HYDRAULICS & PNEUMATICS Presented by: Dr. Abootorabi Hydraulic Fluids 1.

HYDRAULICS & PNEUMATICS

Presented by: Dr. Abootorabi

Hydraulic Fluids

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Task for hydraulic fluids

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Performance Characteristics of 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:

The most important distinguishing feature of hydraulic fluids is viscosity.3


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. 4


Viscosity is the internal resistance to flow of a liquid

(resistance to flow).

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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

Viscosity Viscosity may be the most important property of a

hydraulic fluid.

If the viscosity is too high, it may results in:

1. High resistance to flow, causing sluggish operation

2. Increased power consumption due to frictional losses

3. Increased pressure drop through valves and lines

4. High temperature due to friction6

On the other hand, if the viscosity is too low, it may result in:

1. Increased oil leakage past seals

2. Excessive wear due to breakdown of the oil film between

mating parts

There are two kinds of viscosity: Absolute viscosity (μ) and

kinematic viscosity (ν).

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Viscosity

Viscosity & Temperature

Hydraulic oils is directly affected by changes in

temperature.

For this reason, machinery should not be put into high

speed or heavily loaded operation until the system fluid is

warmed up to operating temperatures to provide

adequate lubrication.

Viscosity changes as temperature and pressure of a liquid

change. Warm fluid flows easier than cold fluid.8

Viscosity – temperature diagram

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Viscosity – pressure characteristics

At approx. 350 to 400 bar the viscosity is generally already double that at 0 bar.

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Viscosity IndexViscosity 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.

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Pour point is the ability of a fluid to flow when cold and:

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.


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.

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Normal operating temperature range for

hydraulic fluid in the reservoir is

typically 110°F to 140°F (43°C to 60°C) .

Operating the system in this

temperature range will result in an

acceptable fluid service life.

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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 are too close

System pump has excessive flow capacity

Higher-than-required relief valve setting

Slower-than-necessary circuit sequencing 15


A well-designed reservoir helps maintain proper fluid temperature.

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Performance Characteristics of a Hydraulic FluidDemulsibility is the ability of a fluid to separate out or

reject water.

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 periodically to prevent re-emulsification

and/or reaction with the fluid chemistry17


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

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Performance Characteristics of a Hydraulic FluidThe 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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Fire ResistanceFluid used in hydraulic systems must have fire resistant

properties.

Most fluids can be ignited under the right conditions

Fire resistant fluid will not sustain combustion when an

ignition source is removed

Fire resistant fluid will not allow flame to flash back to the

ignition source

It is important to analyze the working environment of the

specific application to determine fire hazards.

Some fluids may continue to burn after the ignition

source is removed21

Types of hydraulic fluid1. Hydraulic oils (divided into 3 classes according to DIN

51524 and 51525)

HL

HLP

HV

2. Hydraulic fluids with low inflammability

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Example:

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Most common hydraulic fluid in use consists of petroleum

base blended with additives to produce the desired operating

properties.

1. Hydraulic oils

Types of hydraulic fluid

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VDMA:

The VDMA (Verband Deutscher Maschinen- und Anlagenbau -

German Engineering Federation) is one of the key association

service providers in Europe and offers the largest engineering

industry network in Europe.

Types of hydraulic fluid2. Hydraulic fluids with low inflammability

Hydraulic fluids with low flammability Fire-resistant hydraulic fluids will not burn without

sustained exposure to an ignition source.

Oil-water (soluble oil emulsions)

Water-oil emulsions

Water-glycol fluids

Synthetic fluids

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– Hard coal mining

– Die-casting machines

– Control units for

power station

turbines

Applications:

– Steel works and rolling

mills

– Automotive

manufacture

– Offshore industry

– On aircraft and ships

Hydraulic fluids with low flammability

Oil-water (soluble oil emulsions) hydraulic fluids are used

in metal forging, extrusion equipment, or other large

applications.

Fluid designated as an oil-in-water emulsion commonly

contains only 1% to 5% oil:

Extremely fire resistant

Requires typical additives

Subject to freezing

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Water-in-oil emulsion fire-resistant fluids contain

approximately 40% water in an oil base.

Not to be confused with soluble-oil emulsions or high-

water-content fluids (oil-water emulsions)

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Called inverted emulsions because water is suspended in

oil, rather than oil in water

Limited anti-wear characteristics

System operating pressures limited

Has limited use because of instability and maintenance

needs


Water-glycol fire-resistant hydraulic fluids usually contain

40% to 50% water with the remainder of a polyglycol.

Polyglycol is similar to automotive antifreeze

An additive is added for improving the viscosity

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All synthetic fluids provide excellent fire resistance. These are not

water based.

Phosphate ethers 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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Water???

Although water is readily available and inexpensive, it is not

used alone:

Poor lubricant

Promotes rust and corrosion

Low viscosity

Freezes

Rapidly evaporates at temperatures within the operating

range of many typical hydraulic systems31

Another type of hydraulic fluidsBiodegradable hydraulic fluid 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

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Biodegradable fluids are

important when reducing

environmental impact.

Selection of fluidsThe fluid supplier must understand the nature of the fluid

application:

Environment

Types of components and their manufacture’s specifications

relative to fluids

Duty cycles

Loads (pressure)

Storage ability

Temperature extremes

Any unusual or special considerations in the operation of the

machinery that could affect the life of the fluid or its performance

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Hydraulic Fluid Additives

Chemicals are used as additives in hydraulic fluids to

increase the stability and overall performance of the fluid.

An inhibitor is any substance that slows or prevents chemical

reactions, such as corrosion or oxidation.

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Some common additives and inhibitors:

anti-wear additives, antifoam agent, corrosion inhibitor,

demulsifier, extreme pressure (EP) additive, oxidation

inhibitor, pour point depressant, rust inhibitor, Viscosity-

index improvers .

Hydraulic Fluid Additives Three types of anti-wear additives:

Anti-wear (AW) form a protective film on the metal

surface when exposed to low frictional heat

Wear resistant (WR) protects the rubbing surfaces

against wear, particularly from scuffing

Extreme pressure (EP) Either prevent surfaces from

coming into contact with one another or prevent surfaces from welding to one another when expose to high frictional heat

Use when operating at pressures >3000 psi (or 200 bar) 35

Hydraulic Fluid Additives

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

Antifoaming agents reduce surface tension:

Allow air bubbles to break down before a sufficient

quantity of foam is formed

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Hydraulic Fluid Additives It’s extremely difficult to keep air and moisture out of hydraulic

systems.

Corrosion is a chemical reaction between a metal and a chemical-

typically an acid.

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 37

Rust & Corrosion inhibitors

Rust inhibitors typically coat metal parts so natural air & moisture

do not interact with the metal to form oxide compounds.

Corrosive elements are often created through oxidation.

Care must be exercised whenever the hydraulic system is

exposed to atmosphere to minimum the introduction of

incompatible elements that may react with the fluid chemistry.

Some materials such as alloys containing magnesium, lead and

zinc are very oxidize and should be avoided in hydraulic systems.

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Rust & Corrosion Protection

Both rust & corrosion contaminate the system & increase

component wear; increase internal leakage past the affected

parts causing high temp.; and cause components to seize

through heat & closure or running clearances with debris.

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Particular care: Operate & clean

equipment to prevent the

contamination of the hydraulic

system with water or cleaning

solvents.

OxidationOxidation occurs when oxygen attacks the fluid.

Accelerated by heat, air entrainment in the fluid, metal

catalysts and the presence of water, acids, or solid

contaminants

Susceptible oil to oxidation:

Petroleum and vegetable

Operation temperature is very important:

Temps <140ºF (60ºC) , petroleum oxidizes very slow

Oxidation double for every 18ºF increased in operation

above 140ºF

Oxidation-inhibitor additives reduce oxidation of fluids.40

Inhibitor Charts

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Hydraulic Fluid Specifications

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.42


A calibrated, glass capillary

viscometer is used to

determine kinematic

viscosity.

ISO outlines 20 viscosity

grades.

Grades are based on

kinematic viscosity tests 43


The ball viscometer

can also be used to

determine kinematic

viscosity.

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Viscosity Classes

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Common industrial fluid

power systems require fluid

with viscosities in the range

of ISO grades 32, 46, or 68.

Common viscosities

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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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SAE Viscosity Classification

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Flash point is the temperature at

which the fluid vapors form a

flammable mixture with air

(temporary ignition point).

Fire point is the temperature at

which the fluid is vaporizing

rapidly enough to support

combustion (the temperature the

fluid must attain for continuous

burning).49

Flash and fire points are

important factors for many

applications.

Handling and Maintaining Hydraulic 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

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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

equipment51


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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Handling and Maintaining Hydraulic FluidsCylinder rod boots help keep dirt out of the system on

rod retraction.

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A & A Manufacturing Co., Inc., Grotite

The end.

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HYDRAULICS & PNEUMATICS Presented by: Dr. Abootorabi Hydraulic Fluids 1.

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