Hydraulics and Pneumatics

1. Hydraulics and Pneumatics

2. Unit-1 INTRODUCTION TO HYDRAULICS AND PNEUMATICS Objectives Explain the meaning of fluid power. List the various applications of fluid power. List the advantages and disadvantages of fluid power. Explain the industrial applications of fluid power. Differentiate between mechanical ,electrical, pneumatic and hydraulics systems. Differentiate between hydraulics system and pneumatic Energy losses in hydraulic systems. ISO symbols

3. Methods for transmitting power Mechanical transmission Electrical transmission Fluid power eg:shafts, gears, chains, belts eg: wires, transformers eg: liquids or gas Fluid Power: Def: the technology that deals with the generation, control andtransmission of forces and movement of mechanical elementor system with the use of pressurized fluids - Both liquids and gases are considered as fluids

5. Advantages of a Fluid Power System: • Fluid power systems are simple, easy to operate • and can be controlled accurately • 2. Multiplication and variation of forces • 3. Multifunction control • 4. Low-speed torque • 5. Economical • 6. Low weight to power ratio • Fluid power systems can be used where safety • is of vital importance

6. Fluid power system includes – a hydraulic system (hydra in Greek meaning water) and a pneumatic system (pneuma in Greek meaning air).

7. Fluid power applications can be classified into two major segments: • Stationary hydraulics: • fixed in one position • valves are mainly solenoid operated • Applications: • Machine tools and transfer lines. • Lifting and conveying devices. • Metal-forming presses. • Plastic machinery such as injection-molding machines. • Rolling machines. • Lifts. • Food processing machinery. • Automatic handling equipment and robots. • Mobile hydraulics: • move on wheels or tracks • valves are frequently manually operated • Applications: • Automobiles, tractors , aéroplanes, missile, boats , etc. • Construction machinery. • Tippers, excavators and elevating platforms. • Lifting and conveying devices. • Agricultural machinery.

9. Types of hydraulic systems- • Hydrostatic Systems: • uses fluid pressure to transmit power • The pump used is a positive displacement pump • An example of pure hydrostatics is the transfer of force in • hydraulics. • 2. Hydrodynamic Systems: • use fluid motion to transmit power • The pump used is a non-positive displacement pump. • An example of pure hydrodynamics is the conversion of flow • energy in turbines in hydroelectric power plants.

11. A typical hydraulic system 1 – pump 2 – oil tank 3 – flow control valve 4 – pressure relief valve 5 – hydraulic cylinder 6 – directional control valve 7 – throttle valve

12. PROPERTIES OF FLUID: • Density: defined as mass per unit volume • density changes with pressure and decreases with temperature • Eg: • At 20°C, for example, the density of water changes from 998 kg/m3 at • 1 atmto 1003 kg/m3 at 100 atm, a change of just 0.5 percent. • At 1 atm, for example, the density of water changes from 998 kg/m3 • at 20°C to 975 kg/m3 at 75°C, a change of 2.3 percent,

13. Specific Weight: defined as weight per unit volume • Specific Volume : volume occupied by a unit mass of fluid

14. Specific Gravity : defined as the density of the given fluid divided by • the density of water

15. Surface tension: The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension.

16. Viscosity: • The viscosity of a fluid is a measure of its resistance to shear or angular deformation.

17. Viscosity index (VI) : • It is a relative measure of the change in the viscosity of an oil with respect to a change in temperature. • An oil having a low VI is one that exhibits a large change in viscosity with a small change in temperature. • A high VI oil does not change appreciably with a change in temperature.

18. The various properties required for an ideal hydraulic fluid are as follows: 1. Ideal viscosity. 2. Good lubrication capability. 3. Demulsibility. 4. Good chemical and environmental stability. 5. Incompressibility. 6. Fire resistance. 7. Low flammability. 8. Foam resistance. 9. Good heat dissipation. 10. Low density. 11. System compatibility.

19. Lubrication Capability: • Hydraulic fluids must have good lubricity to prevent friction and • wear between the closely fitted working parts such as vanes of pumps, • valve spools, piston rings and bearings.

20. Demulsibility • The ability of a hydraulic fluid to separate rapidly from moisture and successfully resist emulsification is known as “demulsibility.” • If an oil emulsifies with water, the emulsion promotes the destruction of lubricating and sealant properties. • Highly refined oils are basically water resistant by nature. • Good Chemical and Environmental Stability (Oxidation and Corrosion Resistance) : • Most fluids are vulnerable to oxidation, as they come in contact with oxygen in air. • Mineral oils or petroleum-based oils (widely used in hydraulic systems) contain carbon and hydrogen molecules, which easily react with oxygen. • The oxidation products are highly soluble in oil and being acidic in nature they can easily corrode metallic parts

21. Neutralization Numbers : • is a measure of the acidity or alkalinity of hydraulic oil. • This is referred to as the pH value of the oil. High acidity causes the oxidation rate in oil to increase rapidly. • Incompressibility: • hydraulic fluids as incompressible, in practice, they are relatively • compressible. • Most mineral oils undergo reduction in the volume of • about 0.7% for every 100 bar rise in pressure. • the compressibility of a fluid is greatly influenced by temperature • and pressure.

22. Types of Hydraulic Fluids : Petroleum-based fluid Emulsions Water glycol Synthetic fluids Vegetable oils Biodegradable hydraulic fluids

23. Petroleum-based fluid: Mineral oils are the petroleum-based oils Advantage: they are easily available and are economical they offer the best lubrication ability , least corrosion problems and are compatible with most seal materials Disadvantage: Flammability: They pose fire hazards, mainly from the leakages, in high-temperature environments such as steel industries, etc.

24. 2.Emulsions: • a mixture of two fluids that do not chemically react with others • Emulsions of petroleum-based oil and water are commonly used. • An emulsifier is normally added to the emulsion, which keeps liquid as small droplets and remains suspended in the other liquid. • Two types of emulsions are in use: • a).Oil-in-water emulsions: • water as the main phase, while small droplets of oil are dispersed in it • the oil dilution is limited, about 5%; hence, it exhibits the characteristics of water. • Limitations: poor viscosity, leading to leakage problems, loss in volumetric efficiency and poor lubrication properties. • These problems can be overcome to a greater extent by using certain additives. Such emulsions are used in high-displacement, low-speed pumps (such as in mining applications).

25. b) Water-in-oil emulsions/inverse emulsions: • basically oil based in which small droplets of water are dispersed throughout the oil phase. • The commonly used emulsion has a dilution of 60% oil and 40% water • popular fire-resistant hydraulic fluids • exhibit more of an oil-like characteristic; hence, they have good viscosity and lubrication properties. • These emulsions are good for operations at 25°C, as at a higher temperature, water evaporates and leads to the loss of fire-resistant properties.

26. 3. Water glycol: • nonflammable fluid commonly used in aircraft hydraulic systems. • has a low lubrication ability as compared to mineral oils and • is not suitable for high-temperature applications. • It has water and glycol in the ratio of 1:1. • Because of its aqueous nature and presence of air, it is prone to • oxidation and related problems. • It needs to be added with oxidation inhibitors. • Enough care is essential in using this fluid as it is toxic and corrosive • toward certain metals such as zinc, magnesium and aluminum.

27. 4. Synthetic fluids: • based on phosphate ester, is another popular fire-resistant fluid. • It is suitable for high-temperature applications, since it exhibits good viscosity and lubrication characteristics. • It is not suitable for low-temperature applications. • It is not compatible with common sealing materials such as nitrile. • 5. Vegetable oils: • biodegradable and are environmental safe. • They have good lubrication properties, moderate viscosity and are less expensive good fire resistance characteristics with certain additives, • tendency to easily oxidize and absorb moisture. • The acidity, sludge formation and corrosion problems are more severe • in vegetable oils than in mineral oils. • Hence, vegetable oils need good inhibitors to minimize oxidation problems

28. 6. Biodegradable hydraulic fluids / bio-based hydraulic fluids : • Bio-based hydraulic fluids use sunflower, soybean, etc., • as the base oil and hence cause less pollution in the case of • oil leaks or hydraulic hose failures. • These fluids carry similar properties as that of a mineral • oil–based anti-wear hydraulic fluid,

29. Factors Influencing the Selection of a Fluid: 1. Operating pressure of the system. 2. Operating temperature of the system and its variation. 3. Material of the system and its compatibility with oil used. 4. Speed of operation. 5. Availability of replacement fluid. 6. Cost of transmission lines. 7. Contamination possibilities. 8. Environmental condition (fire proneness, extreme atmosphere like in mining, etc.). 9. Lubricity. 10. Safety to operator. 11. Expected service life.

30. Hydraulic fluids - tasks • They have the following primary tasks: • Power transmission (pressure and motion transmission) • Signal transmission for control • Secondary tasks: • Lubrication of rotating and translating components to avoid friction and wear • Heat transport, away from the location of heat generation, usually into the reservoir • Transport of particles to the filter • Protection of surfaces from chemical attack, especially corrosion

31. Hydraulic fluids - requirements • Functional • Good lubrication characteristics • Viscosity should not depend strongly on temperature and pressure • Good heat conductivity • Low heat expansion coefficient • Large elasticity modulus • Economic • Low price • Slow aging and thermal and chemical stability  long life cycle

32. Hydraulic fluids - requirements (contd.) • Safety • High flash point or in certain cases not inflammable at all • Chemically neutral (not aggressive at all against all materials it touches) • Low air dissolving capability, not inclined to foam formation • Environmental friendliness • No environmental harm • No toxic effect

33. Ideal and real fluid

34. Laminar flow/streamline • In streamline flow, the fluid appears to move by sliding of laminations of infinitesimal thickness relative to adjacent layers; that is, the particles move in definite and observable paths or streamlines.

35. 2.Turbulent flow: It is characterized by a fluid flowing in random way. The movement of particles fluctuates up and down in a direction perpendicular as well as parallel to the mean flow direction.

37. Reynolds Number • If Re is less than 2000, the flow is laminar. • If Re is greater than 4000, the flow is turbulent. • Reynolds number between 2000 and 4000 covers a critical zone between laminar and turbulent flow.

38. c) Transmission of power b) Pascals’s law a) Hydrostatic pressure e) Continuity g) Bernoulli equation d) Transmission of pressure f) Flow resistance Governing laws

39. Distribution of fluid power: • Steel Pipes: • extensively used in fluid power systems, although they are rapidly being supplemented by steel or plastic tubing. • disadvantages of steel pipes are their weight and the large number of fitting requirement for connection . • advantage is its mechanical strength and particularly its ability to withstand abuse.

40. Screwed Connections : Steel piping in fluid power systems is most often joined by threaded connections. • Steel Tubing : • widely used material for hydraulic system conductors. • it can be easily formed to fit irregular paths so that fewer • fittings are required. • lessened chance of leakage since every connection is a • potential leak point. • It is also relatively small and light, thus making it easy to use.

41. Compression Joints : • comprise a loose ring having a cone-shaped nose that must face the open end of a tube, a mating tapered barrel and a retaining nut. • The end of the tube must always be cut square and deburred before assembly. • When the tube is pushed fully in the fitting and the retaining nut is tightened, the compressive action forces the nose of the ring into the surface of the metal tube, • creating a permanent and very strong • interference fit that is capable of withstanding • pressure in excess of 350 bar.

42. Plastic Conductors: • available in polyethylene, polypropylene, polyvinyl chloride and nylon • compatible with most hydraulic fluids, however, and could safely be used in low-pressure applications. • Flexible Hoses : • A hose is manufactured from natural and synthetic rubbers and several plastics. • This material is supported by fabric or by wire cloth, and wire braid may be used between plies or as an outside casing for high-pressure applications

43. Quick Disconnect Couplings : • This type of coupling in conjunction with flexible hoses connects movable components together hydraulically. • Typical applications are mobile trailers and agriculture machinery towed behind tractors. • usually comprise a plug and socket arrangement that provides a leak-proof joint when two parts are connected together, and that can be released easily without the use of tools • Each half of the coupling contains a spring-loaded ball or poppet that automatically closes on disconnection, so that two completely leak-free joints are obtained. • Leaking during the process of disconnecting or connecting coupling is negligible

44. Types of Quick Couplings: There are three basic types of quick couplings; single shut-off, double shut-off, and straight-through

45. Single shut-off couplings/One-Way shut-off or Pneumatic couplings: • installed with the valved half on the pressure side of the circuit to provide automatic shut-off flow when the coupling is disconnected. • low working pressure capabilities ranging from 100 to 300 PSI. • The are commonly made from brass or steel. • Applications -lubrication, paint spray, and carpet cleaning equipment.

46. Double Shut-off Couplings /Two-way shut-off / Hydraulic Couplings:

47. 3. Straight-through coupling:

48. BENDS:

49. ENERGY LOSSES IN HYDRAULIC SYSTEMS: Darcy–Weisbach Equation : Head losses in a long pipe in which the velocity distribution has become fully established or uniform along its length can be found by Darcy’s equation as Where, f is the Darcy friction factor, L is the length of pipe (m), D is the inside diameter of the pipe (m), v is the average velocity (m/s) and g is the acceleration of gravity (m/s2).

50. Frictional Losses in Laminar Flow: Darcy’s equation can be used to find head losses in pipes experiencing laminar flow by noting that for laminar flow, the friction factor equals the constant 64 divided by the Reynolds number: Substituting this into Darcy’s equation gives the Hagen–Poiseuille equation: