Hydraulic Fluids

1
Fluid Power

• Chapter 3
• Hydraulic Fluids

2
Fluid Requirements

• Transmit power
• Lubricate moving parts
• Seal clearances
• Heat dissipation

3
Fluids

• Additives are put in the fluid at the refinery to
  improve different properties of the fluid.
• All fluids are basically non-compressible but all
  fluids are not good for hydraulic systems.

4
Power Transmission

• Hydraulic fluids must be non-compressible.
• Hydraulic fluids must flow easily through the
  system components.
• Too much resistance to flow results in power loss
  and inefficiency.

5
Lubrication

• In most hydraulic components,internal lubrication
  is provided by the fluid.
• Wearing parts slide by each other on a film of
  fluid.
• Anti-wear additives ensure longer system life.
• Rust prevention additives may be used.

6
Lubrication
7
Sealing

• In many components, the only sealing is provided
  by a film of fluid.
• Close mechanical fits and fluid viscosity
  determine the leakage rate.
• Internal leakage.

8
Heat Dissipation

• Cooling of the system is aided by the circulation
  of the hydraulic fluid through the systems lines
  and reservoir.
• Other methods will be discussed later.

9
Cooling
10
Quality requirements

• Prevention of sludge, gum,rust varnish
• Anti-foaming agents
• Stability of fluid
• Anti-corrosion anti-pitting
• Separation of water
• Temperature range
• Compatibility

11
Compatibility

• Compatibility is probably the most overlooked
  maintenance problem in a fluid power system.
• Seals, hoses, components and other fluids.

12
Fluid properties

• Viscosity
• Pour point
• Lubrication ability
• Oxidation resistance
• Rust corrosion protection
• Demulsibility

13
Viscosity

• The measure of a fluids resistance to flow.
• Different testing methods are used.
• Low viscosity fluids flow easily.
• High viscosity fluids flow slower.

14
High viscosity fluids

• High viscosity fluids seal better but
• creates higher friction
• uses more power
• results in slower operations
• increases pressure drops
• keeps air entrained in the fluid

15
Low viscosity fluids

• have more internal leakage
• creates more system wear because the fluid breaks
  down quicker
• lowers pump efficiency
• slow the systems operations
• increase the chance of external leakage

16
Viscosity temperature

• Temperature affects the viscosity.
• High temps tend to thin the fluid and low temps
  tend to thicken the fluid.
• VI numbers indicate how much the temperature
  affects the fluids viscosity.
• Higher numbers indicate a more stable fluid and
  lower numbers indicates a fluid that will change
  more radically with changes in temperature.

17
Pour point

• The lowest temperature at which the fluid will
  flow.
• You should specify a fluid with a pour point
  rating at least 20 degrees colder than the
  anticipated low temperature.

18
Lubricating ability

• Full film lube--the most desirable form creates
  a substantial film of fluid between the wearing
  parts. There is no metal to metal contact.
• In speed or high pressure applications the full
  film lubrication can become squeezed very thin.
  This is called boundary lubrication. There may
  be some metal to metal contact.

19
Full film lubrication
20
Boundary lubrication
21
Oxidation

• Oxidation is a chemical union with oxygen.
• Reduces fluid life.
• In petroleum based fluids carbon hydrogen
  combine with oxygen which creates --------????
• Can cause gums acids to form in the fluid which
  can plug clearances and orifices.

22
Catalysts

• There are always catalysts present in a hydraulic
  system. These catalysts will accelerate the
  problem of oxidation.
• heat
• pressure
• contaminants including water
• metals
• agitation

23
Heat

• Oxidation will double for every 18 degrees above
  135 degrees F.
• 135 degrees is a good temperature to operate a
  system.
• At 153 oxidation doubles, 171 it doubles again
  and again at 189 degrees.
• Increases acid formation in the fluid

24
Acid corrosion
25
Additives

• Some additives will react chemically with the
  fluid to lessen oxidation.
• Rust corrosion preventers
• Demulsifiers separate water out of the fluid
• Additives have to be compatible

26
Petroleum based fluids

• are the most widely used
• factors affecting characteristics
• type of crude
• refining methods
• additives
• have excellent lubrication properties
• naturally protects against rust,

27
Petroleum based fluids

• Seal well
• will easily dissipate heat
• are easy to keep clean
• accept additives
• are not fire resistance.

28
Fire resistant fluids

• Are not fire proof!
• 4 major types
• are not, generally, compatible with other fluids
  and some seals

29
Fluid maintenance

• Keep system clean use filters strainers, close
  tank lids and fillers
• store oil drums on their sides under a roof if
  possible
• use clean containers, hoses, pumps for
  transferring new fluids
• do regular oil analysis
• follow manufacturers guidelines

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