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HYDRAULICS & PNEUMATICS

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HYDRAULICS & PNEUMATICS

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  1. HYDRAULICS & PNEUMATICS • Actuators Presented by: Dr. Abootorabi

  2. Hydraulic Cylinders • Actuators are the components used in a hydraulic system to provide power to a required work location. • Cylinders are the hydraulic system components that convert fluid pressure and flow into linear mechanical force and movement.

  3. Hydraulic Cylinders • A basic cylinder consists of: • Piston • Piston rod • Barrel • The piston forms sealed, variable-volume chambers in the cylinder. • System fluid forced into the chambers, drives the piston and rod assembly.

  4. Hydraulic Cylinders • Seals prevent leakage between: • Piston and cylinder barrel • Piston rod and head • Barrel and its end pieces • Wiper seal, or scraper, prevents dirt and water from entering the cylinder during rod retraction.

  5. Hydraulic Cylinders • Various seals are used in a cylinder

  6. Hydraulic Cylinders • Various seals are used in a cylinder

  7. Hydraulic Cylinders • Various seals are used in a cylinder

  8. Hydraulic Cylinders • Cylinders are typically classified by operating principle: • Single-acting • Double-acting Single-acting Double-acting

  9. Hydraulic Cylinders • Single-acting cylinder exert force either on extension or retraction: • They require an outside force to complete the second motion (either by a spring or by the weight load). • Double-acting cylinder generate force during both extension and retraction: • Directional control valve alternately directs fluid to opposite sides of the piston • Force output varies between extension and retraction

  10. Hydraulic Cylinders • Single-acting cylinder • hydraulic ram (or plunger cylinder): piston and rod form one unit

  11. Hydraulic Cylinders • Single-acting cylinder Scissor lifting table:

  12. Hydraulic Cylinders • Double-acting cylinder

  13. Hydraulic Cylinders • Double-acting cylinder types:

  14. Hydraulic Cylinders • Double-acting cylinder types:

  15. Hydraulic Cylinders • Effective piston area is reduced on retraction due to the rod cross section.

  16. Hydraulic Cylinders • Telescoping cylinders are available for applications requiring long extension distances: • Rod is made up of several tubes of varying size nested inside of the barrel • Each tube extends, producing a rod longer than the cylinder barrel • Typical example is the actuator that raises the box on a dump truck

  17. Hydraulic Cylinders • Telescoping cylinders: • The maximum force is at the collapsed position • The speed will increase at each stage, but will not allow much force

  18. Hydraulic Cylinders • Cylinders often use hydraulic cushions (to brake high stroke speeds): • Provide a controlled approach to the end of the stroke • Reduces the shock of the impact as the piston contacts the cylinder head

  19. Hydraulic Cylinders • Cylinders with end position cushioning: • Cushioning is not required for speeds of v<6 m/min. • This type of end position cushioning is used for stroke speed between 6 m/min and 20 m/min. At higher speed, additional cushioning or braking devices must be used.

  20. Hydraulic Cylinders • A variety of mounting configurations are used to attach the cylinder body and rod end to machinery: • Fixed centerline • Fixed noncenterline • Pivoting centerline • Expected cylinder loading is the major factor in the selection of the mounting style.

  21. Hydraulic Cylinders • Head-end (Fixed centerline) flange mount

  22. Hydraulic Cylinders • Fixed-noncenterline mount

  23. Hydraulic Cylinders • Pivoting-centerline, clevis mount

  24. Hydraulic Cylinders • Pivoting-centerline, trunnion mount

  25. Hydraulic Cylinders • Types of mounting:

  26. Hydraulic Cylinders • The force generated by a cylinder is calculated by multiplying the effective area of the piston by the system pressure. • F=p.A • By consideration of mechanical efficiency:

  27. Hydraulic Cylinders • Cylinder characteristics

  28. Hydraulic Cylinders • Cylinder characteristics dp: cylinder dia. Ap: cylinder area dST: piston rod dia.

  29. Effective area Piston velocity Hydraulic Cylinders • Speed at which the cylinder extends or retracts is determined by: • Flow Rate (Q) • Effective Area (A) Q [m3/s] = A [m2] X  [m/s]

  30. Hydraulic Cylinders • Buckling resistance

  31. Hydraulic Cylinders • Selecting a cylinder (Example)

  32. Hydraulic Cylinders • Selecting a cylinder (Example)

  33. Hydraulic Cylinders • Selecting a cylinder (Example) Buckling resistance diagram: Reference: Festo Didactic Hydraulic

  34. Hydraulic Cylinders • Selecting a cylinder (Example)

  35. Hydraulic Cylinders • Selecting a cylinder (Example)

  36. Hydraulic Cylinders • Selecting a cylinder (Example)

  37. Hydraulic Cylinders • Hydraulic cylinder manufacturers provide detailed specifications and basic factors such as: • Bore • Stroke • Pressure rating • Other details, such as service rating, rod end configurations, and dimensions

  38. Hydraulic Cylinders • Typical manufacturer’s catalog page Bailey International Corporation

  39. Limited-Rotation Hydraulic Actuators • Limited-rotation devices (swivel drive) are actuators with an output shaft that typically applies torque through approximately 360° of rotation. • Models are available that are limited to less than one revolution, while others may produce several revolutions.

  40. Limited-Rotation Hydraulic Actuators • Most common designs of limited-rotation actuators are: • Rack-and-pinion • Vane • Helical piston and rod

  41. Limited-Rotation Hydraulic Actuators • Rack-and-pinion limited rotation actuator • Here maximum angle may be larger than 360°.

  42. Limited-Rotation Hydraulic Actuators • Vane limited-rotation actuator

  43. Limited-Rotation Hydraulic Actuators • Helical piston and rod limited-rotation actuator

  44. Limited-Rotation Hydraulic Actuators • Limited-rotation actuators are used to perform a number of functions in a variety of industrial situations: • Indexing devices on machine tools • Clamping of workpieces • Operation of large valves • Limited-rotation actuators are used in this robotic arm:

  45. Hydraulic Motors • Hydraulic motors are called rotary actuators. • They convert fluid pressure and flow into torque and rotational movement.

  46. Hydraulic Motors • System fluid enters the housing and applies pressure to the rotating internal parts. • This, in turn, moves the power output shaft and applies torque to rotate a load. • Primary parts that produce the rotating motion in most hydraulic motors are either: • Gears • Vanes • Pistons

  47. Hydraulic Motors • The external gear hydraulic motor is the most common and simplest of the basic motor types: • Unbalanced load on the bearings

  48. Hydraulic Motors • The most common internal gear motor has a gerotor design

  49. Hydraulic Motors • Basic vane motor (unbalanced)

  50. Hydraulic Motors • A basic, balanced vane motor