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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

Chapter 13

Applying Hydraulic Power

Typical Circuits and Systems

objectives
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.

objectives4
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.

objectives5
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.

basic circuits and their use in system analysis and design
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.

design and operation of basic pressure related circuits
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.

design and operation of basic pressure related circuits8
Design and Operation of Basic Pressure-Related Circuits
  • A basic pressure-control circuit

Permission granted to reproduce for educational use only.

design and operation of basic pressure related circuits9
Design and Operation of Basic Pressure-Related Circuits
  • Remote pressure control in a circuit

Permission granted to reproduce for educational use only.

slide10

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.

design and operation of basic pressure related circuits11
Design and Operation of Basic Pressure-Related Circuits
  • Multiple pressures in a circuit

Permission granted to reproduce for educational use only.

design and operation of basic pressure related circuits12
Design and Operation of Basic Pressure-Related Circuits
  • Reduced pressure in a circuit

Permission granted to reproduce for educational use only.

design and operation of basic pressure related circuits13
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.

design and operation of basic pressure related circuits14
Back-pressure check valveDesign and Operation of Basic Pressure-Related Circuits

Permission granted to reproduce for educational use only.

design and operation of basic flow related circuits
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.

design and operation of basic flow related circuits16
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.

design and operation of basic flow related circuits17
Design and Operation of Basic Flow-Related Circuits
  • Basic meter-in circuit

Permission granted to reproduce for educational use only.

design and operation of basic flow related circuits18
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.

design and operation of basic flow related circuits19
Design and Operation of Basic Flow-Related Circuits
  • Basic meter-out circuit

Permission granted to reproduce for educational use only.

design and operation of basic flow related circuits20
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.

design and operation of basic flow related circuits21
Design and Operation of Basic Flow-Related Circuits
  • Basic bleed-off circuit

Permission granted to reproduce for educational use only.

design and operation of basic flow related circuits22
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.

design and operation of basic flow related circuits23
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.

design and operation of basic flow related circuits24
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.

design and operation of other flow related circuits
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.

design and operation of other flow related circuits26
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.

design and operation of other flow related circuits27
Design and Operation of Other Flow-Related Circuits
  • High-low pump circuit

Permission granted to reproduce for educational use only.

design and operation of other flow related circuits28
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.

design and operation of other flow related circuits29
Design and Operation of Other Flow-Related Circuits
  • Regenerative-cylinder-advance circuit

Permission granted to reproduce for educational use only.

design and operation of other flow related circuits30
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.

design and operation of other flow related circuits31
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.

design and operation of other flow related circuits32
Design and Operation of Other Flow-Related Circuits
  • Application of a deceleration valve

Permission granted to reproduce for educational use only.

design and operation of basic motion related circuits
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.

design and operation of basic motion related circuits34
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.

design and operation of basic motion related circuits35
Design and Operation of Basic Motion-Related Circuits
  • Sequencing with spring-loaded check valves

Permission granted to reproduce for educational use only.

design and operation of basic motion related circuits36
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.

design and operation of basic motion related circuits37
Design and Operation of Basic Motion-Related Circuits
  • Sequencing with special valves

Permission granted to reproduce for educational use only.

design and operation of basic motion related circuits38
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.

design and operation of basic motion related circuits39
Design and Operation of Basic Motion-Related Circuits
  • Synchronization with accurate flow control valves

Permission granted to reproduce for educational use only.

design and operation of basic motion related circuits40
Design and Operation of Basic Motion-Related Circuits
  • Synchronization with mechanically coupled motors

Permission granted to reproduce for educational use only.

design and operation of circuits with other functions
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.

design and operation of circuits with other functions42
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.

design and operation of circuits with other functions44
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.

design and operation of circuits with other functions45
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.

design and operation of circuits with other functions46
Design and Operation of Circuits with Other Functions
  • Decompression circuit on a platen press

Permission granted to reproduce for educational use only.

design and operation of circuits with other functions47
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.

design and operation of circuits with other functions48
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.

design and operation of circuits with other functions49
Design and Operation of Circuits with Other Functions
  • Two-hand safety circuitfor machine operator safety

Permission granted to reproduce for educational use only.

review question
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.

review question51
Review Question

A maximum pressure lower than the system relief valve setting may be obtained in a portion of a circuit by using a(n) _____ valve.

pressure-reducing

Permission granted to reproduce for educational use only.

review question52
Review Question

Name the three characteristics of basic flow control circuits that need to be considered when selecting a design for use in a hydraulic system.

A. Accuracy of flow control, B. operating efficiency, and C. ability to control varying loads.

Permission granted to reproduce for educational use only.

review question53
Review Question

Which flow control circuit is considered the most energy efficient?

Bleed-off circuit.

Permission granted to reproduce for educational use only.

review question54
Review Question

Describe two methods that may be used to synchronize the movement of two or more hydraulic cylinders.

A. Use of two hydraulic motor with a mechanical coupling between their output shafts and B. use of accurate pressure-compensated flow control valves.

Permission granted to reproduce for educational use only.

review question55
Review Question

How is rapid cylinder advance created in a regenerative-cylinder-advance circuit?

Fluid from the rod end of the cylinder is directed to the blind end to increase the amount of fluid flow available to extend the cylinder.

Permission granted to reproduce for educational use only.

review question56
Review Question

Name three factors that hydraulic safety circuits ensure.

A. Equipment can be operated without injury, B. equipment cannot unexpectedly operate, and C. Costly equipment is protected against excessive pressure and operating rates.

Permission granted to reproduce for educational use only.