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Chapter 13

Chapter 13. Applying Hydraulic Power. Typical Circuits and Systems. Objectives. Name common, basic subsystems that compose complex hydraulic systems and describe their function. Compare the design and operation of basic pressure control circuits.

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Chapter 13

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  1. Chapter 13 Applying Hydraulic Power Typical Circuits and Systems

  2. Objectives • Name common, basic subsystems that compose complex hydraulic systems and describe their function. • Compare the design and operation of basic pressure control circuits. • Contrast the operating characteristics of meter-in, meter-out, and bleed-off flow control circuits. Permission granted to reproduce for educational use only.

  3. Objectives • Compare the design and operation of several typical flow control circuits. • Compare the design and operation of basic motion control circuits. • Describe the design and operation of rapid-advance-to-work circuits. Permission granted to reproduce for educational use only.

  4. Objectives • Describe various hydraulic circuits designed to provide for operator safety and the protection of system components. Permission granted to reproduce for educational use only.

  5. Basic Circuits and Their Use in System Analysis and Design • Hydraulic systems involve a group of components that closely work together to produce a desired performance • Pressure control • Flow control • Motion control • Miscellaneous functions • A hydraulic system typically includes several of these segments Permission granted to reproduce for educational use only.

  6. Design and Operation of Basic Pressure-Related Circuits • Basic pressure-control circuits limit the maximum operating pressure of a hydraulic system • Variations of this function include circuits that can: • Control pressure from a remote location • Provide for the selection of multiple pressures in a single circuit Permission granted to reproduce for educational use only.

  7. Design and Operation of Basic Pressure-Related Circuits • A basic pressure-control circuit Permission granted to reproduce for educational use only.

  8. Design and Operation of Basic Pressure-Related Circuits • Remote pressure control in a circuit Permission granted to reproduce for educational use only.

  9. Design and Operation of BasicPressure-Related Circuits • Multiple operating pressures can be achieved for a system by using a compound relief valve • The venting feature is combined with additional low-flow-capacity, direct-operated relief valves Permission granted to reproduce for educational use only.

  10. Design and Operation of Basic Pressure-Related Circuits • Multiple pressures in a circuit Permission granted to reproduce for educational use only.

  11. Design and Operation of Basic Pressure-Related Circuits • Reduced pressure in a circuit Permission granted to reproduce for educational use only.

  12. Design and Operation of Basic Pressure-Related Circuits • With open- and tandem-center directional control valves, a spring-loaded check valve may be placed in the return line to create low back pressure • Maintains low system pressure necessary to operate pilot-controlled functions • This variation still produces an energy-efficient circuit that is a feature of these valve center designs Permission granted to reproduce for educational use only.

  13. Back-pressure check valve Design and Operation of Basic Pressure-Related Circuits Permission granted to reproduce for educational use only.

  14. Design and Operation of Basic Flow-Related Circuits • Three basic flow control circuits are used in hydraulic systems: • Meter in • Meter out • Bleed off • These basic circuits meet the varying flow-control demands for systems with positive and negative loads Permission granted to reproduce for educational use only.

  15. Design and Operation of Basic Flow-Related Circuits • The meter-in flow control design places the flow control valve between the pump and the inlet of the actuator • Should only be used for positive loads • Cannot provide accurate control under a negative load condition • The prime mover is always operating against the maximum pressure setting of the system relief valve Permission granted to reproduce for educational use only.

  16. Design and Operation of Basic Flow-Related Circuits • Basic meter-in circuit Permission granted to reproduce for educational use only.

  17. Design and Operation of Basic Flow-Related Circuits • The meter-out flow control design places the flow control valve between the actuator outlet and the reservoir • Can provide accurate control for positive and negative loads • The prime mover is always operating against the maximum pressure setting of the system relief valve Permission granted to reproduce for educational use only.

  18. Design and Operation of Basic Flow-Related Circuits • Basic meter-out circuit Permission granted to reproduce for educational use only.

  19. Design and Operation of Basic Flow-Related Circuits • The bleed-off flow control design places the flow control valve in a tee in the working line between the directional control valve and the actuator inlet • Outlet of the flow control is directly connected to the reservoir • Measured flow is diverted to the reservoir while remaining flow operates the actuator • The prime mover operates against a pressure only high enough to move the load Permission granted to reproduce for educational use only.

  20. Design and Operation of Basic Flow-Related Circuits • Basic bleed-off circuit Permission granted to reproduce for educational use only.

  21. Design and Operation of Basic Flow-Related Circuits • Meter-in and meter-out circuits provide the most accurate actuator speeds • Both meter fluid flow delivered directly to or from the actuator • The meter-out circuit is the best method for negative loads that may pull the actuator Permission granted to reproduce for educational use only.

  22. Design and Operation of Basic Flow-Related Circuits • The bleed-off flow control circuit is less accurate than either the meter-in or meter-out system • Flow is metered back to the reservoir while the remaining pump output establishes actuator speed • The remaining flow can vary because of pump efficiency and system leakage • Flow control valve metering accuracy under varying load conditions is also a factor Permission granted to reproduce for educational use only.

  23. Design and Operation of Basic Flow-Related Circuits • The bleed-off circuit is the most energy-efficient design • This is due to the fact the prime mover operates at a pressure only high enough to move the load Permission granted to reproduce for educational use only.

  24. Design and Operation of Other Flow-Related Circuits • Several other circuit designs can also be used to control flow to a circuit actuator • High-low pump circuit • Regenerative-cylinder-advance circuit • Rapid-advance-to-work circuit Permission granted to reproduce for educational use only.

  25. Design and Operation of Other Flow-Related Circuits • The high-low pump circuit allows a system to use two pumps in tandem • Provides high-volume flow during low-pressure demand • Provides low-volume flow during high-pressure demand • Lowers equipment costs by reducing prime mover size and cuts ongoing system energy consumption Permission granted to reproduce for educational use only.

  26. Design and Operation of Other Flow-Related Circuits • High-low pump circuit Permission granted to reproduce for educational use only.

  27. Design and Operation of Other Flow-Related Circuits • A regenerative-cylinder-advance circuit provides a rapid advance to the point where a load is encountered • Fluid is recirculated from the rod end into the blind end and coupled with pump output to increase flow into the blind end, thus increasing cylinder extension speed • Recirculation is possible due to the difference in area between the cylinder piston ends Permission granted to reproduce for educational use only.

  28. Design and Operation of Other Flow-Related Circuits • Regenerative-cylinder-advance circuit Permission granted to reproduce for educational use only.

  29. Design and Operation of Other Flow-Related Circuits • During the rapid-extension phase of a regenerative circuit, the effective force is limited to the maximum pressure setting of the system multiplied by the cross-sectional area of the cylinder rod Permission granted to reproduce for educational use only.

  30. Design and Operation of Other Flow-Related Circuits • A mechanically activated deceleration valve is often used in rapid-advance-to-work circuits • This controls the rate at which the advancing cylinder is slowed from the rapid-advance speed to the slower feed rate Permission granted to reproduce for educational use only.

  31. Design and Operation of Other Flow-Related Circuits • Application of a deceleration valve Permission granted to reproduce for educational use only.

  32. Design and Operation of Basic Motion-Related Circuits • Sequence circuits operate actuators in a specific order • Two common methods for actuator sequencing are: • Spring-loaded check valves • Specially designed sequence valves Permission granted to reproduce for educational use only.

  33. Design and Operation of Basic Motion-Related Circuits • Check valves are inexpensive • Valves designed for specific sequence control provide more accurate movement Permission granted to reproduce for educational use only.

  34. Design and Operation of Basic Motion-Related Circuits • Sequencing with spring-loaded check valves Permission granted to reproduce for educational use only.

  35. Design and Operation of Basic Motion-Related Circuits • Specially constructed pressure control valves can be used to sequentially block fluid flow to actuators • When a preselected pressure is reached, these valves open to allow fluid flow to the actuator • This provides the order of operation • Check valves allow reverse flow around these pressure control valves Permission granted to reproduce for educational use only.

  36. Design and Operation of Basic Motion-Related Circuits • Sequencing with special valves Permission granted to reproduce for educational use only.

  37. Design and Operation of Basic Motion-Related Circuits • Synchronizing the movement of cylinders requires accurately metering fluid flow into the actuators • Accurate flow control valves • Other metering devices, such as mechanically connected hydraulic motors Permission granted to reproduce for educational use only.

  38. Design and Operation of Basic Motion-Related Circuits • Synchronization with accurate flow control valves Permission granted to reproduce for educational use only.

  39. Design and Operation of Basic Motion-Related Circuits • Synchronization with mechanically coupled motors Permission granted to reproduce for educational use only.

  40. Design and Operation of Circuits with Other Functions • Two factors that are basic to motor operation are: • Fluid flow rate establishes motor speed • Pressure establishes torque output • Other factors must also be considered: • Motor freewheeling • Motor braking Permission granted to reproduce for educational use only.

  41. Design and Operation of Circuits with Other Functions • Motor control circuits with a three-position directional control valve can allow a hydraulic motor to: • Rotate with full speed and torque capability • Freewheel using the inertia of the load to sustain rotation • Brake to a stop under controlled conditions Permission granted to reproduce for educational use only.

  42. Circuit allowing a motor to be powered, braked, or to freewheel Design and Operation of Circuits with Other Functions Permission granted to reproduce for educational use only.

  43. Design and Operation of Circuits with Other Functions • Decompression circuits release the pressures from the expansion and contraction of components and the external loading of actuators • These high pressures can exist even when the power unit is not operating • Decompression is for both operator safety and the continued functioning of the system Permission granted to reproduce for educational use only.

  44. Design and Operation of Circuits with Other Functions • Decompression circuits often use staged, pilot-operated check valves • Pressurizing the first stage opens a small orifice that quickly reduces the high system pressure • The pilot mechanism continues to open the check valve, exposing a larger orifice that allows the rapid movement of system fluid to the reservoir Permission granted to reproduce for educational use only.

  45. Design and Operation of Circuits with Other Functions • Decompression circuit on a platen press Permission granted to reproduce for educational use only.

  46. Design and Operation of Circuits with Other Functions • Safety is always a factor when designing hydraulic circuits • High pressures • High fluid flow rated • Substantial forces • Rapid movement of system components • Inappropriate use of any of these elements can produce a dangerous work situation for a machine operator Permission granted to reproduce for educational use only.

  47. Design and Operation of Circuits with Other Functions • Safety-related circuits ensure: • Equipment can be operated without injury • Equipment cannot unexpectedly operate • Costly equipment is protected against excessive pressure and operating rates Permission granted to reproduce for educational use only.

  48. Design and Operation of Circuits with Other Functions • Two-hand safety circuitfor machine operator safety Permission granted to reproduce for educational use only.

  49. Review Question Remote control of pilot-operated relief valves can be easily achieved by using the _____ feature of the valve. vent Permission granted to reproduce for educational use only.

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