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Chapter 9

Chapter 9. Actuators. Workhorses of the System. Objectives. Describe the construction and operation of basic hydraulic cylinders, limited-rotation actuators, and motors. Compare the design and operation of various types of hydraulic cylinders.

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Chapter 9

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  1. Chapter 9 Actuators Workhorses of the System

  2. Objectives • Describe the construction and operation of basic hydraulic cylinders, limited-rotation actuators, and motors. • Compare the design and operation of various types of hydraulic cylinders. • Select appropriate cylinder design options available for mounting hydraulic cylinders and reducing hydraulic shock. • Compare the design and operation of various types of hydraulic motors. Permission granted to reproduce for educational use only.

  3. Objectives • Contrast the operation of fixed- and variable-speed hydraulic motors. • Describe the construction and operation of a basic hydrostatic transmission. • Size hydraulic cylinders and motors to correctly meet system force and speed requirements. • Interpret manufacturer specifications for hydraulic cylinders. Permission granted to reproduce for educational use only.

  4. 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 Permission granted to reproduce for educational use only.

  5. Hydraulic Cylinders • A basic cylinder consists of: • Piston • Piston rod • Barrel Permission granted to reproduce for educational use only.

  6. Hydraulic Cylinders • Parts of a typical cylinder Permission granted to reproduce for educational use only.

  7. Hydraulic Cylinders • The piston forms sealed, variable-volume chambers in the cylinder • System fluid forced into the chambers drives the piston and rod assembly • Linear movement is produced Permission granted to reproduce for educational use only.

  8. Hydraulic Cylinders • Seals prevent leakage between: • Piston and cylinder barrel • Piston rod and head • Barrel and its endpieces • Wiper seal, or scraper, prevents dirt and water from entering the cylinder during rod retraction Permission granted to reproduce for educational use only.

  9. Hydraulic Cylinders • Various seals are used in a cylinder Permission granted to reproduce for educational use only.

  10. Rod wipers prevent contamination from entering on rod retraction Hydraulic Cylinders IMI Norgren, Inc. Permission granted to reproduce for educational use only.

  11. Hydraulic Cylinders • Cylinders are typically classified by operating principle or by construction type • Single-acting or double-acting • Tie rod, mill, threaded end, or one piece Permission granted to reproduce for educational use only.

  12. Hydraulic Cylinders • Single- and double-acting cylinders Single-acting Double-acting Permission granted to reproduce for educational use only.

  13. Hydraulic Cylinders • Single-acting cylinders exert force either on extension or retraction • They require an outside force to complete the second motion Permission granted to reproduce for educational use only.

  14. Hydraulic Cylinders • Double-acting cylinders 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 Permission granted to reproduce for educational use only.

  15. Hydraulic Cylinders • Effective piston area is reduced on retraction due to the rod cross section Permission granted to reproduce for educational use only.

  16. Hydraulic Cylinders • Volume is reduced on retraction Permission granted to reproduce for educational use only.

  17. Hydraulic Cylinders • External tie rod bolts are used to secure the ends on the tie-rod cylinder design • Commonly found on heavy industrial machines • External tie rods increase chance of damage and promote accumulation of dirt Permission granted to reproduce for educational use only.

  18. Hydraulic Cylinders • Tie-rod cylinder Permission granted to reproduce for educational use only.

  19. Hydraulic Cylinders • Mill cylinders Yates Industries, Inc. Permission granted to reproduce for educational use only.

  20. Hydraulic Cylinders • Threaded-end cylinder Bailey International Corporation Permission granted to reproduce for educational use only.

  21. Hydraulic Cylinders • One-piece cylinder has the cylinder barrel welded to the ends • Produces a compact actuator • Cost effective to manufacture • Cannot be serviced (throwaway) Permission granted to reproduce for educational use only.

  22. Hydraulic Cylinders • Hydraulic ram is commonly used in hand-operated jacks • Rod is basically the same diameter as the inside of the cylinder barrel • Large-diameter rod is more rigid under load, but cylinder can generate force in only one direction Permission granted to reproduce for educational use only.

  23. Typical hand-operated jack Hydraulic Cylinders Permission granted to reproduce for educational use only.

  24. 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 Permission granted to reproduce for educational use only.

  25. Hydraulic Cylinders • Telescoping cylinders Star Hydraulics, Inc. Permission granted to reproduce for educational use only.

  26. Hydraulic Cylinders • Cylinders often use hydraulic cushions • Provide a controlled approach to the end of the stroke • Reduces the shock of the impact as the piston contacts the cylinder head Permission granted to reproduce for educational use only.

  27. Hydraulic Cylinders • Cylinder cushioning device Permission granted to reproduce for educational use only.

  28. 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 Permission granted to reproduce for educational use only.

  29. Hydraulic Cylinders • Head-end flange mount Permission granted to reproduce for educational use only.

  30. Hydraulic Cylinders • Fixed-noncenterline mount Permission granted to reproduce for educational use only.

  31. Hydraulic Cylinders • Pivoting-centerline, clevis mount Permission granted to reproduce for educational use only.

  32. Hydraulic Cylinders • Pivoting-centerline, trunnion mount Permission granted to reproduce for educational use only.

  33. Hydraulic Cylinders • The force generated by a cylinder is calculated by multiplying the effective area of the piston by the system pressure Permission granted to reproduce for educational use only.

  34. Hydraulic Cylinders • Effective cylinder piston area Permission granted to reproduce for educational use only.

  35. Hydraulic Cylinders • Force generated during the extension of a double-acting cylinder with a single-ended rod is calculated as: Ef = Sp  Pawhere:Ef = extension forceSp = system pressurePa = piston area (Calculations require consistent units of measure in these formulas) Permission granted to reproduce for educational use only.

  36. Hydraulic Cylinders • Force generated during the retraction of a double-acting cylinder with a single-ended rod is calculated as:Rf = Sp  (Pa – Ra)where:Rf = retraction forceSp = system pressurePa = piston areaRa = rod area Permission granted to reproduce for educational use only.

  37. Hydraulic Cylinders • Speed at which the cylinder extends or retracts is determined by: • Physical volume per inch of cylinder piston travel • Amount of fluid entering the cylinder • Effective area of the piston is used to calculate the volume of the cylinder per inch of piston travel Permission granted to reproduce for educational use only.

  38. Hydraulic Cylinders • Extension speed of a double-acting cylinder with a single-ended rod is calculated as:Es = Fr  (Cg  Pa)where:Es = extension speedFr = flow delivery rateCg = cubic inches in one gallonPa = piston area Permission granted to reproduce for educational use only.

  39. Hydraulic Cylinders • Calculate retraction speed of a double-acting cylinder with single-ended rod as:Rs = Fr  [Cg  (Pa – Ra)]where:Rs = retraction speedFr = flow delivery rateCg = cubic inches in one gallonPa = piston areaRa = rod area Permission granted to reproduce for educational use only.

  40. Hydraulic Cylinders • Flow rate to produce a desired extension or retraction speed is calculated as:Fr = (Ea  Cs)  Cgwhere:Fr = system flow rateEa = effective piston areaCs = cylinder speedCg = cubic inches in one gallon Permission granted to reproduce for educational use only.

  41. Hydraulic Cylinders • Hydraulic cylinder manufacturers provide detailed specifications concerning: • Construction • Physical size • Load capacity Permission granted to reproduce for educational use only.

  42. Hydraulic Cylinders • This information includes basic factors such as: • Bore • Stroke • Pressure rating • Other details, such as service rating, rod end configurations, and dimensions Permission granted to reproduce for educational use only.

  43. Hydraulic Cylinders • Typical manufacturer’s catalog page Bailey International Corporation Permission granted to reproduce for educational use only.

  44. Limited-RotationHydraulic Actuators • Limited-rotation devices 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 Permission granted to reproduce for educational use only.

  45. Limited-RotationHydraulic Actuators • Most common designs of limited-rotation actuators are: • Rack-and-pinion • Vane • Helical piston and rod Permission granted to reproduce for educational use only.

  46. Limited-RotationHydraulic Actuators • Rack-and-pinion limited rotation actuator IMI Norgren, Inc. Permission granted to reproduce for educational use only.

  47. Limited-RotationHydraulic Actuators • Vane limited-rotation actuator Permission granted to reproduce for educational use only.

  48. Limited-RotationHydraulic Actuators • Helical piston and rod limited-rotation actuator Permission granted to reproduce for educational use only.

  49. Limited-RotationHydraulic 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 Permission granted to reproduce for educational use only.

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