil emulsions

– Water-glycol fluids

– Synthetic fluids



� Water-in-oil emulsion fire-resistant fluids

contain approximately 40% water in an oil base

– Not to be confused with soluble-oil emulsions and

high-water-content fluids

– Called inverted emulsions because water is

suspended in oil, rather than oil in water

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� Water-glycol fire-resistant hydraulic fluids

usually contain 40% to 50% water with the

remainder a polyglycol

– Polyglycol is similar to automotive antifreeze

– Fluids adversely affect some seal materials and

paint



� All synthetic fluids provide excellent fire

resistance

� Phosphate esters are the most common

synthetic hydraulic fluids

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� All synthetic fluids meet the basic requirements

of a hydraulic fluid:

– Appropriate viscosity

– Good high-pressure performance

– Good lubrication



� Disadvantages of synthetic fluids include:

– Special seal material requirements

– Tendency to dissolve paint

– Environmental toxicity level must be carefully

considered before using in sensitive areas

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Hydraulic Fluid AdditivesHydraulic Fluid Additives

� Chemicals are used as additives in

hydraulic fluids to increase the stability

and overall performance of the fluid



� Extreme-pressure and anti-wear agents help

prevent metal-to-metal contact of bearing

surfaces to reduce friction and wear

� Viscosity-index improvers reduce changes in

viscosity as the fluid changes temperatures

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� Pour-point depressant allows the fluid to flow

freely at lower temperatures

� Pour point is especially important for fluids

used in systems that are exposed to winter

weather



� Pour point is the

temperature at

which a fluid no

longer moves

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� Oxidation of hydraulic fluids is caused by:

– Heat

– Exposure to air

– Catalytic effects of metal

� Oxidation-inhibitor additives reduce oxidation

of fluids



� Demulsifier additives increase the fluid’s

surface tension

– Promote separation of water from petroleum-based

fluids

– Any water that enters the system separates more

quickly from the oil

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� Antifoaming agents reduce surface tension

– Allow air bubbles to break down before a sufficient

quantity of foam is formed

– Foam causes operational problems in the system



� Rust and corrosion inhibitors protect the metal

parts of system components

– Rust inhibitors protect ferrous metals

– Corrosion inhibitors protect nonferrous metals

� Rust and corrosion inhibitors either:

– Neutralize acids

– Form a film on metal surfaces

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Hydraulic Fluid Hydraulic Fluid SpecificationsSpecifications

� Kinematic viscosity is a very precise measurement for indicating hydraulic fluid viscosity

� Test involves measuring the time required for a specific volume of fluid at a specified temperature to flow through a calibrated, glass capillary viscometer and then multiplying that value by a constant established for each instrument



� A calibrated, glass

capillary viscometer

is used to determine

kinematic viscosity

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� ISO outlines 20 viscosity grades

– Grades are based on kinematic viscosity tests

– Each grade can vary plus or minus 10% of stated

viscosity



� SAE outlines several petroleum product

viscosity grades

– Based on kinematic viscosity ratings

– Extensively used with automotive products

– Used with hydraulic fluids in the past, but less

commonly so today

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� Saybolt Universal Viscosity rating often used

to indicate hydraulic fluid viscosity

– Not currently supported by a standardizing

organization

– Does not truly relate to the standard definition of

viscosity, but allows comparisons of fluids

– Test involves measuring the time required for

60 ml of fluid at a specified temperature to flow

through a calibrated orifice



� Conducting a Saybolt Universal Viscosity test

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� Specific gravity and API gravity provide

comparisons between the weights of a volume

of a substance and an equal volume of distilled

water

– Specific gravity can be used with any material

– API system was developed primarily for petroleum

oils



� Distilled water has a

specific gravity of 1.0

� Distilled water has an

API gravity of 10.0

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� Pour point is 3°C above the temperature at

which movement can no longer be detected in

a fluid that has been cooled following an

established test procedure



� Flash point is the temperature at which the fluid

vapors form a flammable mixture with air

� Fire point is the temperature at which the fluid

is vaporizing rapidly enough to support

combustion

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� Flash and fire points

are important factors

for many applications



� A variety of ASTM standards provide test

specifications to establish rust-, corrosion-, and

oxidation-prevention capabilities of hydraulic

fluids

� These factors are critical to the service life of

system component parts and the fluid itself

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� Demulsibility and foaming characteristics of

hydraulic fluids may be determined by test

procedures detailed in ASTM specifications

� Results of these tests indicate the ability of a

hydraulic fluid to separate from water that

has entered the system and resist foam

formation when air is introduced through

components



� Lubricating and wear resistance characteristic

of hydraulic fluid can be evaluated by various

ASTM standards

– Some of these procedures use laboratory test

equipment to measure the protection provided to

metal parts by the liquid film formed by the fluid

– Other procedures measure the actual wear of

standard pump parts produced by controlled load

conditions

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Handling and Maintaining Handling and Maintaining Hydraulic FluidsHydraulic Fluids

� Proper handling and maintenance of

hydraulic fluids reduces system operating

cost

– Extends the service life of fluids

– Reduces the amount of maintenance time spent

in cleaning and flushing systems and replacing

system fluid



� Storing new, unused hydraulic fluids is an

important consideration

– Store drums in a cool, clean, dry place

– Place drums on their sides to reduce chances of

contamination

– Carefully clean drum tops before removing

bungs

– Use clean fluid-transfer equipment

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� Store drums on their

sides and clean the

tops before opening

the bungs



� Reservoir and cylinder rod areas are especially

susceptible to foreign materials entering the

system

– Seal around pipes entering the reservoir

– Filter air that enters the reservoir

– Use piston rod wiper rings or boots to prevent dirt

from entering through the cylinder rod seal

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� Cylinder rod boots help keep dirt out of the

system on rod retraction

A & A Manufacturing Co., Inc., Grotite



� System operating temperature is a major factor

in the service life of hydraulic fluids

� Normal operating temperature of reservoir fluid

is typically between 110°F and 140°F

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� Factors causing system fluid to operate above

the recommended temperature are:

– High ambient temperatures

– Reservoir is too small

– Reservoir inlets and outlets too close

– System pump has excessive flow capacity

– Higher-than-required relief valve setting

– Slower-than-necessary circuit sequencing



� A well-designed reservoir helps maintain

proper fluid temperature

Continental Hydraulics

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Review QuestionReview Question

The primary function of the liquid in a hydraulic system is to:

A.Clean system parts.

B.Remove heat from the system.

C. Transmit energy to do the work the system is

designed to complete.

D.Prevent rust and corrosion of system components.

C. Transmit energy to do the work the system

is designed to complete.



Name three major problems that may appear if

a fluid with too low of a viscosity is used in a

hydraulic system.

(any three)A. Increased system wear, B. increased

internal leakage, C. decreased pump efficiency and

control accuracy, and D. increased system operating

temperature.

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List the characteristics of water that make it a

poor hydraulic fluid should it be used alone in

a fluid power system.

A. Poor lubricating qualities, B. promotes

rust and corrosion, C. freezes within the

ambient temperature range of many systems,

and D. rapidly evaporates at higher system

operating temperatures.



The lowest temperature at which a liquid gives

off sufficient vapors to ignite when a flame is

applied is called the _____.

flash point

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Name three conditions in a fluid power system

that promote oxidation and general

deterioration of a hydraulic fluid.

(any three)A. High system operating

temperatures, B. entrainment of air in the fluid,

C. reactions caused by contact with different

metals used in the system, and D. contaminants

in the system, such as dirt and water.



Name three common ways that water can enter

a fluid power system and contaminate the

system fluid.

A. Condensation in the reservoir, B. water

sprayed on the equipment for cleaning

purposes, and C. exposure to weather in

exterior installations.

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GlossaryGlossary

� Additive

– A chemical compound added to a hydraulic fluid to modify its characteristics and improve system performance.

� Anti-wear agent

– A chemical compound added to hydraulic fluid to help reduce wear on bearing surfaces during hydraulic system operation.


GlossaryGlossary

� Biodegradable fluid

– A hydraulic fluid formulated to degrade in nature to reduce environmental damage from spillage.

� Capillary viscometer

– A test instrument containing a capillary tube calibrated to provide information adequate to determine the viscosity of fluid.

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GlossaryGlossary

� Emulsion– A stabilized mixture of oil and water that typically has a milky appearance. An example is fire-resistant hydraulic fluid, which is classified as oil-in-water or water-in-oil.

� Fire point– The lowest temperature at which a volatile substance vaporizes rapidly enough to produce an air-vapor mixture that will continuously burn when ignited.


GlossaryGlossary

� Fluid

– A substance such as air, water, or oil that easily

flows and tends to assume the shape of the

container in which it is stored.

� Friction

– The force that retards or resists the movement of

two touching materials.

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GlossaryGlossary

� HWCF

– High-water-content hydraulic fluids that are

primarily water with 2% to 5% soluble chemicals.

� Kinematic viscosity

– A precise indicator of the viscosity of a liquid. The

rating is based on the time required for a fixed

amount of a fluid to flow through a calibrated

viscometer under a fixed pressure and temperature.


GlossaryGlossary

� Oxidation inhibitors– Materials added to hydraulic fluids to slow the complex chemical reactions that oxidize the fluid.

� Phosphate ester– A synthetic hydraulic fluid that has a high flash point and provides excellent fire resistance.

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GlossaryGlossary

� Polyglycol

– A fluid similar in chemical makeup to automotive

antifreeze. Used in fire-resistant, water-glycol

hydraulic fluid.

� Pour point

– The lowest temperature at which a fluid will flow as

defined by a standardized test procedure.


GlossaryGlossary

� Rust inhibitor

– One of a group of additives used in hydraulic fluids

that are designed to protect metal parts by

neutralizing acids or forming a film on the metal

surfaces to protect them from damage.

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� Saybolt viscometer– A viscosity test apparatus that measures the number of seconds needed for a heated oil to drain through a calibrated orifice to fill a sample flask. No longer considered an accurate method of measuring viscosity.

GlossaryGlossary


GlossaryGlossary

� Specific gravity– The ratio of the weight of a given volume of a material to the weight of an equal volume of water at 4° Celsius.

� Viscosity– The internal resistance to flow of the molecules of a liquid.

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GlossaryGlossary

� Viscosity index number

– A number that expresses the relative change in

viscosity that can be expected for a given change in

temperature of a liquid.

Documents

Chapter 6 Hydraulic Fluid - PBworks 6 The Energy ... Describe the various functions a hydraulic fluid performs in a fluid power system. Identify and explain the general properties