Hydrolic Fluid purpose & properties (chapter 2)

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compressibility,Bulk modulus ,Lubrication,Sealing,Viscosity,SUS Viscosity,
SAE Viscosity Number. & ISO Viscosity Grades & comparison chart,Rust & Corrosion Protection,Pour Point,
anti-wear additives, antifoam agent, corrosion inhibitor, demulsifier, EP additive, oxidation inhibitor, pour point depressant, rust inhibitor.

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Hydrolic Fluid purpose & properties (chapter 2)

  1. 1. 10/05/13 1 Hydraulic Fluid Purpose & Properties (Chapter 2)
  2. 2. 10/05/13 2 Introduction Fluids used in mobile and stationary machinery must be effective in the transmission of power from the source to provide consistent and reliable response, safe operation, and optimum efficiency.
  3. 3. hydraulic fluids a hydraulic fluid has four primary functions: • Transmission of power • Lubrication of moving parts • Sealing of clearances between mating parts • Dissipation of heat
  4. 4. essential properties of good hydraulic fluid • Good lubricity • Ideal viscosity • Chemical and environmental stability • Large bulk modulus • Fire resistance • Good heat transfer capability • Low density • Foam resistance • Non-toxicity • Low volatility.
  5. 5. 10/05/13 5 Compressibility Ensures responsiveness of actuation or “stiffness” in a hydraulic circuit, even under high pressure. With the dynamics of loads in industrial machinery, slight decompression or compression can occur and affect actuation slightly. Petroleum-based fluids are virtually incompressible, for example. 0.4% at 1000 psi and up to 1.1% at 3000 psi operating pressure At a constant operating pressure the oil remains compressed at a given value.
  6. 6. • Bulk modulus is a measure of compressibility. Higher the bulk modulus, the less compressible or stiffer is the fluid. Where V is the original volume ΔP is the change in pressure and Δ V is the change in volume.
  7. 7. 10/05/13 7 Lubrication All hydraulic systems have components with moving parts that have the potential to come in contact with each other Components need a lubricant to prevent excess wear and the production of excess heat
  8. 8. 10/05/13 8 Sealing Internal leakage is caused by clearances inside hydraulic components, affecting the efficiency of systems Internal leakage also has the potential to create excess heat
  9. 9. 10/05/13 9 Cooling Any fluid used in hydraulic machinery absorbs and carries heat away from heat generating components such as cylinders and pumps. Some devices designed to maintain fluid quality and ensure long trouble free operation: Baffled reservoirs Coolers Strainers
  10. 10. 10/05/13 10 Fluid Properties The fluids used in hydraulic systems must posses specific desirable characteristics It is sometimes necessary to compromise some properties in favor of others that may be more important for a specific application requirement; not all fluids have all the attributes in equal strength. These properties include: Viscosity and Viscosity Index Pour Point Lubricating Ability Oxidation Additives and Inhibitors Rust and corrosion protection Demulsibility Fire resistance
  11. 11. 10/05/13 11 Viscosity Viscosity: Measure of the oil’s resistance to flow. Viscosity affects the fluid’s ability to be pumped, transmitted through the system, carry a load and maintain separation between moving surfaces.
  12. 12. 10/05/13 12 Viscosity too high (fluid is too thick) (Problems) High resistance to flow Increased energy consumption due to increased friction, increased input torque requirement at the pump High temp. created by power loss to friction Increased pressure drops due to increased resistance to flow Slow or sluggish operation/actuation Inefficient separation of air from the oil in the reservoir Pump cavitations
  13. 13. 10/05/13 13 Viscosity too low (fluid is too thin) Increased internal leakage Excess wear, seizure, particularly of pumps, could occur under heavy load because of a breakdown in lubrication film between clearances of moving parts Decreased pump effiency due to increased leakage & possible cylinder blow-by. This could cause increased cycle times or slower machine operation. Internal leakage causing an increase in operating temperatures. Most hydraulic systems run with oil (150 – 300 SUS or SSU) with the typical ISO viscosity grade (22 – 68)
  14. 14. 10/05/13 14 Viscosity Coefficient of viscosity, dynamic viscosity, absolute viscosity, or simply the viscosity of the fluid. (Same) viscosity: resistance encountered when moving one layer of liquid over another μ = τ(Δy/Δυ) μ = (N*S)/m2 or Pa*s Cgs system: use centipoise = poise/100 =0.001Pa*s Usually given
  15. 15. 10/05/13 15
  16. 16. 10/05/13 16 Kinematic Viscosity K.V. is the most common way of measuring viscosity. It is measured by the amount of time needed for a fixed volume of oil to flow through a capillary tube. ν = μ/ρ ν = m2 /s or ft2 /sec
  17. 17. 10/05/13 17 SUS Viscosity Saybolt viscosimeter: very common method in the USA. Industrial applications, hydraulic oil viscosities usually are in the vicinity of 150 SUS @ 40 C. General rule viscosity should never go below 45 or above 4000 SUS, regardless of temperature Measure how long it take liquid to flow through the orifice
  18. 18. 10/05/13 18 Viscosity Index Viscosity index is an arbitrary number that characterizes the variation of viscosity of a fluid with variations of temperature. fluid with a high viscosity index exhibits a small change in viscosity with temp. fluid with a low viscosity index exhibits a large change in viscosity with temperature
  19. 19. 10/05/13 19 Viscosity Index Indicates the extent of viscosity change for a given temperature range; should 95 or greater L = viscosity in SUS of 0-VI oil at 100°F U = viscosity in SUS of unknown-VI oil at 100°F H = viscosity in SUS of 100-VI oil at 100°F 100× − − = HL UL VI
  20. 20. 10/05/13 20 Viscosity & Temperature Hydraulic oils is directly and sometimes adversely affected by changes in temp. 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.
  21. 21. 10/05/13 21
  22. 22. 10/05/13 22 SAE Viscosity Number. & ISO Viscosity Grades & comparison chart
  23. 23. 10/05/13 23
  24. 24. 10/05/13 24 Common industrial fluid power systems require fluid with viscosities in the range of ISO grades 32, 46, or 68 or the kinematic viscosity ranges for such fluids.
  25. 25. 10/05/13 25 Rust & Corrosion Protection Corrosion is a chemical reaction between a metal and a chemical – typically an acid Extremely difficult to keep air and moisture out of hydraulic systems Both rust & corrosion contaminate the system & increase component wear. Increase internal leakage past the affected parts causing high temp. Cause components to seize through heat & closure or running clearances with debris Particular care: Operating & cleaning equipment to prevent the contamination of the hydraulic system with water or cleaning solvents
  26. 26. 10/05/13 26 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 atm. To min. 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 Should be avoided in hydraulic systems
  27. 27. 10/05/13 27 Pour Point The pour point is: lowest temperature at which an oil is observed to flow 5°F (3°C) above the temperature at which the oil in a test vessel shows no movement when the container is held horizontally for five seconds Test Method ASTM D 97 (American Society for Testing Materials)
  28. 28. 10/05/13 28 Lubricating Ability Lubricity is the ability of an oil to lubricate hydraulic components with adequate clearance to run a substantial lubrication film. Full-film lubrication and boundary lubrication
  29. 29. 10/05/13 29 Additives and Inhibitors An additive is a chemical substance added to fluid to improve certain properties. 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, EP additive, oxidation inhibitor, pour point depressant, rust inhibitor

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