lecture-1.ppt
- 1. Lecture 1 Fluid power Introduction to hydraulic Vishal Chavan
- 9. Unit 1: Introduction to fluid power Objective of subject: To understand design, analysis, operation, maintenance and application of fluid power. What is fluid power Technology that deals with the generation, control and transmission of power using pressurized fluids. Used to push, pull, regulate or drive virtually all machines of modern industry eg. 1) Steers and brakes of automobile
- 10. 2) Launches spacecraft 3) Moves earth
- 11. 4) Harvest crop
- 12. 5) Mines coal 6) Machine tools
- 14. Pascal’s Law Pressure exerted at any point on a confined liquid is transmitted undiminished in all directions.
- 15. Fluid power is called hydraulics when fluid is liquid and is called pneumatics when the fluid is gas. Hydraulic systems use liquids such as petroleum oil, synthetic oil and water. The first hydraulic fluid used was water, it has many deficiencies such as freezes readily, poor lubricant and tends to rust metal components. There are two different types of fluid systems i.e. fluid transport and fluid power Fluid transport: used to transport fluid from one location to another. E.g. pumping stations, cross country gas lines, chemical processing etc.
- 16. Hydraulic Tool or equipment powered by the movement of fluid under pressure. Examples are brakes, jacks & tractor lifts.
- 17. Pneumatic Tool or equipment powered or supported by the movement of compressed air.
- 18. Pressure applied to piston “A” is transferred equally to a piston of the same size “B” because pressure is the same throughout the system. Basic principle
- 19. If the surface area of piston “B” is 10 times the surface area of piston “A”, then the force applied to piston “A” is multiplied 10 times as the force exerted on piston “B”. pressure is equal throughout the system. hydraulic advantage
- 21. Liquids provides very rigid medium for transmitting of power, operate under high pressure and provide huge forces and torques with utmost accuracy and precision. On the other hand pneumatic system exhibit spongy characteristics due to compressibility of air. It can be used in applications where low pressures can be used. Hydraulic chain saw Pneumatically controlled dextrous hand
- 22. Advantages of fluid power Power can be transmitted by three basic methods i.e. electrical, mechanical and fluid power. Most applications use combination of three methods to obtain efficienct overall system. Fluid power can transmit power economically over greater distances than mechanical types but restricted to shorter distances than electrical systems. Fluid power is versatile and manageable, it is not hindered by the geometry of machine as in case of mechanical system. Advantages: 1) Ease and accuracy of control: By the use of simple levers and push buttons, operator can start, stop, speed up and slow down and position forces with very close tolerances.
- 23. Drawbacks of fluid power Hydraulic oils are messy, leakage is impossible to eliminate completely Hydraulic lines can burst resulting in injuries to people due to high speed oil jets and flying pieces of metal if proper design is not implemented. Prolong exposure to loud noise, such as that produced by pumps can result in loss of hearing. Hydraulic oil can cause fire if leaks.
- 24. Components of a fluid power system Six basic components are required in hydraulic system 1. A Tank (Reservoir) to hold the hydraulic oil 2. A pump to force the oil through the system 3. An electric motor or other source to drive the pump 4. Valves to control oil direction, pressure and flow rate 5. An actuator to convert the pressure of the oil into mechanical force or torque to do useful work 6. Piping which carry oil from one location to other
- 25. Input / Output Force input on a hydraulic system or component results in transfer of power to output of force by the system or component.
- 26. Pump Functions in a hydraulic system by pressurizing and moving fluid from one part of the system to another.
- 27. Hydraulic pumps are usually one of four types: PISTON GEAR VANE INTERNAL ROTOR
- 28. Piston Pumps • Work well at PSI’s of 2000 or more • Single piston pump used in bottle jacks • Require several pistons working together to generate enough volume for tractor applications • Necessarily involve many moving parts
- 29. Gear Pumps • Work well at 1500 PSI and below • Work with a minimum of moving parts • Less expensive to manufacture than piston type pumps
- 30. Gear Pump driven gear idler gear
- 31. Hydraulic Motor Receives power from moving fluid to transfer hydraulic power to mechanical rotating force.
- 32. Cylinder/Actuator Piece of equipment that transfers hydraulic power into mechanical movement in one or two directions only.
- 34. Single-acting Refers to a hydraulic cylinder that works in one direction only. Double-acting Refers to a hydraulic cylinder that pushes and pulls.
- 37. Piston Internal component of a hydraulic cylinder that is moved in a linear motion by the action of fluid introduced into the cylinder.
- 38. Shaft The polished round bar that is extended from and retracted into a hydraulic cylinder.
- 39. Stroke The length of movement that a hydraulic cylinder is capable of producing.
- 40. Seal Found in hydraulic components; function is to keep fluid from leaking between moving and non- moving parts
- 41. Check Valve Restricts flow of fluid to only one direction; allows pressure to build up or be maintained.
- 42. Spool Valve Controls direction of flow of fluid in a hydraulic system to cause the different parts of the system to function.
- 45. Hydraulic power transmission • Hydraulic power transmission: Hydro = water, aulos = pipe The means of power transmission is a liquid (pneumatic gas) Hydrodynamic power transmission: • Turbo pump and turbine • Power transmission by kinetic energy of the fluid • Still the relative spatial position is fixed • Compact units Hydrostatic power transmission: • Positive displacement pump • Creates high pressure and through a transmission line and control elements this pressure drives an actuator (linear or rotational) • The relative spatial position is arbitrary but should not be very large because of losses (< 50 m) A continuously variable transmission is possible Most of this lecture will be about hydrostatic systems (in common language it is also called simply hydraulics)
- 46. Structure of a hydrostatic drive Aggregate Control elements Actuator These components and their interaction is the subject of this semester Valves, determining the path, pressure, flow rate of the working fluid Elements doing work • Linear • Rotational • Swinging Pump, motor Fluid reservoir Pressure relief valve Filter Piping
- 47. 2005/2006 I. Hydraulic and Pneumatic Systems 47 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
- 48. Advantages of hydrostatic drives Simple method to create linear movements Creation of large forces and torques, high energy density Continuously variable movement of the actuator Simple turnaround of the direction of the movement, starting possible under full load from rest Low delay, small time constant because of low inertia Simple overload protection (no damage in case of overload) Simple monitoring of load by measuring pressure Arbitrary positioning of prime mover and actuator Large power density (relatively small mass for a given power compared to electrical and mechanical drives) Robust (insensitive against environmental influences)
- 49. Disadvantages of hydrostatic drives Working fluid is necessary (leakage problems, filtering, etc.) It is not economic for large distances
- 50. Hydraulic fluid Hydraulic fluid characteristic have crucial effect on equipment performance and life. Clean, high quality fluid achieve efficient hydraulic system operation. Modern hydraulic system contain fluid with special additives to provide desired characteristics Hydraulic fluid has the following four primary functions 1. Transmit power 2. Lubricate moving parts 3. Seal clearances between mating parts 4. Dissipate heat
- 51. Hydraulic fluid Hydraulic fluid characteristic have crucial effect on equipment performance and life. Clean, high quality fluid achieve efficient hydraulic system operation. Modern hydraulic system contain fluid with special additives to provide desired characteristics Hydraulic fluid has the following four primary functions 1. Transmit power 2. Lubricate moving parts 3. Seal clearances between mating parts
- 52. Hydraulic fluid should have following properties 1. Good lubricity 2. Ideal viscosity 3. Chemical stability 4. Compatibility with system materials 5. High degree of incompressibility 6. Fire resistance 7. Good heat transfer capability 8. Low density 9. Foam resistance 10.Nontoxicity 11.Low volatility
- 53. Fluids It refers to both Gases and Liquids Liquid is a fluid that for a given mass, will have a definite volume independent of the shape of its container. Liquids are considered to be incompressible i.e. their volume does not change with pressure change. This is not exactly true, but the change in volume due to pressure changes is so small that it is ignored for most engineering applications. Gases are readily compressible, their volume will vary to fill vessel containing
- 54. Properties of fluids are density, pressure, compressibility, viscosity and viscosity index. 1. Specific weight, density and specific gravity Weight: All objects solids or fluids are pulled towards the center of the earth by the force of attraction. This force is called as weight and is proportional to the object mass, and defined by F = W = mg Specific weight: It is the ratio of weight of fluid to its volume, denoted by symbol ϒ.
- 55. 2. Force, Pressure and Head Pressure is defined as force per unit area, i.e. amount of force acting over unit area P = F/A Head: 1 meter height of water is commonly called a pressure head
- 56. Bulk modulus Mathematically it is defined by following equation
- 57. Viscosity It is single most important property of hydraulic fluid. It is measure of fluid resistance to flow, when fluid viscosity is low, the fluid flows easily and is thin in appearance. Ideal viscosity for a given hydraulic system is a compromise. Too high viscosity results in 1. High resistance to flow, sluggish operation 2. Increased power consumption due to frictional losses 3. Increased pressure drop through valves and lines 4. High temperatures caused by friction Too low viscosity results in
- 59. Kinematic viscosity Calculations in hydraulic system often involve the use of kinematic viscosity rather than absolute viscosity. It is the ratio of absolute viscosity to the density of fluid. Unit m2/s
- 60. Hydraulic fluids - tasks They have the following primary tasks: o Power transmission (pressure and motion transmission) o Signal transmission for control Secondary tasks: o Lubrication of rotating and translating components to avoid friction and wear o Heat transport, away from the location of heat generation, usually into the reservoir o Transport of particles to the filter o Protection of surfaces from chemical attack, especially corrosion
- 61. Hydraulic fluids - requirements Functional o Good lubrication characteristics o Viscosity should not depend strongly on temperature and pressure o Good heat conductivity o Low heat expansion coefficient o Large elasticity modulus Economic o Low price o Slow aging and thermal and chemical stability long life cycle
- 62. Hydraulic fluids - requirements (contd.) Safety o High flash point or in certain cases not inflammable at all o Chemically neutral (not aggressive at all against all materials it touches) o Low air dissolving capability, not inclined to foam formation Environmental friendliness o No environmental harm o No toxic effect
- 63. Hydraulic fluid types 1. Water (3%) 2. Mineral oils (75%) 3. Not inflammable fluids (9%) 4. Biologically degradable fluids (13%) 5. Electrorheological fluids (in development)
- 64. Hydraulic fluid types (contd.) - Clear water - Water with additives o Oldest fluid but nowadays there is a renaissance o Used where there is an explosion or fire danger or hygienic problem: Food and pharmaceutical industry, textile industry, mining 1. Water: Advantages: No environmental pollution No disposal effort Cheap No fire or explosion danger Available everywhere 4 times larger heat conduction coefficient than mineral oils 2 times higher compression module than mineral oils Viscosity does not depend strongly on temperature
- 65. Hydraulic fluid types (contd.) 1. Water: Disadvantages: Bad lubrication characteristics Low viscosity (problem of sealing, but has good sides: low energy losses) Corrosion danger Cavitation danger (relatively high vapour pressure) Limited temperature interval of applicability (freezing, evaporating) Consequences: needs low tolerances and very good materials (plastics, ceramics, stainless steel) components are expensive
- 66. Hydraulic fluid types (contd.) - Without additives - With additives o „Conventional” use, stationary hydraulics o Always mixtures of different oils, often with additives Additives: - decrease corrosion - increase life duration - improve temperature dependence of viscosity - improve particle transport 2. Mineral oil: Advantages: Good lubrication High viscosity (good for sealing, bad for losses) Cheap Disadvantages: Inflammable Environmental pollution
- 67. Hydraulic fluid types (contd.) - Contains water - Does not contain water o mines, airplane production, casting, rolling, where there is explosion and fire danger o Water-oil emulsions (oil synthetic) or water-free synthetic liquids 3. Non inflammable fluids: Disadvantages: Higher density, higher losses, more inclination to cavitation Limited operational temperature < 55 °C Worse lubrication characteristics, reduction of maximum load Worse de-aeration characteristics Sometimes chemically aggressive against sealing materials
- 68. Hydraulic fluid types (contd.) - Natural - Synthetic o Environmental protection, water protection o Agricultural machines o Mobile hydraulics Characteristics similar to mineral oils but much more expensive. If the trend continues its usage expands, price will drop. 4. Biologically degradable fluids: