DRIVE SYSTEM ENT 271

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HYDRAULICS PNEUMATICS

• Hydraulic Fluids

Presented by Dr. Abootorabi
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Task for hydraulic fluids
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Performance Characteristics of a Hydraulic Fluid

• When selecting a fluid, consider its

• 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

The most important distinguishing feature of
hydraulic fluids is viscosity.
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Performance Characteristics of a Hydraulic Fluid

• 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.

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Performance Characteristics of a Hydraulic Fluid

• Viscosity is the internal resistance to flow of a
  liquid (resistance to flow).

• 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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Viscosity

• Viscosity may be the most important property of a
  hydraulic fluid.
• If the viscosity is too high, it may results in
• High resistance to flow, causing sluggish
  operation
• Increased power consumption due to frictional
  losses
• Increased pressure drop through valves and lines
• High temperature due to friction

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Viscosity

• On the other hand, if the viscosity is too low,
  it may result in
• Increased oil leakage past seals
• Excessive wear due to breakdown of the oil film
  between mating parts
• There are two kinds of viscosity Absolute
  viscosity (µ) and kinematic viscosity (?).

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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.

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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 Index

• 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.

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Performance Characteristics of a Hydraulic Fluid

• 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

Pour point is important in cold weather.
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Performance Characteristics of a Hydraulic Fluid

• Pour point is 3C 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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Performance Characteristics of a Hydraulic Fluid

• Normal operating temperature range for hydraulic
  fluid in the reservoir is typically 110F to
  140F (43C to 60C) .
• Operating the system in this temperature range
  will result in an acceptable fluid service life.

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Performance Characteristics of a Hydraulic Fluid

• 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

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Performance Characteristics of a Hydraulic Fluid

• A well-designed reservoir helps maintain proper
  fluid temperature.

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Performance Characteristics of a Hydraulic Fluid

• Demulsibility 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
  chemistry

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Performance Characteristics of a Hydraulic Fluid

• 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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Performance Characteristics of a Hydraulic Fluid

• 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 Fluid

• 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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Fire Resistance

• Fluid 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 removed

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Types of hydraulic fluid

• 1. Hydraulic oils (divided into 3 classes
  according to DIN 51524 and 51525)
• HL
• HLP
• HV
• 2. Hydraulic fluids with low inflammability

Example
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Types of hydraulic fluid

• 1. Hydraulic oils

Most common hydraulic fluid in use consists of
petroleum base blended with additives to produce
the desired operating properties.
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Types of hydraulic fluid
2. Hydraulic fluids with low inflammability

• 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.

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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

• Applications
• Steel works and rolling mills
• Automotive manufacture
• Offshore industry
• On aircraft and ships

• Hard coal mining
• Die-casting machines
• Control units for power station turbines

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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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Hydraulic fluids with low flammability

• 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)

• 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

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Hydraulic fluids with low flammability

• 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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Hydraulic fluids with low flammability

• All synthetic fluids provide excellent fire
  resistance. These are not water based.
• Phosphate ethers are the most common synthetic
  hydraulic fluids.

• All synthetic fluids meet the basic requirements
  of a hydraulic fluid
• Appropriate viscosity
• Good high-pressure performance
• Good lubrication

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Hydraulic fluids with low flammability

• 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 systems

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Another type of hydraulic fluids

• Biodegradable 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

Biodegradable fluids are important when reducing
environmental impact.
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Selection of fluids

• The fluid supplier must understand the nature of
  the fluid application
• Environment
• Types of components and their manufactures
  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.

• 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 .

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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 gt3000 psi (or 200
  bar)

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Hydraulic Fluid Additives

• Demulsifier additives increase the fluids
  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

• Its 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

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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.

Particular care Operate clean equipment to
prevent the contamination of the hydraulic system
with water or cleaning solvents.
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Oxidation

• Oxidation 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 lt140ºF (60ºC) , petroleum oxidizes very
  slow
• Oxidation double for every 18ºF increased in
  operation above 140ºF
• Oxidation-inhibitor additives reduce oxidation of
  fluids.

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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.

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Hydraulic Fluid Specifications

• A calibrated, glass capillary viscometer is used
  to determine kinematic viscosity.
• ISO outlines 20 viscosity grades.
• Grades are based on kinematic viscosity tests

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Hydraulic Fluid Specifications

• The ball viscometer can also be used to determine
  kinematic viscosity.

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Viscosity Classes
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Common viscosities
Common industrial fluid power systems require
fluid with viscosities in the range of ISO grades
32, 46, or 68.
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Hydraulic Fluid Specifications

• 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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Hydraulic Fluid Specifications

• 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).

Flash and fire points are important factors for
many applications.
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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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Handling and Maintaining Hydraulic Fluids

• 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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Handling and Maintaining Hydraulic Fluids

• 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 Fluids

• Cylinder rod boots help keep dirt out of the
  system on rod retraction.

A A Manufacturing Co., Inc., Grotite
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• The end.