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

2. Task for hydraulic fluids

3. 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.

4. 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.

5. 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

6. 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

7. 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 (ν).

8. 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.

9. Viscosity – temperature diagram

10. Viscosity – pressure characteristics
At approx. 350 to 400 bar the viscosity is generally already double that at 0 bar.

11. 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.

12. 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.

13. Performance Characteristics of a Hydraulic Fluid
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.

14. Performance Characteristics of a Hydraulic Fluid
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.

15. 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

16. Performance Characteristics of a Hydraulic Fluid
A well-designed reservoir helps maintain proper fluid temperature.

17. 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

18. 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.

19. 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

20. 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

21. 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

22. Types of hydraulic fluid
1. Hydraulic oils (divided into 3 classes according to DIN and 51525) HL
HLP HV
2. Hydraulic fluids with low inflammability
Example:

23. 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.

24. 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.

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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.

33. Selection of fluids
The 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

34. 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 .

35. 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)

36. 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

37. 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

38. 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.

39. 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.

40. 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 <140ºF (60ºC) , petroleum oxidizes very slow
Oxidation double for every 18ºF increased in operation above 140ºF
Oxidation-inhibitor additives reduce oxidation of fluids.

41. Inhibitor Charts

42. 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.

43. 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

44. Hydraulic Fluid Specifications
The ball viscometer can also be used to determine kinematic viscosity.

45. Viscosity Classes

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

47. 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

48. SAE Viscosity Classification

49. 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.

50. 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

51. 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

52. 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

53. Handling and Maintaining Hydraulic Fluids
Cylinder rod boots help keep dirt out of the system on rod retraction.
A & A Manufacturing Co., Inc., Grotite

54. The end.