Electrohydraulics

TWO ELECTROHYDRAULIC VALVES
DESCRIPTION OF VALVES
Electrohydraulic Control
Proportional Solenoid Devices
ELECTROHYDRAULIC FLOW CONTROL VALVES
Flow Control
Torque Motor Devices
Nozzle Flapper Valve
Nozzle Flapper Two-Stage Valve
Jet Pipe Two-Stage Valve
Three-Stage Valves
Load Independent Flow Control Valves

THREE SELECTION OF VALVES
INTRODUCTION
VALVE CHARACTERISTICS AND TEST METHODS
Flow Characteristics
Pressure Gain
Lap Condition
Effect of System Pressure
Load Pressure Drop
Quiescent or Leakage Flow
Dynamic Performance
Null Shifts and Hysteresis
Hysteresis
Linearity, Resolution and Threshold
Proof Pressure, Endurance, Impulse and Environmental Tests
Electrical characteristics
THE CHOICE OF THE VALVE (SYSTEM CONSIDERATIONS)
Type of Actuator
Single Rod Actuators
Single Rod Actuators with Symmetrical Valves
Three-Port and Regenerative Systems
Single Rod Actuator with Asymmetrical Valve
Double Rod Actuators
Motors and Rotary Actuators
Supply Pressure
Actuator Size
Valve Pressure Drop
Valve Flow Rate
Valve Dynamic Response
Valve Null Characteristics
Null Position vs. De-energised Position
Valve Lap Conditions
Pressure Gain
Null Shifts
De-energised Operation
Linearity
Hysteresis, Threshold and Resolution

FOUR OPEN-LOOP SYSTEM CALCULATIONS
INTRODUCTION
Scope and Limitations
CALCULATION METHOD
Calculate Net Force on Actuator
Calculate Required Supply Pressure
Calculation of Valve Pressure Drops
Calculate valve pressure drop - Actuator extending
Calculate valve pressure drop - Actuator retracting
Check Valve Pressure Drop
Calculate Actuator Pressures
Calculate Minimum Valve Rated Flow
Calculate Actuator Velocity for Maximum Valve Opening
WORKED EXAMPLE
Calculate Required Supply Pressure
Calculation of Valve Pressure Drops
Calculate valve pressure drop - Actuator extending
Calculate valve pressure drop - Actuator retracting
Check Valve Pressure Drop
Calculate Actuator Pressure
Calculate Minimum Valve Rated Flow
Calculate Maximum Valve Input Signal

FIVE PERFORMANCE PREDICTION OF CLOSED-LOOP SYSTEMS
INTRODUCTION
Scope and Limitations
Overview of the Design Process
SYSTEM COMPONENTS AND THEIR OPERATION
The Electrohydraulic Valve
The Actuator
The Position Sensor
The Position Comparator
The Electrical Gain and Limiter Block
THE TRAPEZOIDAL VELOCITY PROFILE
The First Phase
The Second Phase
The Third Phase
LIMITS ON MAXIMUM GAIN DUE TO COMPRESSIBILITY
Calculate Oil Spring Stiffness
Calculate Oil Spring Natural Frequency
Calculate a New Electrical Gain Based on Actuator Stiffness
Select the Lower Gain
ACTUATOR POSITION ERRORS
Calculate Pressure to Start Actuator Motion
Calculate Valve Input Volts
FOLLOWING ERROR
THE SUBSTITUTION RULES
OBSERVATIONS REGARDING OPEN-LOOP SYSTEMS
WORKED EXAMPLE
Maximum Electrical Gain
Calculate Oil Stiffness
Calculate Actuator Natural Frequency
Calculate a New Electrical Gain
Calculate Maximum Velocity
Maximum Flow
Calculate Volts to Produce Maximum Flow
Calculate the Attenuator Gains and Modified Valve Parameters
Calculate the Required Pressure Difference
Calculate Voltage Required to Start Actuator Motion
Calculate the Maximum Actuator Errors for each Direction
Calculate the Error Amplitude after Commissioning

SIX AMPLIFIERS
DRIVE AMPLIFIERS
AMPLIFIER FORMATS
Eurocard Amplifiers
Valve-mounted Amplifiers
ENVIRONMENT
Moisture, Humidity and Dust
Vibration
Temperature Range
Cooling Requirements
Power Supply Requirements
INSTALLATION GUIDELINES
AMPLIFIER FEATURES AND FUNCTIONS
Input Signal Requirements
Input Potentiometers
Current Inputs
Switched Preset Inputs
Input Signal Scaling
Null Adjustment (Offset)
Ramps
Ramp Enable/Disable
Deadband Compensation
Signal Monitor Points
Output Enable/Disable (Inhibit)
Detection of Loss of Feedback Signals
Current Limiting (Short Circuit Protection)
Error Output Signal
LED Fault Indicators
SYSTEM DESIGN AND CONSTRUCTION
Standards and Directives
Temperature, Humidity and Vibration
Electromagnetic Compatibility
Emissions
Immunity
Power Supply Faults
REFERENCES 77

SEVEN SENSORS
GENERAL
ANALOGUE POSITION SENSORS
Potentiometers
Linear Variable Differential Transformer (LVDT)
General
Construction
Eddy Current Devices
Hall Effect Sensors
Magnetostrictive (Strain Wave) Position Sensors
Capacitive Sensors
ANALOGUE VELOCITY SENSORS
Tachogenerators
Induction Tachometers
ACCELERATION SENSORS
FORCE SENSORS
Load Cells
PRESSURE TRANSDUCERS
DIGITAL POSITION SENSORS
Definition
Incremental Encoders
ABSOLUTE POSITION ENCODERS
Advantages and Disadvantages
DIGITAL VELOCITY SENSORS
Digital Tachogenerators

EIGHT PRESSURE CONTROLS (TYPES) 1 PRESSURE CONTROL

NINE SELECTION OF PRESSURE CONTROLS
SCOPE
Relief Valve Operation and Use
Reducing Valve Operation and Use
PERFORMANCE CHARACTERISTICS INTRODUCTION
STEADY STATE PERFORMANCE CHARACTERISTICS
Maximum Flow
Minimum Flow
Reverse Flow (Reducing Valves Only)
Reverse Flow to Inlet
Reverse Flow to Tank
Maximum Pressure
Minimum Pressure
Pressure/Flow Characteristic (Relief Valve)
Pressure/Flow Characteristic (Reducing Valves)
Linearity
Hysteresis and Dither
DYNAMIC PERFORMANCE CHARACTERISTICS
Frequency Response (Current to Pressure)
Frequency Response (Flow to Pressure)
Step Response
Step Response (Relief Valves)
Step Response (Reducing Valves)
RATED PRESSURE
ELECTRICAL INTERFACE
REFERENCES

TEN THE APPLICATION OF ELECTROHYDRAULIC VALVES
INTRODUCTION
MANUFACTURING AND PROCESS CONTROL
Force Control Presses
Speed and Force Control in Plastic Processing
Rug Manufacturing
MECHANICAL HANDLING
Lift/Lower Controls for Lift Trucks
Glass Transporter
AUTOMOTIVE AND RAIL TRANSPORT
Engine Cooling Fan Drive
MARINE AND OFFSHORE
Offshore Escape Gangway
Stabilisation of a Ship-Mounted Derrick
MOBILE EQUIPMENT
Access Platforms
Electronic Load Control of Excavators
MINING AND TUNNELLING
Mining Haulage Control System
CIVIL ENGINEERING
Lift Bridge
METAL INDUSTRY
Strip Edge Guidance
Roller Position Control System
Continuous Strand Casting Plant
THE TEST EQUIPMENT
Hydraulic Damper Test Equipment
A High-Rate Impact Tester
Precise Speed Control of a Centrifuge
REFERENCES

ELEVEN REFERENCE SECTION GLOSSARY OF TERMS
RECOMMENDED SYMBOLS AND UNITS
READING LIST

INDEX

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