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Basic hydraulics


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Hydraulics today has become a way of life as most applications have some form of system ingrained. This paper is an endevor to present the very basics of hydraulics and overcome its basic fear.

Published in: Business
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Basic hydraulics

  2. 2. A TALK OVERVIEW • • This talk has been designed to provide instruction on the concept and operation of the basic components of the hydraulic system. It also describes the various components of a typical hydraulic system, their construction and functions, and their relationship to each other. However to really appreciate & know about hydraulics ‘hands on’ experience, is a MUST.
  3. 3. Fluid Power System • Fluid Power Systems are power transmitting assemblies employing pressurised liquid or gas to transmit energy. • Fluid power can be divided into two basic disciplines > Hydraulics – Employing pressurised liquid > Pneumatics - Employing Compressed gas
  4. 4. What is Hydraulics? • Hydraulics is derived from the Greek word - Hydor meaning Water - Aulos meaning Pipe
  5. 5. Definition of Hydraulics In simple language: Confined liquids under pressure made to do work. OR Science of transmitting force / motion through medium of confined liquid
  6. 6. HYDRAULICS DEFINED FURTHER… • Fluid Mechanics is the physical science and technology of the static and dynamic behavior of fluids. Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties.
  7. 7. PASCAL’S LAW Pascal Law – which is the basis for all hydraulic systems, is named after the French Scientist – Blaise Pascal, who established the law.
  8. 8. Do you remember Pascal’s Law? • • It states that “ Pressure exerted anywhere in a confined fluid is transmitted equally in all directions throughout the fluid. The basic idea behind all hydraulic system is based upon that principle & can be simply stated as: Force applied at one point is transmitted to another point using an incompressible fluid.
  10. 10. Working Principle of a Hydraulic Press
  11. 11. Functions of Hydraulic Oil • It transmits power. • It lubricates moving parts • It seals clearances between moving parts • It dissipates heat
  12. 12. Advantages of oil in Hydraulics • Variable speed • Reversible • • • • • • • • • • need direction. Over load protection overSmall package : power Can be stalled : Simple design Self lubricated Flexible location components. Smooth Acts as coolant Acts as seal mating parts. Noise free : : : : Possible to control speed through valve. : Instant reverse motion is possible. No to stop the system to change : Protected through relief valve from loading. Components are smaller than other transmitting system. Not possible on direct drive system from Electric motor / Diesel engine. Pre-engineered components available. Hydraulic oil lubricates the parts. Flexible hoses virtually eliminate the problem of the hydraulic : Incompressible, no vibration. : It dissipates heat / cools the component, ; It seals clearances between two : No noise.
  13. 13. Force that is applied at one point is transmitted to another point using an incompressible fluid • In this drawing, two pistons (green) fit into two glass cylinders filled with oil (blue) and connected to one another with an oil-filled pipe. If you apply a downward force to one piston (the left one in this drawing), then the force is transmitted to the second piston through the oil in the pipe
  14. 14. • Force the left is 2 inches in diameter (1-inch radius), Multiplication Assume that the piston on while the piston on the right is 6 inches in diameter (3-inch radius). The area of the two pistons is Pi * r2 . The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is 9 times larger than the piston on the left. What that means is that any force applied to the left-hand piston will appear 9 times greater on the right-hand piston. So if you apply a 100-pound downward force to the left piston, a 900pound upward force will appear on the right
  15. 15. Hydraulic System • Reservoir • Filter • Hydraulic Pump • Directional Control Valve • Pressure Control Valve
  16. 16. Reservoir- Properties First a tank is needed to store the hydraulic oil Tank / Reservoir Storing oil Compensates difference in volume when actuators are used It dissipates heat It allows foreign particles to settle down Baffle separates inlet line with the return line and allows the air bubbles to escape
  17. 17. More Properties of Reservoirs • It allows condensed water to settle at the bottom of the tank • Breather on the top of the tank allows to maintain atmospheric pressure and avoid creation of vacuum • Sight glass will indicate the level of the oil. Mercury bulb indicates the oil temperature • Oil filling inlet will have a filter for avoiding contamination.
  18. 18. PUMPS • Hydraulic Pump is the most important component in the hydraulic system. • Function of the Hydraulic Pump is to convert Mechanical Energy to Hydraulic Energy • Hydraulic Pump are classified in two categories: - Hydro-dynamic - Hydro-static
  19. 19. Pump Now we need a pump to create flow Tank Pump Two types of hydraulic pumps are most commonly used: - Rotary Pumps - Reciprocating Pumps
  20. 20. ROTARY & RECIPROCATING TYPES • Common Pumps in Rotary type are: - Gear Pumps - Vane Pumps • Common Pumps in Reciprocating type • are: Axial Piston Pump Radial Piston Pump
  21. 21. ACTUATORS • An actuator is a mechanical device for moving or controlling a mechanism or system. An actuator typically is a mechanical device that takes energy & converts it to a desirable form for usage or application. Actuator Tank Pump
  22. 22. ACTUATORS Contd… • There are mainly two types of Actuators: - Linear actuators (single acting cylinders, double acting cylinders) - Rotary actuators (vane motors, gear motors, piston motors etc.)
  23. 23. Types of Valves • There are three main types of Valves: - Pressure Control Valves (relief valves, pressure regulating valve, pressure reducing valve etc.) - Directional Control Valves (check valve, axial spool valve, ball valve etc.) - Flow Control Valves (needle valve, throttle check valve etc.)
  24. 24. Hydraulic System – some applications of the basic components Actuator Hoses to connect the components Piston reverse movement is not possible We need a direction control valve to change the direction of flow as per requirement Pump Tank
  25. 25. Hydraulic System Actuator There are mainly two design principles for valves Direction Control Valve - Spool valves - Poppet valves Pump Tank
  26. 26. Hydraulic System Actuator Direction Control Valve The control valve is at neutral position Pump Tank
  27. 27. Hydraulic System Actuator Now the control valve is shifted to left Direction Control Valve Pump Tank
  28. 28. Hydraulic System Actuator Direction Control Valve To change the piston movement in opposite direction the control valve is now shifted to right Pump Tank
  29. 29. Hydraulic System Actuator Is it a complete circuit ? OR We need some thing more Direction Control Valve Pump Tank
  30. 30. Hydraulic System Actuator Piston at end -No room to move Pressure increases Direction Control Valve yes We need some thing more Pump Tank We need to control the system pressure
  31. 31. Hydraulic System Actuator Direction Control Valve Pressure relief valve Pump Tank
  32. 32. Hydraulic System Actuator Direction Control Valve Pressure relief valve Pump Tank
  33. 33. Hydraulic System Actuator Direction Control Valve Pressure relief valve Stops pressure increasing beyond the preset value Pump Tank
  34. 34. Hydraulic System Actuator Now we have a system which can work But is this system protected from dirt ? Direction Control Valve Pressure relief valve Pump Tank
  35. 35. Hydraulic System Actuator We need to protect the system from dirt by installing a FILTER in the system Direction Control Valve Pressure relief valve We have a system now which can work safely Pump Filter Tank
  36. 36. FILTERS • There are basically three types of Filters - Suction line filters - Pressure line filters - Return line filters
  37. 37. Why is filtration necessary? • Impurities in the Hydraulic • system affect the components of the hydraulic system and shorten their service life. Reduction in service life of the components occurs in two ways: - Wear and Tear - Breakdown of component Filters are used to remove the smallest insoluble particles and keep the hydraulic system clean
  38. 38. Hydraulic System Now we know : Actuator • • Pump creates flow • Resistance creates pressure • Actuators perform the work • Hoses transmit the oil • D.C. Valves change direction of oil flow • Pressure relief valve Filter cleans the system • Direction Control Valve A Reservoir contains oil Relief valves control the maximum system pressure. Pump Filter Tank
  39. 39. Hydraulic System Actuator Few more facts: • • Direction Control Valve Pressure relief valve Pump Filter Tank Pressure increases the system capacity Flow increases the system speed
  40. 40. This Excavator weighs over 28 tons, but has swift movements. The bucket can effortlessly scoop out more than a cubic meter of rock weighing about 2.0T
  41. 41. Transmission of Hydraulic Power is connected to a pair of pumps that can • The engine generate 140 gallons per minute at 4,500 psi. You can see from the picture that the arm has a pair of pistons working in unison at the "shoulder" -- one at the "elbow" and then one to rotate the bucket.
  42. 42. Transmission of Hydraulic Power • These pistons, along with the two track motors and the rotating motor, are all controlled by two joy sticks and four pedals in the cab. These controls send electrical signals to an electrically-operated valve block located next to the pump.
  43. 43. Transmission of Hydraulic Power • From the valve block, high-pressure hydraulic lines make their way to the cylinders & they get activated whereby the bucket can be moved as desired from the cabin with the touch of a button.
  44. 44. Some Basic Calculations • A 4-inch piston has an area of 12.56 square inches. If the pump generates a • maximum pressure of 3,000 pounds per square inch (psi), the total pressure available is 37,680 pounds, or about 20 tons. Another thing you can determine is the cycle time of the piston. To move a 4-inch-diameter piston 24 inches, you need 3.14 * 22 * 24 = 301 cubic inches of oil. A gallon of oil is about 231 cubic inches, so you have to pump almost 1.5 gallons of oil to move the piston 24 inches in one direction. These form the basic criteria while selecting the hydraulic pump. For example the actual engine, pump & sump details for this excavator is: Engine Cummins 6CT 8.3-C 8,270 cubic centimeters 340 horsepower at 1,900 rpm Pump Maximum pressure: 5,000 psi (4,500 psi) Oil flow: 2x270 liters per minute Capacities Fuel: 530 liters Engine oil: 22 liters Hydraulic oil: 320 liters
  46. 46. What exactly is "full hydraulic steering?" • The expression refers to any steering system configurations where a vehicle is steered solely by means of a hydraulic circuit comprising, as a minimum, a pump, lines, fluid, valve, and cylinder (actuator). that is to say, the vehicle is steered (usually via the front wheels) purely by a hydraulically powered steering cylinder. This is an important distinction from "hydraulically assisted" steering, where hydraulic power serves only to assist a mechanical steering system (as is the case with the hydraulically assisted power steering on virtually every light car / truck on the road today). It indicates that the vehicle is steered ONLY by hydraulics, with no other system (mechanical linkage) in place.
  47. 47. Why use hydrostatic steering? • Because there are a number of distinct advantages : • Power - depending on system design parameters (flow, pressure, cylinder size, etc.) hydro steering can develop steering force FAR in excess of any other mechanical, electrical, or hydraulically boosted system. This is a must for massive construction equipment. It is also extremely advantageous to 4x4s with big tires, locker differentials, low tire pressures, the must negotiate and be steered in extremely challenging terrain. For a given amount of steering input effort, no other system can match the power output of a hydro steering system. Flexibility - the very nature of fluid power (hydraulics) allows for great flexibility in system design and mounting. The steering need not be constrained by the requirements for mechanical linkages. Operator comfort - because of the power generated, required operator input levels are very low in hydro steering systems. Control - depending on system design and tuning, precise, custom steering can be arranged, (for example, a system with very few turns of the steering wheel from lock to lock) Weight - the power to weight ratio of hydrostatic systems generally far outstrips traditional hydraulically boosted mechanically actuated steering systems. Smoothness - hydro steering systems are smooth and quiet in operation. Vibration is kept to a minimum. kickback, bump steer, and operator fatigue are all but eliminated. Overload protection - when properly designed, automatic valves can guard the system against a breakdown from overloading • • • • • •
  48. 48. The component in the top right of the picture is the hydraulic steering directional control valve / metering section; and is the heart of the system
  49. 49. Basic wrap-up & Re cap of the system so far…. • Reservoir - this is the hydraulic fluid (or power • steering fluid) reservoir that stores the fluid necessary for the system. Supply pump - this is the power steering pump, note that in many automotive applications the pump and reservoir are integrated into one unit
  50. 50. How it works (tracing the circuit). • The reservoir supplies fluid to the pump. The pump pumps the fluid • to the steering unit. When the operator turns the steering wheel, connected to the steering unit via the steering shaft, the steering unit directs pressurized fluid to and from the cylinder. In response the cylinder extends or retracts. The cylinder is connected to the steered wheels and therefore the wheels steer. Fluid then returns to the reservoir from the steering unit via the filter.
  51. 51. Relief valve • - This is simply a pressure relief valve. If a malfunction in the system causes the pressure to rise too high, the relief valve opens and the fluid simply passes back to the reservoir. In virtually all automotive power steering pumps, the relief valve is built into the pump
  52. 52. Hydraulic Symbols Definitions of LINES continuous line - flow line dashed line - pilot, drain envelope - long and short dashes around two or more component symbols
  53. 53. Advanced Hydraulic Symbols
  54. 54. Hydraulic Symbols
  55. 55. Hydraulic & Pneumatic Symbols • Some basic symbols:
  56. 56. Some Hydraulic & Pneumatic Symbols
  57. 57. Some more Hydraulic Symbols
  58. 58. Hydraulic Pumps & Motors Symbols • More Symbols
  59. 59. Hydraulic Pumps • Any hydraulic pump performs two functions. First, its • mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump. Second, its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system. Shown below is a Variable-displacement, pressurecompensated vane pump
  60. 60. Classification of pumps • All pumps may be classified as either positive• • displacement or non-positive-displacement. Most pumps used in hydraulic systems are positive-displacement. A non-positive-displacement pump produces a continuous flow. However, because it does not provide a positive internal seal against slippage, its output varies considerably as pressure varies. Centrifugal and propeller pumps are examples of non-positivedisplacement pumps. In a positive-displacement pump , slippage is negligible compared to the pump's volumetric output flow. If the output port were plugged, pressure would increase instantaneously to the point that the pump's pumping element or its case would fail or the pump's prime mover would stall.
  61. 61. Positive-displacement principle • A positive-displacement pump is one that displaces (delivers) the same amount of liquid for each rotating cycle of the pumping element. Constant delivery during each cycle is possible because of the close-tolerance fit between the pumping element and the pump case
  62. 62. FAULT TRACING OF HYDRAULIC SYSTEMS • So in conclusion I may say that to a beginner an hydraulic system or circuit may look complicated & fault tracing difficult. • But if one follows the root cause approach & checks the system from the basic parameters then fault tracing is actually easy. • However some tools like clip on flow & pressure gauges, temperature gauges etc are required.