Hydraulics_elHydr_FESTO_textbook

Hydraulics
Electrohydraulics

Fundamentals

Textbook

AB
M1 M2

PT

T BPA

Festo Didactic
574181 en

Order no. 574181
Revision level: 08/2013
Authors: Renate Aheimer, Christine Löffler, Dieter Merkle, Georg Prede,
Klaus Rupp, Dieter Scholz, Burkhard Schrader
Editor: Frank Ebel
Graphics: Doris Schwarzenberger
Layout: 09/2013, Frank Ebel

© Festo Didactic GmbH & Co. KG, 73770 Denkendorf, Germany, 2013
Internet: www.festo-didactic.com
E-mail: [email protected]

Reproduction, distribution and utilisation of this document, as well as the communication of its contents to
others without explicit authorisation, is prohibited. Offenders shall be held liable for damages. All rights
reserved, in particular the right to file patent, utility model and registered design applications.

Contents

Preface ________________________________________________________________________________ 10

1 The functions of a hydraulic system__________________________________________________ 11
1.1 Hydraulics – what does it mean? _____________________________________________________ 11
1.2 Stationary hydraulics ______________________________________________________________ 11
1.3 Mobile hydraulics _________________________________________________________________ 12
1.4 Attributes of hydraulics ____________________________________________________________ 13

2 Physical fundamentals of hydraulics _________________________________________________ 15
2.1 Pressure ________________________________________________________________________ 15
2.2 Pressure transmission _____________________________________________________________ 18
2.3 Force transmission ________________________________________________________________ 19
2.4 Displacement ratio ________________________________________________________________ 20
2.5 Pressure boosting_________________________________________________________________ 21
2.6 Volumetric flow rate _______________________________________________________________ 22
2.7 Continuity equation _______________________________________________________________ 22
2.8 Pressure measurement ____________________________________________________________ 23
2.9 Temperature measurement _________________________________________________________ 24
2.10 Volumetric flow rate measurement ___________________________________________________ 24
2.11 Types of flow_____________________________________________________________________ 25
2.12 Friction, heat, pressure drop ________________________________________________________ 27
2.13 Energy and power _________________________________________________________________ 31
2.13.1 Energy __________________________________________________________________________ 31
2.13.2 Power __________________________________________________________________________ 34
2.14 Cavitation _______________________________________________________________________ 37
2.15 Throttle points ___________________________________________________________________ 38

3 Hydraulic fluids __________________________________________________________________ 40
3.1 Functions of hydraulic fluids ________________________________________________________ 40
3.2 Types of hydraulic fluid ____________________________________________________________ 41
3.3 Characteristics and requirements ____________________________________________________ 42
3.4 Viscosity ________________________________________________________________________ 43

4 Components of the power supply section _____________________________________________ 47
4.1 Drive ___________________________________________________________________________ 47
4.2 Pump ___________________________________________________________________________ 48
4.3 Couplings _______________________________________________________________________ 55
4.4 Tanks ___________________________________________________________________________ 55
4.5 Filters___________________________________________________________________________ 57
4.5.1 Return filter ______________________________________________________________________ 59

© Festo Didactic GmbH & Co. KG 574181 3

Contents

4.5.2 Intake filters _____________________________________________________________________ 59
4.5.3 Pressure filters ___________________________________________________________________ 60
4.5.4 Filter arrangement ________________________________________________________________ 60
4.5.5 Bypass filtering ___________________________________________________________________ 63
4.5.6 Contamination indicators ___________________________________________________________ 63
4.5.7 Determining the differential pressure of a pressure filter _________________________________ 64
4.6 Cooling _________________________________________________________________________ 65
4.7 Heating _________________________________________________________________________ 66
4.8 Hydraulic accumulators ____________________________________________________________ 67
4.8.1 Design and mode of operation_______________________________________________________ 67
4.8.2 Piston accumulators _______________________________________________________________ 69
4.8.3 Diaphragm accumulators ___________________________________________________________ 70
4.8.4 Bladder accumulators _____________________________________________________________ 71
4.8.5 Safety regulations_________________________________________________________________ 72
4.8.6 Safety Equipment _________________________________________________________________ 73

5 Drives __________________________________________________________________________ 74
5.1 Hydraulic cylinders ________________________________________________________________ 74
5.1.1 Single-acting cylinders _____________________________________________________________ 74
5.1.2 Double-acting cylinders ____________________________________________________________ 75
5.1.3 End-position cushioning____________________________________________________________ 78
5.1.4 Seals ___________________________________________________________________________ 79
5.1.5 Mounting options _________________________________________________________________ 80
5.1.6 Exhaust _________________________________________________________________________ 80
5.1.7 Characteristic data ________________________________________________________________ 80
5.1.8 Resistance to buckling _____________________________________________________________ 82
5.1.9 Selecting a cylinder _______________________________________________________________ 84
5.2 Hydraulic motors _________________________________________________________________ 85

6 Characteristic values and designs of hydraulic valves ___________________________________ 88
6.1 Characteristic values of valves_______________________________________________________ 88
6.2 Actuating force ___________________________________________________________________ 89
6.3 Designs _________________________________________________________________________ 89
6.3.1 Poppet valves ____________________________________________________________________ 90
6.3.2 Slide valves ______________________________________________________________________ 91
6.4 Switching overlap _________________________________________________________________ 92
6.5 Control edges ____________________________________________________________________ 94

7 Pressure regulators _______________________________________________________________ 95
7.1 Pressure-relief valves ______________________________________________________________ 95
7.2 Pressure-reducing valves ___________________________________________________________ 97

4 © Festo Didactic GmbH & Co. KG 574181

Contents

8 Directional control valves _________________________________________________________ 100
8.1 Functions_______________________________________________________________________ 100
8.2 Design _________________________________________________________________________ 100
8.2.1 Directional control valve designs____________________________________________________ 100
8.2.2 Connection options for directional control valves ______________________________________ 102
8.2.3 Performance data for 4/3-way solenoid valves ________________________________________ 103
8.3 Actuation methods for directional control valves _______________________________________ 103
8.3.1 Manually and mechanically actuated directional control valves ___________________________ 104
8.3.2 Solenoid actuated directional control valves __________________________________________ 105
8.3.3 Power failures and wire breaks with solenoid actuated directional control valves ____________ 105
8.4 2/2-way valves __________________________________________________________________ 106
8.4.1 2/2-way stem actuated valve_______________________________________________________ 106
8.5 3/2-way valves __________________________________________________________________ 107
8.5.1 Directly actuated 3/2-way solenoid valve with spring return______________________________ 108
8.6 4/2-way valves __________________________________________________________________ 109
8.6.1 Transitional positions _____________________________________________________________ 110
8.6.2 4/2-way hand lever valve with spring return __________________________________________ 110
8.6.3 Directly actuated 4/2-way double solenoid valve with detent_____________________________ 111
8.7 4/3-way valves __________________________________________________________________ 112
8.7.1 4/3-way solenoid valve, spring centred, mid-position closed _____________________________ 113
8.7.2 Influence of the mid-position _______________________________________________________ 115
8.8 Pilot control of a directional control valve_____________________________________________ 116
8.8.1 Piloted 4/3-way solenoid valve _____________________________________________________ 116
8.8.2 Comparison of piloted and directly actuated solenoid valves _____________________________ 118

9 Shut-off valves __________________________________________________________________ 119
9.1 Non-return valve _________________________________________________________________ 119
9.2 Piloted non-return valve___________________________________________________________ 120
9.3 Piloted double non-return valve ____________________________________________________ 122

10 Flow control valves ______________________________________________________________ 123
10.1 Flow control and orifice valves______________________________________________________ 123
10.2 One-way flow control valve ________________________________________________________ 126
10.3 Flow control valves _______________________________________________________________ 127

11 Proportional valves ______________________________________________________________ 132
11.1 Design and function of a proportional solenoid ________________________________________ 132
11.1.1 Design of a proportional solenoid ___________________________________________________ 132
11.1.2 Function of a proportional solenoid__________________________________________________ 132
11.1.3 Actuation of pressure, flow control and directional control valves _________________________ 133
11.1.4 Armature position control _________________________________________________________ 134

© Festo Didactic GmbH & Co. KG 574181 5

Contents

11.2 Design and function of proportional pressure regulators ________________________________ 135
11.2.1 Pressure-relief valve ______________________________________________________________ 135
11.2.2 Pressure-reducing valve___________________________________________________________ 136
11.3 Design and function of proportional flow control valves and directional control valves ________ 137
11.3.1 Proportional flow control valves ____________________________________________________ 137
11.3.2 Directly actuated proportional directional control valve _________________________________ 137
11.3.3 Piloted proportional directional control valve__________________________________________ 138
11.3.4 Advantages and disadvantages of piloted proportional valves ____________________________ 139
11.4 Proportional valve designs_________________________________________________________ 140

12 Accessories_____________________________________________________________________ 141
12.1 Hoses and piping ________________________________________________________________ 141
12.1.1 Hoses__________________________________________________________________________ 142
12.1.2 Piping _________________________________________________________________________ 147
12.2 Connecting plates ________________________________________________________________ 149
12.3 Exhaust valves __________________________________________________________________ 150
12.4 Pressure gauges _________________________________________________________________ 151
12.4.1 Pressure gauge with Bourdon tube measuring unit _____________________________________ 151
12.4.2 Pressure gauge with capsule-type or diaphragm element ________________________________ 152
12.4.3 Piston-type pressure gauge ________________________________________________________ 152
12.5 Pressure sensors ________________________________________________________________ 153
12.6 Volumetric flow meters ___________________________________________________________ 153
12.6.1 Flow meter______________________________________________________________________ 153

13 Basic principles of electrical engineering ____________________________________________ 155
13.1 Direct current and alternating current ________________________________________________ 155
13.2 Ohm’s law ______________________________________________________________________ 156
13.2.1 Electrical conductors _____________________________________________________________ 156
13.2.2 Electrical resistance ______________________________________________________________ 156
13.2.3 Source voltage __________________________________________________________________ 157
13.3 Electrical power _________________________________________________________________ 157
13.4 The function of a solenoid _________________________________________________________ 158
13.4.1 Structure of a solenoid ____________________________________________________________ 158
13.4.2 Solenoid applications_____________________________________________________________ 158
13.4.3 Inductive resistance with AC voltage _________________________________________________ 159
13.4.4 Inductive resistance with DC voltage_________________________________________________ 159
13.5 Function of an electrical capacitor ___________________________________________________ 159
13.6 Function of a diode _______________________________________________________________ 160

6 © Festo Didactic GmbH & Co. KG 574181

Contents

13.7 Measurements in an electrical circuit ________________________________________________ 161
13.7.1 Definition: measure ______________________________________________________________ 161
13.7.2 Safety instructions _______________________________________________________________ 161
13.7.3 Procedure for performing measurements in the electrical circuit __________________________ 162
13.7.4 Voltage measurement ____________________________________________________________ 162
13.7.5 Current measurement_____________________________________________________________ 163
13.7.6 Resistance measurement __________________________________________________________ 163
13.7.7 Error sources while performing measurements in an electrical circuit ______________________ 164

14 Electrical components ____________________________________________________________ 165
14.1 Power pack _____________________________________________________________________ 165
14.2 Electrical input elements __________________________________________________________ 165
14.2.1 NO contact _____________________________________________________________________ 166
14.2.2 NC contact ______________________________________________________________________ 166
14.2.3 Changeover contact ______________________________________________________________ 166
14.3 Sensors ________________________________________________________________________ 167
14.3.1 Limit switches ___________________________________________________________________ 167
14.3.2 Proximity sensors ________________________________________________________________ 167
14.3.3 Pressure switches________________________________________________________________ 171
14.4 Relays and contactors ____________________________________________________________ 172
14.4.1 Relays _________________________________________________________________________ 173
14.4.2 Contactors______________________________________________________________________ 174
14.5 Programmable logic controllers _____________________________________________________ 175
14.5.1 Design and function of a PLC _______________________________________________________ 176
14.6 Overall layout of the signal control section____________________________________________ 176
14.7 Solenoids ______________________________________________________________________ 177
14.8 Spark arresting for solenoid valves __________________________________________________ 179

15 Workflow descriptions for processing machines and production systems__________________ 180
15.1 Function diagrams _______________________________________________________________ 180
15.1.1 Scope of the function diagram ______________________________________________________ 180
15.1.2 Displacement-step diagrams _______________________________________________________ 181
15.2 Sequence description by means of GRAFCET per EN 60848_______________________________ 182
15.2.1 The basic principle of a GRAFCET____________________________________________________ 182
15.2.2 Steps __________________________________________________________________________ 182
15.2.3 Transition condition ______________________________________________________________ 183
15.2.4 Actions_________________________________________________________________________ 184
15.2.5 Sequence selection ______________________________________________________________ 187
15.2.6 Returns and jumps _______________________________________________________________ 188
15.2.7 Structuring of GRAFCETs __________________________________________________________ 188

© Festo Didactic GmbH & Co. KG 574181 7

Contents

16 Design of circuit diagrams_________________________________________________________ 189
16.1 Hydraulic circuit diagrams _________________________________________________________ 189
16.1.1 Arrangement of circuit symbols in the hydraulic circuit diagram___________________________ 189
16.1.2 Position of cylinders and directional control valves _____________________________________ 191
16.1.3 Identification key for components ___________________________________________________ 191
16.1.4 Technical information _____________________________________________________________ 193
16.2 Electrical circuit diagram __________________________________________________________ 194
16.2.1 Electrical circuit diagram of an electro-hydraulic control system___________________________ 195
16.2.2 Identification of components _______________________________________________________ 196
16.2.3 Logic element tables for relays and contactors_________________________________________ 197
16.2.4 Actuated contacts and sensors _____________________________________________________ 198
16.3 Terminal connection diagram_______________________________________________________ 198
16.3.1 Structure of a terminal connection diagram ___________________________________________ 201
16.3.2 Wiring for an electro-hydraulic control system _________________________________________ 203

17 Safety measures for electro-hydraulic control systems _________________________________ 204
17.1 Hazards and protective measures ___________________________________________________ 204
17.2 Effects of electric current on the human body__________________________________________ 205
17.2.1 Effects of electric current __________________________________________________________ 205
17.2.2 Electrical resistance of the human body ______________________________________________ 206
17.2.3 Variables influencing the risk of accident _____________________________________________ 207
17.3 Protective measures against accidents with electric current ______________________________ 208
17.3.1 Protection against direct contact ____________________________________________________ 208
17.3.2 Earthing ________________________________________________________________________ 208
17.3.3 Protective extra-low voltage _______________________________________________________ 208
17.4 Control panel and indicators _______________________________________________________ 209
17.4.1 Mains switch ____________________________________________________________________ 209
17.4.2 Emergency stop _________________________________________________________________ 209
17.4.3 Control elements for an electro-hydraulic control systems _______________________________ 210
17.5 Protecting electrical equipment against environment influences __________________________ 212
17.5.1 Identification of the degree of protection _____________________________________________ 213
17.6 Safety principles for electro-hydraulic systems ________________________________________ 214
17.6.1 Layout of an electro-hydraulic system________________________________________________ 214
17.6.2 Commissioning an electro-hydraulic system___________________________________________ 215
17.6.3 Repair and maintenance of an electro-hydraulic system _________________________________ 215

8 © Festo Didactic GmbH & Co. KG 574181

Contents

18 Circuit symbols__________________________________________________________________ 216
18.1 Circuit symbols for hydraulic components ____________________________________________ 216
18.1.1 Circuit symbols for hydro pumps and hydraulic motors __________________________________ 216
18.1.2 Circuit symbols for valves__________________________________________________________ 217
18.1.3 Circuit symbols for directional control valves __________________________________________ 217
18.1.4 Circuit symbols for actuation methods _______________________________________________ 219
18.1.5 Circuit symbols for pressure regulators ______________________________________________ 220
18.1.6 Circuit symbols for flow control valves _______________________________________________ 220
18.1.7 Circuit symbols for shut-off valves___________________________________________________ 221
18.1.8 Circuit symbols for cylinders _______________________________________________________ 221
18.1.9 Circuit symbols for other components________________________________________________ 222
18.1.10 Measuring devices _______________________________________________________________ 223
18.2 Circuit symbols for electrical components ____________________________________________ 223
18.2.1 Circuit symbols for basic functions __________________________________________________ 223
18.2.2 Circuit symbols for electromechanical drives __________________________________________ 225
18.2.3 Circuit symbols for relays and contactors _____________________________________________ 226
18.2.4 Circuit symbols for sensors ________________________________________________________ 226

Standards_____________________________________________________________________________ 227

Index_________________________________________________________________________________ 228

© Festo Didactic GmbH & Co. KG 574181 9

Preface

Hydraulics is the study of the flow characteristics of fluids. This manual places emphasis on the generation
of forces and motion with the help of fluids. Hydraulic fluid is the transmission medium in the field of
hydraulics.
Hydraulics and electro-hydraulics are successfully used in many areas of industrial automation. For
example, woodworking machines, machine tools, processing systems, presses, plastics processing
machines and conveyor systems are operated all over the world with electro-hydraulic control systems.
Electro-hydraulic control systems are used for many applications in the field of mobile hydraulics as well, for
instance in farm vehicles, road construction vehicles and municipal vehicles.
As an introduction to this subject matter, this manual first of all examines the design and function of the
components which are used to set up hydraulic and electro-hydraulic control systems. The following
chapters describe operating sequences, the layout of circuit diagrams and safety measures.
Changing requirements and technical developments have dramatically altered the appearance of control
systems. The keywords “bus networking” and “proportional hydraulics” are mentioned here to mention just
two examples. Close-knit interaction of fluid engineering with microelectronics, sensor technology and
information technology results in numerous innovations in the field of oil-hydraulic drives and control
systems.
We invite readers of this manual to send us tips, feedback and suggestions for improvement.
Please send your comments and suggestions to [email protected],
or to Festo Didactic GmbH & Co. KG, P.O. Box 10 07 10, D-73707 Esslingen, Germany.

The authors

10 © Festo Didactic GmbH & Co. KG 574181

1 The functions of a hydraulic system

1.1 Hydraulics – what does it mean?
Hydraulic systems are used in modern production facilities and manufacturing equipment.

Hydraulics is understood as the generation of force and motion with the help of hydraulic fluid. The
hydraulic fluid is the energy transmission medium.

The importance of hydraulics in automation technology is a reflection of its diverse range of applications.
Basically, we differentiate between:
 Stationary hydraulics
 Mobile hydraulics

As opposed to stationary hydraulics, which is permanently installed at a given location, mobile hydraulics
travels on wheels or treads. One of the characteristic features of mobile hydraulics is that the valves are
frequently directly actuated by hand. In contrast, solenoid valves are used primarily for stationary
hydraulics.

Hydraulics are also used in shipbuilding, mining and aviation technology. Aviation hydraulics plays a special
role, because safety is of utmost important in this area. In order to illustrate the various functions which can
be fulfilled by hydraulics, a number of typical applications are included as examples in the following pages.

1.2 Stationary hydraulics

The following fields of application are significant in the area of stationary hydraulics:

• Manufacturing and assembly machines • Injection moulding machines

• Transfer lines • Mill trains

• Hoists and conveyors • Lifts

• Presses

A typical area of application is machine tool manufacturing.

© Festo Didactic GmbH & Co. KG 574181 11

1 The functions of a hydraulic system

Figure 1.1: Lathe, press with overhead tank

Tools and workpieces are hydraulically clamped in modern CNC machine tools. Feed units and spindle drives
may also be designed with hydraulic technology.
1.3 Mobile hydraulics
Fields of application for mobile hydraulics include:
 Construction machines
 Dump trucks, gripper arms, loading platforms
 Hoists and conveyors
 Farm machinery
Hydraulics is used for many applications in the field of construction machinery. In the case of the excavator,
for example, travelling motion, as well as all working motion such as lifting, gripping, swivelling etc., is
powered by means of hydraulics.
Working motion which is executed in straight lines is generated by linear drives (cylinders), and rotary
motion is executed by means of rotary drives (motors, semi-rotary drives).

12 © Festo Didactic GmbH & Co. KG 574181

1 The functions of a hydraulic system

Figure 1.2: Mobile hydraulics, excavator

1.4 Attributes of hydraulics

Advantages of hydraulics Disadvantage of hydraulics

Transmission of great forces through the use of small Environmental contamination due to oil leaks (fire hazard, danger
components, i.e. high power density of accident)
Accurate positioning Susceptible to contamination
Start-up from standstill under maximum load Danger due to high pressure (cutting jet)
Gentle work and reversing Temperature sensitive (viscosity changes)
Good controllability and adjustability Unfavourable degree of efficiency
Favourable heat dissipation
Uniform, load-independent motion, because fluids are hardly
compressible at all

Table 1.1: Hydraulics – advantages and disadvantages

There are other technologies in addition to hydraulics, by means of which forces, motion and signals can be

generated in the field of control technology:

 Mechanical  Electrical  Pneumatic

© Festo Didactic GmbH & Co. KG 574181 13

1 The functions of a hydraulic system

The fact that each technology has its own preferred range of applications must be taken into consideration.
A comparison of typical data for the three most widely used technologies – electrical, pneumatic and
hydraulic – is provided in Table 1.2.

Electrical Hydraulic Pneumatic

Leakage — Contamination No disadvantages except loss
Environmental influences
of energy
Energy storage
Energy transmission Danger of explosion in certain Susceptible to temperature Explosion-proof, temperature
Operating speed area, temperature sensitive fluctuation, fire hazard in the sensitive
Energy costs event of leakage
Linear motion
Difficult, only in small Limited, with the help of gases Lightweight
Rotary motion quantities with batteries
Positioning accuracy
Unlimited, with loss of energy Up to 100 m Up to 1000 m
Rigidity flow velocity v = 2 to 6 m/s flow velocity v = 20 to 40 m/s

Forces — v = 0.5 m/s v = 1.5 m/s

Minimal High Very high

Difficult and expensive, small Easily accomplished with Easily accomplished with
forces, speed can only be cylinders, good controllability cylinders, limited forces, speed
controlled at great expense of speed, very high forces is very load-dependent

Easy and powerful Easy, high torque values, low Easy, not very powerful, high
rotational speeds rotational speeds

Accuracies of down to Depending on how much is Accuracies of down to ±0.1 mm
±0.05 mm and better can be invested, accuracies of down to are possible without load
achieved ±0.05 mm and better can be reversals
achieved

Very good values can be Good because oil can hardly be Poor because air is
achieved thanks to
intermediate mechanical compressed at all compressible
elements

Not overload-proof, poor Overload-proof, very high Overload-proof, force limited by
degree of efficiency due to forces can be generated with compressed air and cylinder
downstream mechanical high system pressures of up to diameter
elements, very high forces can 600 bar (F < 30 kN to 6 bar)
be achieved (F < 3000 kN)

Table 1.2: Comparison, electrical – hydraulic – pneumatic

14 © Festo Didactic GmbH & Co. KG 574181