KNOWLEDGE IN DETAIL

Hydraulics
Basic Principles

Knowledge in Detail

Hydraulics – Basic Principles

Imprint

Knowledge in Detail

Hydraulics – Basic Principles
Publisher:
Bosch Rexroth AG
Bosch Rexroth Academy
Unterduerrbacher Straße 1097080 Wuerzburg, Germany

We do not assume any liability for the conformity of the content with the respectively applicable legal
regulations.
Subject to change.

Edition 1 (2022)
Material number: R901566373
ISBN: 978-3-9820731-5-6

The data specified only serves as a product description.
Due to the continuous further development of our products, no statement regarding a certain property
or suitability for a certain purpose can be derived from our specifications. The information given does
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© All rights reserved by Bosch Rexroth AG, also in case of application of property rights. We reserve all rights for disposition
including copyrights and distribution rights.

3

Advanced training with the Bosch Rexroth Academy

Bosch Rexroth AG has established itself as a competent partner for basic and advanced trainingof numerous business and institutions.
The portfolio of the Bosch Rexroth Academy as central department for advanced training ofBosch Rexroth AG includes customized offers for various technologies including hydraulics,
pneumatics or mechatronics for any educational needs.
The educational offer of the Bosch Rexroth Academy include:▶ Training
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4Table of contents

5

Table of contents
Imprint2

3 Components of hydraulic systems

59

Advanced training with the Bosch Rexroth Academy 3

3.1.	Pressure medium, displacement,characteristic curves

59

3.1.1	Hydraulic fluids in comparison

59

Table of contents

5

1 General information

9

1.1	Introduction to hydraulics

9

1.1.1 Definition

3.1.2	Displacement principle and its application 61

9

3.1.3	Characteristic curves and characteristic
zones of pumps and motors

67

1.1.2 Historical development

9

3.2 Hydraulic pumps

75

1.1.3	Fields of application of hydraulics

10

3.2.1 External gear pumps

75

1.2 Drive technologies in comparison

13

3.2.2

Internal gear pumps

81

1.2.1 Drive technologies

13

3.2.3

Vane pumps

83

1.2.2	Comparison of drive technologies

14

3.2.4	Axial piston pumps – swash plate design89

1.2.3	Differences in energy supply and conversion 15

3.2.5	Axial piston pumps – bent axis design94

1.2.4	Differences in energy distribution

15

3.2.6	Radial piston pumps with internal support 99

1.2.5	Properties of the transmission medium

16

3.2.7	Radial piston pumps with external support102

1.2.6	Properties of drive technologies17

3.2.8	Annular gear pumps

104

1.2.7 Conclusion

18

3.2.9	Screw pumps

106

1.3 Graphic symbols

18

3.2.10	Pump regulating systems

109

1.3.1 Purpose18

3.2.11	Hydraulic pumps in comparison

121

3.3 Hydraulic valves125

3.3.1	Overview of hydraulic valves125

3.3.2	Operation of hydraulic valves

133

3.3.3

Directional control valves

136

1.3.2	Graphic symbols according to DIN ISO 1219 18
1.3.3	Graphic symbols according to
DIN ISO 1219 – Pumps, motors,
cylinders, accessories

19

1.3.4	Graphic symbols according to
DIN ISO 1219 – Hydraulic valves22

3.3.4	Operating behavior of directional
control valves

143

2 Basic principles of physics

25

3.3.5

Pressure relief valves

148

2.1	Basic principles of hydraulics

25

3.3.6

Pressure reducing valves

156

2.1.1	Hydrostatics – Pascal's Law

25

3.3.7

Pressure sequence valves

162

2.1.2	Hydrodynamics - Bernoulli's Principle

30

3.3.8

Pressure cut-off valves

168

2.1.3	Viscosity of fluids

31

3.3.9

Non-return valves

172

2.1.4	Orifices in hydraulic lines

35

2.1.5 Pipe flows

37

2.1.6	Compressibility of fluids

40

2.1.7 Cavitation

42

2.2	Basic principles of mechanics

46

2.2.1	Path, velocity and acceleration

46

2.2.2	Force and torque48

2.2.3	Energy and work

52

2.2.4

Performance

54

2.2.5

Efficiency

55

2.2.6	Connection between hydraulic andmechanical quantities

57

3.3.10	Pilot-operated non-return valves

175

3.3.11	Throttle valves

180

3.3.12	Flow control valves

185

3.4 Hydraulic cylinders

191

3.4.1	Basic principles of hydraulic cylinders

191

3.4.2

Ram type cylinder

199

3.4.3

Telescopic cylinders

201

3.4.4

Differential cylinders

205

3.4.5

Servo cylinders

209

3.4.6

Double-acting cylinders

213

6

Table of contents

3.5 Hydraulic motors

217

4.3 Hydrostatic drives

3.5.1 External gear motors

217

3.5.2

Internal gear motors

221

4.3.1	Hydrostatic operating principles incomparison316

3.5.3

Vane motors

224

3.5.4	Axial piston motors - swash plate design 228
3.5.5	Axial piston motors - bent axis design

232

3.5.6	Radial piston motors with internal support 237
3.5.7	Radial piston motors with external support 241
3.5.8	Annular gear motors – Gerotor principle 244

316

4.3.2

" Predefined flow" operating principle

322

4.3.3

" Predefined pressure" operating principle 329

4.3.4" Predefined pressure difference"
operating principle

334

4.3.5

"Predefined speed" operating principle

335

4.3.6

" Predefined power" operating principle

338

3.5.9	Annular gear motors – Orbit principle

246

4.4	Pressure and force-depending
control systems

339

3.5.10	Hydraulic motors in comparison

250

4.4.1	Pressure limitation in hydraulic systems

339

3.6	Connection technologies251

4.4.2	Control system with pressure switch

342

3.6.1	Connection technologies in comparison251

3.6.2	Pipe and hose lines

254

4.4.3	Control of actuators with low
operating pressure

346

3.6.3	Vertical stacking260

3.6.4	Manifolds

262

3.6.5	Control blocks

264

3.7 Accessories267

3.7.1 Hydraulic accumulators

267

3.7.2

Hydraulic filters

277

3.7.3

Coolers

281

3.7.4

Manometers

286

3.7.5

Pressure switches

290

3.7.6

Pressure transducer

293

3.7.7	Digital pressure indicators

294

3.7.8	Filling level measurement

4.4.4	Control of actuators in parallel operation 348
4.4.5	Circuits with hydraulic accumulators

353

5 Hydraulic power units and systems 359
5.1	Hydraulic drive units359

5.1.1	Drive units in hydraulics

359

5.1.2	Design of a hydraulic power unit

360

5.1.3	Modular standard power units364

5.1.4	Modular standard small power units365

5.1.5	Smart connected supply systems

366

5.1.6	Modular large power units

366

294

5.1.7	Low-noise compact power units –Silent power units367

3.7.9	Flow measurement

295

5.1.8 Individual power units368

3.7.10	Temperature measurement ofhydraulic fluids

296

5.1.9 Drive modules 

368

5.1.10 Clamping and drive modules

369

4 Basic circuits of hydraulics

297

5.1.11 Compact modules

370

4.1	Circuit diagrams in hydraulics

297

5.1.12 Drive units370

5.1.13 Hydraulic power units in comparison371

4.1.1	Graphical illustration of hydraulic circuits 297

4.2	Open and closed-loop control
with valves

300

4.2.1	Open-loop control with directional
control valves

300

4.2.2	Velocity control with throttle valves

304

4.2.3	Load-independent velocity control withflow control valves

309

4.2.4

312

Rapid traverse circuits

5.2	Variable speed pump drives (Sytronix)372
5.3	Training systems in hydraulics(training power units)

374

Index377

7

8

Chapter 1: General information

9

1 General information
1.1	Introduction to hydraulics
1.1.1 Definition

1.1.2 Historical development

Hydraulics is the science of resting and flowing
fluids. In technical practice, hydraulics is generally
understood as the generation of forces and motion by
hydraulic fluids. The term is derived from the ancient
Greek words "hydor" (water) and "aulos" (pipe).

As far back as the ancient world people were utilizing
the energy of flowing water. For example, there isevidence to suggest that the first water wheels werebuilt around 300 B.C. They are still being used today inwatermills and their technical advancement can still beseen in the water turbines of power stations.

as of approx. 5000 B.C.

People utilize the energy of flowing water.

approx. 300 B.C.

The first water wheels are created and represent a milestone in thetechnological history of mankind.

as of approx. 1600

Water pressure is used as drive power.

1653

French physicist Pascal (1623-1662) illustrates the hydrostatic principle
using the hydraulic press as an example.

1795

British engineer Joseph Bramah (1749-1814) produces a hydraulic press
using water as a hydraulic fluid for generating large forces. He is thus
considered to be the developer of industrial applications in hydraulics.

1851

British industrialist William G. Armstrong (1810-1900) develops anaccumulator ("weight accumulator") with which large flows can be generated.

1905

Beginning of oil hydraulics: Williams and Janney use mineral oil asa transmission medium for hydrostatic transmissions for the first time.

1922

The engineer Hans Thoma invents the radial piston pump and develops it
further for industrial use. The technical field of industrial hydraulics develops
and becomes increasingly important.

as of approx. 1950

Oil hydraulics becomes prevalent in all areas of industrial hydraulics.
The first servo valves for industrial hydraulics come into use Proportional
control valves with analog electrical control are developed on constructive
basis of on/off valves and introduced to industrial applications.

as of approx. 1980

Introduction of digital electronics in continuous control valve technology andassociated with the development of digital control technology.

as of approx. 2015

With "Industry 4.0", comprehensive digitalization and networking ofcomponents and functional sequences as well as complete linking withadjacent technology areas are also making their way into hydraulics.

Overview of the history of hydraulics

10

Chapter 1: General information

1.1.3	Fields of application of
hydraulics
Hydraulic systems are used in the fields of powertransmission and in both open and closed-loop
control technology. In order to classify the varietyof possible fields of application, a distinction is
generally made between industrial hydraulics(or stationary hydraulics) and mobile hydraulics.

Applications in industrial
hydraulics
The term industrial hydraulics comprises applications
in which hydraulic components are used in fixedinstallations. Examples include machine tools,
plastics processing machines, presses and applicationsin the rolling mill industry.

Plastic injection molding machine

Hydraulic axis

Processing machine for cardboard

Blank cutting line in the automotive industry

Chapter 1: General information

Tower Bridge in London

Deep-sea winch

Lock in the Panama Canal

Offshore wind farm

Tunnel boring machineFrancis turbine

11

12

Chapter 1: General information

Applications in mobile hydraulics
Mobile hydraulics comprises applications in which
hydraulic components are installed in mobile machines.
For example, here hydraulics is used in hydraulicexcavators, wheel loaders, road rollers, snow groomers,
tractors, lift trucks, or municipal vehicles.

Mobile excavator

Tractor with hoist

Snow groomer

Caterpillar crane

Truck mounted heavy duty crane

Wheel loader

Chapter 1: General information

13

1.2 Drive technologies in comparison
1.2.1 Drive technologies
Solutions from the technological fields of hydraulics,
pneumatics, electrics and mechanics come into use
when designing drives:▶ In hydraulic drives, motion is generated by means ofhydraulic fluid. Hydraulic drives are used in manyindustrial fields as well as in mobile machines suchas in excavators.
▶ In pneumatic drives, motion is generated by meansof compressed air. Well-established applications
include pneumatic assembly tools for screws andnuts in vehicle garages and the transportation oflightweight goods on production lines.
▶ Electric drive technology works mostly withelectric motors, which are being increasingly
controlled electronically. Electric drives are used,
for example, in high-precision machine tools or inprinting presses.
▶ Mechanical drives can generate translational orrotatory motion or curves by means of either crankdrives, transmissions with a fixed transmission ratio,
stepless transmissions or cam gears.

Different requirements are placed on drive technology,
depending on application and use.
Differences between the drive technologies arisein particular with regard to the energy supply,
the distribution of the energy, the properties of thetransmission medium used and the properties of thedrive (type of motion) itself.
In most applications in industry and other technicalfields, several drive technologies are represented andwork in interaction. This allows the advantages of eachtechnology to be exploited and their disadvantages tobe offset in the overall system design.

Interaction of different drive technologies in modern stage technology (Krakow Opera)

14

Chapter 1: General information

1.2.2 Comparison of drive
technologies
The following table contains a comparison of drive
technologies according to their most important
technical criteria.
Criterion

Hydraulics

Pneumatics

Electrics

Mechanics

Energy carrier

Hydraulic fluid

Air

Electrons

Motion, position,
deformation

Energy transmission

Pipes, hoses,
bores

Pipes, hoses,
boresElectrically conductive
material

Shafts, rods, belts,
chains, wheels etc.

Conversion from /into mechanicalenergyHydraulic pump,hydraulic motor,
hydraulic cylinderCompressor,
pneumatic cylinder,
pneumatic motor

Generator, magnet,
electric motor—

Most importantcharacteristics

Pressure p,
flow qV

Pressure p,
flow qV

Voltage U,
electric current I

Force F,
Torque M,
Velocity v,
Speed nStorage

Bladder-type
Compressed air
accumulator, piston-type reservoir
accumulator, diaphragmtype accumulator

Capacitor, battery,accumulator

WeightPower density

Very good(high working
pressures)Good(limited by max.
working pressure)Not very good(power-weight ratioof electric motors
approx. 10 times
higher than that ofhydraulic motors)Good(if energy conversion
is not necessary;
limitations if highdemands are placed oncontrollability)

Efficiency

Dependent on leakage
and friction during
energy conversion;
losses during valve
control (open andclosed loop)

Dependent on leakage
and friction during
energy conversion;
losses during valve
control (open andclosed loop)

Dependent on
availability of electricity
as primary energy
sourceDependent on size offrictional losses

Generation of linear
motionVery easy(by means of cylinders;start-up and reversalof motion at full load
possible)

Very easy(by means of cylinders)Not very easy
(by means of linear
electric motor,
threaded spindle etc.)

Simple(via crank drive,
spindle etc.)

Generation ofrotational motion

Easy(by means ofhydraulic motor)

Easy(by means ofcompressed air motor)

Very easy(by means rotaryelectric motor)

Very easy(by means oftransmission)

Generation of curves

Not very goodNot very goodNot very good

Very good forcertain applications(bending technology)

Path accuracy

Very good(fluid is hardy
compressible)

Not very good(air is compressible)

Varies:(not very good with
asynchronous motors
very good withsynchronous andstepping motors)

Very good(by means of form andforce fit)

Very good(by means of switches,
relays, semiconductors,
variable speed motors,
variable resistors etc.)

Good(by means oftransmissions,lever systems etc.)

Controllability
Very good
Very good(open and closed loop), (by means of valves and (by means of valves)signal processing
variable displacement
pumps; use of servo
valves in control
technology;
further improvementsby combining withelectric systems)
Technical criteria of various drive technologies

Chapter 1: General information

15

1.2.3	Differences in energy
supply and conversion
The following overview illustrates the various
methods and components for energy supply andenergy conversion of drive technologies, divided into
stationary and mobile applications.
Drive
technology

Operation Energy supply Energy conversion

Hydraulics

stationary Mains

mobilePneumatics

Electrics

Mechanics

Fuel

Electric motor and compressor

Fuel

Fuel

Generator, combustion engine

Fuel cell--

Accumulator

--

Fuel

Pneumatic motor,
pneumatic cylinder--

stationary Mains andelectric motor
mobilePneumatic valve

Combustion engine
and compressor ordiesel-electric drive1)
and compressor

stationary Mains
mobileGeneration of motion

Electric motor + hydraulic pump Hydraulic valve,
Hydraulic motor,
variable displacement
hydraulic cylinder
pumps, variable-speed
pump drives or variable
Combustion engine
displacement motors,
and hydraulic pump or
meter-out control
diesel-electric drive1)
and hydraulic pumpstationary Mains
mobileControl

Transmission or speed
adjustment
Combustion engine

Converter,
switch,relay ...

Steplessly adjustabletransmission (by meansof centrifugal force orlever ...)

Electric motor

Crank drives,transmission with
fixed or steplesstransmission ratio,
cam gears1) ... diesel-electric drive consisting of diesel engine, generator and electric motor

Energy supply and energy conversion of drive technologies

1.2.4	Differences in energy
distribution
Depending on the drive technology and thetransmission medium used, energy distribution isdetermined using the following criteria:▶ Range of energy transmission▶ Flow velocity of the medium▶ Propagation rate of waves in the medium

An economically viable energy transmission distanceis limited by transmission losses which depend on theflow of the medium.

Drive
technology

Transmission medium

Range of energy
transmission

Flow velocity

Wave propagation
velocity

Hydraulics

Hydraulic fluid< 100 m2 to 15 m/s

Approx. 1.5 - 2 km/s

Pneumatics

Compressed air< 1000 m

10 to 50 m/s

Approx. 0.34 km/s

Electrics

Electric charge< 1000 km

0.0007 m/s (electron velocity)

Approx. 300,000 km/s
(in vacuum)

Mechanics

Mechanicalcomponents

Limited bymechanical stiffness----

Transmission characteristics of drive technologies

16

Chapter 1: General information

1.2.5	Properties of thetransmission medium
Hydraulic fluid, compressed air, electric charge andmechanical components are transmission media
whose properties influence the possibilities of energy
storage, velocity of energy removal and environmental
compatibility of the relevant drive technology.

Energy storage
Depending on the different drive technologies,
energy is stored in different ways:▶ Hydraulics
In hydraulics, the energy storage effect is minimal
due to the low compressibility of the hydraulic fluidwhen compared with the compressibility of gases.
Energy is stored using gas, usually nitrogen,as a compression medium. Due to the high systempressure, high amounts of energy are stored.
This requires special safety-related measures.
▶ Pneumatics
Air is used as a compression medium to store
pneumatic energy. Besides special pressure vessels,
the entire system constitutes an energy store.
For safety reasons, the system pressure must
therefore be kept relatively low. The pressure range
in pneumatic systems lies between 4 and 6 bar.
▶ Electrics
Electric energy storage is associated with highenergy losses. As a general rule, coils and capacitors
are suitable storage media. With capacitors,
the energy loss can, however, be controlled moreeasily than with coils. Apart from capacitors,
batteries and accumulators in particular are used
to store energy in electric drive technologies.
▶ Mechanics
Mechanical energy is stored by means of spindle
drives (potential energy) and braking energy bymeans of flywheels (kinetic energy). This enables
connecting of energy during acceleration processes.
Limited amounts of energy can be stored throughthe use of engineered springs.

Velocity of energy removal
Energy stored in hydraulic, pneumatic and mechanicalaccumulators can be retrieved very quickly.
Capacitors can also quickly release energy.
Batteries and accumulators can store considerably
more energy, though they only release it slowly.

Environmental compatibility
The drive technologies differ considerably interms of their environmental compatibility due
to the transmission medium used in each case(hydraulic fluid, compressed air, electrical charge, ...):▶ Hydraulics
In hydraulic drives, undesired leakage of hydraulicfluids from the system (external leakage)
constitutes a potential hazard for the environment.
This hazard can be largely excluded by using
biodegradable fluids or water. Collection of leaked
fluids and proper disposal of used hydraulic fluids
must be ensured.
▶ Pneumatics
Pneumatic drives in modern systems (oil-free air)are very environmentally compatible, as compressed
air can be directly discharged into the environment
without filtration. Return of the transmission
medium to a tank, as is the case withhydraulic drives, is not necessary here.
▶ Electrics
In electric drives, electro-magnetic radiation must
be taken into account and suitable countermeasures
may need to be taken.
▶ Mechanics
Mechanical drives are very environmentally friendly
in fault-free operation as there is no impact on theenvironment (no exhaust air or external leakage ofcomponents).

Chapter 1: General information

1.2.6 Properties of drive
technologies
Drive technologies differ in the conditions
required and options available to generatemotion. Criteria for comparison preferably
include motion type (rotary, linear), structuraldesign (direct drive, used in transmission),force density, control behavior, accuracy,efficiency and safety aspects.
The following findings are based on the comparison of
application characteristics of drive technologies:▶ Hydraulic and pneumatic drives are particularly
suitable for linear and rotatory motion that can beeasily generated by hydraulic cylinders or motors.
Electric drives have a complex structure and are
predominantly built to generate rotational motion.
Depending on their design, mechanical drives are
suitable for both linear and rotary motion as well as
for producing predefined curves.
▶ In comparison to electric drives, the volume-related
power density of hydraulic drives is much larger.
In contrast, the power density of pneumatic drives
is significantly lower.
▶ Hydraulic and pneumatic drives are used bothas direct drives as well as with mechanicaltransmissions. Electric drives often use
a transmission to adjust torque and speed.
With electric drives, integration of the motor into
the machine construction is only economicallyefficient if the highest demands are placed on
dynamics and stiffness.
▶ The achievable torques and forces of hydraulic andelectric drives are considerably larger than those inpneumatics. For generation of identical forces,
electric drives need to be considerably larger thanhydraulic drives.

17▶ Electric motors need about three times the rated
current to generate torque from standstill.
This results in considerable heating of the electricmotor, making additional cooling necessary.
▶ Electric and mechanical drives offer a high degreeof efficiency. The efficiency of hydraulic andpneumatic drives is lower as there are additional
losses due to flow losses and leakage. Moreover,in pneumatics, efficiency is considerably reduced by
the heat generated in the compressor that isdissipated into the environment.
▶ In hydraulic and pneumatic drives, overload
protection can be easily achieved by means ofoverload safety valves (pressure relief valves).
In mechanical drives overload protection can also
be achieved without any problem by predetermined
breaking points. In electric drives, overload
protection is more complicated, as it is difficult todissipate resulting losses in the form of heat.
▶ By using isolation valves in hydraulic and pneumatic
drives, it is easy to stop motion in case of emergency.
Electric drives offer a quick emergency stop by
disconnecting the energy supply. Additional braking
measures should be provided to prevent the electricmotor continuing to run uncontrolled.
▶ Pneumatic drives can be used in explosive areas
with relatively low effort, provided the air does notcontain any oil. In hydraulic systems, the use offlame-resistant hydraulic fluids is essential.
When using electrically controlled valves,the components must be designed in a way which is
intrinsically safe or explosion-proof. Electric drives,
however, must always be encapsulated inpressure-tight housings. In mechanical drives,
suitable materials must be used. For instance,
use of aluminum is prohibited in mining operations(applies to all drive technologies).

18

Chapter 1: General information

1.2.7 Conclusion

1.3 Graphic symbols

Comparison of individual drive technologies leads tothe following conclusions:▶ Hydraulics
Hydraulic drives offer the advantage of generatinghigh forces yet with a very compact design.
A disadvantage of this drive technology is theeffort required to prevent hydraulic fluid fromescaping and entering the environment.
▶ Pneumatics
Pneumatic drives can generally be used if fast motion
and little force are required. Further advantages
include comparatively low capital costs and goodenvironmental compatibility. The relatively high noise
development is a disadvantage of this technology.
▶ Electrics
Electric drives feature high control dynamics andflexibility. On the other hand, capital costs arecomparatively high.
▶ Mechanics
Mechanical drives are straightforward to construct
and are easily able to generate linear and rotationalmotion. However, one disadvantage is the lesseffective controllability.
By combining various drive technologies,
e.g. the combination of hydraulics and electricalengineering in variable-speed pump drives (Sytronix),
the advantages of the respective technology can be
optimally utilized and the disadvantages compensatedas required.

1.3.1 Purpose
In hydraulics, graphical symbols (also referred to as
switching symbols) are used for the abstract illustrationof fluid power components and their functions,as well as to explain hydraulic circuit systems.
Graphic symbols consist of one or more basic
element(s) and generally of one or more functional
symbol(s) in accordance with a specific system.
They are designed in such a way that the function of
the components or circuits illustrated can be quickly
and easily understood.
Structural details of components are not taken into
account in the symbolic illustration.
Graphic symbols are mainly used in circuit diagrams,
product catalogs and operating instructions.
They are an important aid in project planning,assembly, commissioning, inspection, troubleshooting
and maintenance of hydraulic systems.

1.3.2	Graphic symbols
according to DIN ISO 1219
Scope and standard
Graphic symbols for fluid technology are usedworldwide and are defined in DIN ISO 1219 andstandardized in an internationally binding manner.
The exclusive sale of standard sheets in Germany iscarried out by:▶ Beuth Verlag GmbH, 10772 Berlin
The following list shows examples of graphic
symbols according to the standard DIN ISO 1219
(Part1: "Graphic symbols for conventional use anddata-processing applications"). This list serves asworking aid for assignment of graphic symbols andreading or creating of hydraulic circuit diagrams.

Chapter 1: General information

1.3.3	Graphic symbols according to DIN ISO 1219 –Pumps, motors, cylinders, accessories
Element description

SymbolElement description

Energy source, hydraulic

Energy source, pneumatic

Drive unit
(except for electric motor)

Electric motor

Main line (rigid)
Control or leakage oil line

Hose line (flexible)

Line crossing(lines not connected)

Line connection

Tank

Tank with line

Quick-release coupling
without non-return valve tobe opened mechanically,
coupled/uncoupled

Quick-release couplingwith non-return valve tobe opened mechanically,
coupled/uncoupled

Hydraulic pump, general

Hydraulic motor, general

Fixed displacement pump with:• 1 flow direction• 1 direction of rotation

Fixed displacement
pump/motor with:• 1 flow direction• 1 direction of rotation

Variable displacement
pump with:• 2 flow directions• 1 direction of rotation• drain port

Fixed displacement
motor with:• 2 flow directions• 2 directions of rotation

Variable displacement
pump with hydraulic servo
adjustment and:• 1 flow direction• 1 direction of rotation• drain port

Variable displacement
pump/motor with:• 2 flow directions• 2 directions of rotation• drain port

Symbol19

20

Chapter 1: General information

Element description

SymbolElement description

Variable displacement pumpwith pressure controller(pilot-operated) and:• 1 direction of rotation• drain port

Variable displacement pumpwith combined pressure/flow
controller and:• 1 direction of rotation• drain port

Hydraulic swivel motor

Compact hydro transmission

Single-acting hydrauliccylinder, with piston rod on
one side, return stroke byspring force, spring chamberwith port

Double-acting hydrauliccylinder with piston rod on
one side

Single-acting telescopic
hydraulic cylinder

Double-acting telescopic
hydraulic cylinder

Filters, general

Breathing filter tank

Separator

Filter with separator

Filter with bypass valve

Filter with visual
clogging indicator(pressure difference-based)

Accumulator, general

Piston-type accumulator

Bladder-type accumulator

Diaphragm-type accumulator

SymbolChapter 1: General information

Element description

SymbolElement description

HeaterCooler with cooling fluid

Thermostat

Pressure sensor,
output signal analog

SymbolP
Pressure measuring instrument(manometer)

Pressure differential gauge

Fluid level indicator(sight glass)

Thermometer

Flow indicator

Flow meter

Tachometer

Torque measuring instrument

Pressure switch,
electro-mechanical, adjustable

Pressure switch,
electronically adjustable,
output signal switchingP
Accumulator with accumulator
shut-off block
Accumulator shut-off
block with:• system-shut-off valve• pressure relief valve(safety valve)• manual relief• pressure measuring
instrument (manometer)

S

M1

P

T

M2

Selection of symbols from the fields of pumps, motors, cylinders, accumulators and accessories

21

22

Chapter 1: General information

1.3.4	Graphic symbols according to DIN ISO 1219 – Hydraulic valves
Element description

SymbolElement description

Hydraulic operation(single-stage)

Pneumatic operation(single-stage)

Hydraulic operation(two-stage)

Operation by means ofsolenoid coil with one winding

Operation by means ofsolenoid coil with twocounteracting windings

Operation by means ofsolenoid coil with twocounteracting windings,
continuously adjustable

Electrical operation(solenoid coil with one
winding), hydraulic pilot
control with external pilot
oil supply

Electrical operation(solenoid coil with twocounteracting windings,
continuously adjustable),
two-stage hydraulic pilot
control with external pilot
oil supply

Operation by pushbutton

Operation by pedal

Operation by fulcrum

Operation by lever

Operation by plunger

Operation by plunger withadjustable stroke limitation

Operation by roller plunger

Operation by spring force

Operation by hydraulicpressurization (by the useof pilot oil) or pressure
relief, directly acting on theoperating element

Operation by hydraulicpressurization (by the use ofpilot oil) or pressure relief
by means of different-sized,
opposing control areas

Two operations acting inparallelMechanical feedback

SymbolChapter 1: General information

Element description

SymbolElement description

External pilot oil line

Internal pilot oil channel

Throttle valve, adjustable

Non-return valve

Non-return valve with spring

Pilot-operated double
non-return valve with spring,valve is opened by pilotpressure

Shut-off valve

Shuttle valve (OR function)

Throttle/non-return valve,adjustable

Double non-return valve,pilot-operated

2-way flow control valve,permanently adjusted,with bypass non-return valve

3-way flow control valve,adjustable

Flow divider

Flow totalizer

Pressure control valve anddirectional control valve
installation kit, poppet design

Throttle valve, operation withroller plunger, spring returnBA

2/2 directional control valve,normally open,
solenoid operation,
spring return

2/2 proportional directional
control valve, normally closed,solenoid operation,
spring return

3/2 directional control valve,normally closed,solenoid operation,
spring return

3/2 directional poppet valve,normally closed,solenoid operation,
spring return

Symbol23

24

Chapter 1: General information

Element description

SymbolElement description

4/2 directional control valve,solenoid operation,
spring return

4/3 directional control valve,
hydraulic operation,
spring centering

4/3 directional control valve,
direct solenoid operation,
spring centering ofcenter position

4/3 directional control valve,pilot-operated, electro-hydraulicoperation, spring centering ofcenter position, external pilot
oil supply and pilot oil return

4/3 directional control valve,two-stage, electro-hydraulicoperation, pressure centeringof center position,
external pilot oil return

4/3 directional control valve,two-stage, electro-hydraulicoperation, spring centering ofcenter position, main control
spool with additional pressure
centering, with emergency
operation, external pilot
oil return

4/3 directional control valve,pilot-operated, electro-hydraulicoperation, spring centering ofcenter position, with emergency
operation, external pilot
oil return

4/3 directional control valve,pilot-operated, electricaloperation of the pilot
control stage and hydraulicoperation of the main stage,
without emergency operation,
spring centering of center
position, external pilot oil
supply and pilot oil return

4/3 proportional directional
control valve, direct solenoid
operation, spring centering ofcenter position

4/3 proportional directional
control valve, pilot-operated,with position control of mainand pilot control stages,
with integrated electronics

4/3 proportional directional
control valve, pilot-operated,with actuating solenoid, withposition control of the mainand pilot control stages, withintegrated electronics

GG

4/3-way servo valve,pilot-operated, pilot control
stage with electrical operation,with mechanical feedback of
the control spool position,with integrated electronics

Pressure relief valve,
direct-operated,internal pilot oil supply

2-way pressure reducing valve,
direct-operated, adjustable,internal pilot oil supply,
external pilot oil return

Proportional pressure relief
valve, direct-operated,solenoid acts via springon valve poppet,
internal pilot oil supply

2-way pressure reducing valve,pilot-operated,internal pilot oil supply,
external pilot oil return

Pressure relief valve,pilot-operated, internal pilot
oil supply and return

3-way pressure reducing valve,
direct-operated,internal pilot oil supply,
external pilot oil returnSelection of symbols from the field of hydraulic valves

SymbolG

G

Chapter 2: Basic principles of physics

25

2 Basic principles of physics
2.1 Basic principles of hydraulics
2.1.1 Hydrostatics –Pascal's Law

Physical measurement units of pressure
Physical unit of pressure as per definition

Short description

According to the International System of Units (SI),the physical unit of pressure is the Pascal (Pa):

Hydrostatics describe the state of resting fluids.
In this respect, Pascal's Law is of major significance.
This law of physics describes the effect of pressure
on resting fluids − the pressure propagates evenly inall directions.

Pascal's Law
Definition of pressure
Pressure is a basic physical parameter in hydrostatics.
Pressure p is defined as the vertically acting force F on
the area A.

1 Pa = 1Nm2

In hydraulics, a pressure of 1 Pa is an extremely low
and impractical value. Relevant specified pressures
could start at approx. 10000 Pa and could reach values
with up to seven digits.
Therefore, to avoid massive numerical values, the unit
megapascal (MPa) is used:

1 MPa = 106 Pa = 1
p

F
A



N
mm2

F pA
Physical unit of pressure in practiceIn hydraulics, according to the EU directive,
the unit "bar" (bar) is also permitted in addition
to the SI unit and is widely used in practice:p▶ 1 bar = 10 N/cm2▶ 1 bar = 105 Pa▶ 1 bar = 0.1 MPa
AF

In the US, however, the unit pound-force persquare inch (psi) is commonly used:▶ 1 psi = 6894.757293168 Pa

For practical reasons, the following conversion
factors are applied:
Pressure p on area A creates force F▶ 1 bar = 14.49 psi▶ 1 psi = 0.069 bar

26

Chapter 2: Basic principles of physics

Hydrostatic pressure due to gravity

With a series of vessels of different shape, it can beobserved that, provided the same fluid is used,
the pressure at the bottom will only depend on theheight of the fluid column and not on the shape ofthe vessel or the fluid quantity. This phenomenon isreferred to as a hydrostatic paradox.

If it is only gravity which acts on a fluid, then thepressure in it will depend on the height of the fluid
column and the density of the fluid. This pressure isreferred to as gravitational pressure.
In water, the increase in the hydrostatic pressure withthe height of the water column amounts to approx.
1 bar per 10 m. In air, the pressure of the earth's entire
atmosphere at sea level is approx. 1 bar.

h
p1

A

p2

p3

A
F1

A
F2

F3

p1  p2  p3F1  F2  F3Hydrostatic paradox (for the same area A)

The following relationship is derived from this:p   g  h

p
ρ
g
h

Hydrostatic pressure
Specific density of the fluid
Acceleration due to gravity(9.81 m/s2)
Height of the fluid column

The hydrostatic pressure due to gravity as described by
Pascal's Law:
The effect of a force on a resting fluid propagatesin all directions within the fluid. Without external
forces, the level of pressure in the fluid corresponds
to the weight, referred to its effective area.
The pressure always acts vertically on the tankboundary surfaces.

28

Chapter 2: Basic principles of physics

Path transmission (hydraulic lever rule)
For incompressible fluids, the following applies:
In a closed system, the total volume of the fluid does
not change.

fluid from flowing back into the hand pump and thus
prevent the working piston from lowering.
To lower the load on the lifting platform, a blocking
element is provided (here a rotary spool), which
controls the discharge of the hydraulic fluid into
the tank.

As shown in the graph "Force and path transmission"(on page 27), the volume of hydraulic fluid displacedby one piston must push against and move the otherpiston (displacement principle).
The change in partial volumes is the same in bothcylinder spaces within the system and is determinedby the following formula:

1

2

3

V  A1  s1  A2  s2The paths are inversely proportional,
as with the associated piston areas.

s1 A2
=
s2 A1
Therefore, the piston with the smaller piston area
performs a larger stroke than the piston with the larger
piston area:5

s1  s2 

A2
A1

As with mechanics, this correlation applies as thehydraulic lever rule. "Path transmission" is derived fromthis correlation.

4

1 Cylinder piston of hand pump
2 Lifting platform
3 Cylinder piston of lifting platform
4 Rotary spool
5 Non-return valves
Principle of a hydraulic lifting platform (application of force andpath transmission)

Application of force and path transmission
Force and path transmission are used, for example,
in hydraulic lifting platforms for lifting heavy loads.
The cylinder of the hand pump is characterized bya large stroke with a small piston area. This means that
only a low force is required to deliver the necessary
volume of hydraulic fluid to the working cylinder withmany strokes.
At the working piston with a larger area, there istransmission into a large force at the lifting platform
with a shorter path.
The following figure is intended to illustrate theapplication of force and path transmission toa hydraulic lift. Non-return valves prevent the hydraulicHydraulic jack(practical example of application of force and path transmission)

Chapter 2: Basic principles of physics

Pressure intensification

The flows at the primary and secondary sides behaveas the piston areas do.

The principle of pressure intensification is theconversion of an input or primary pressure toa generally higher outlet pressure or secondarypressure.
At mechanical coupling of pressurized areas, the pressure
is intensified proportionally to these areas.
The prerequisite is two firmly connected piston areas ofdifferent sizes in a closed hydraulic system.

s1

p1

s2

29

qv 1 A1=
qv 2 A2

The flow is calculated according to the following
formula.

qV 
s1 = s2

F

A1

p2

As
t

Due to the mechanical separation of the two areasof the pressure intensifier, different pressure media(e.g. hydraulic oil) can be used for the primary areaand for the secondary area (e.g. water).

A2

Hazard due to pressure intensification
Principle of pressure intensification (intensifier)Pressure p1 acts on the large piston and generates
force F that generates pressure p2 by means of thesmall piston.

p1  A1  F  p2  A2Therefore, the pressure is inversely proportional to theassociated piston areas.

p1
A
= 2
p2
A1
"Pressure intensification" is derived from this correlation.

Application of pressure intensification
A typical application example of pressure intensification
uses a component known as a pressure intensifier(see figure above "Principle of pressure intensifiers"
and section "Pressure intensifiers"on page 342).
The pressure intensifier increases an existing pressure.
The primary pressure at the input side is intensified toa higher secondary pressure at the output side at aninverse ratio of the effective piston area.

A

B

Pressure intensification in double-acting hydraulic cylinder

If the hydraulic cylinder is to be extended bypressurizing port A, but port B is closed, this would
cause a pressure intensification between the cylinderchambers (corresponding to the ratio of the areasof the piston base side and the piston rod side).
In extreme cases, this pressure increase can cause thecylinder pipe and associated components to burst.
	Notice:With regard to planning and dimensioning of
hydraulic systems, it is important to consider the
possible pressure intensification and pressure
increase by hydraulic cylinders.

Chapter 3.2: Hydraulic pumps75

3.2 Hydraulic pumps
3.2.1 External gear pumps

Disadvantages are leakage and frictional losses as wellas considerable noise development, which occur tovarying degrees depending on the design and use of
the pump.
External gear pumps consist of only a few components.
The pump housing can be manufactured from an
extruded aluminum profile with low manufacturing costs.
External gear pumps can be used in a wide speed
range and have only low requirements on the viscosityof the hydraulic fluid used. This results in numerous
possible applications, particularly in mobile hydraulics(tractors and forklifts) and industrial applications.

Short description
External gear pumps are displacement machines inwhich the displacement chambers are made up gears
with external gearing.
In the housing bores of external gear pumps, two gears
engage, one of which is driven (e.g. by means of anelectric motor). This driven gear drives the second
gear in the opposite direction. The hydraulic fluid isdelivered in the tooth clearances.

DesignCharacteristics

The figure illustrates the general design of an externalgear pump in longitudinal and cross-section.

External gear pumps are fixed displacement pumps.
They are characterized by a compact design and highpower density. They have good emergency running
properties, so that momentarily insufficient lubrication,e.g. during start-up, does not cause damage tothe pump.

1

2

3

2

4

5

5
S

6

9

8

P
6

7

1 Flange (front cover)
2 Housing
3 Bearing blocks
4 Housing cover (end cover)
5 Drive shaft with driving gear
6 Driven gear
Longitudinal and cross-section of an external gear pump

7
8
9
P
S

Bearing
Sealing surface between bearing blocks and gears
Shaft seal ring
Pressure port
Suction portChapter 3.3: Hydraulic valves125

3.3 Hydraulic valves
Classification of hydraulic valves

3.3.1 Overview ofhydraulic valves
Short description
Hydraulic valves are components for open andclosed-loop control of the energy flow in hydraulicsystems. Depending on their design, they influence
start, stop and volume of the flow, and thus also thedirection of motion, the velocity of hydraulic actuatorsand the pressure level in hydraulic systems.

The main distinction with this line of components
is made between the signal behavior and mode ofoperation of the valve:▶ On/off valves
A change in the input signal results directly in an
abrupt change of the hydraulic output signal(binary behavior; also referred to as "black andwhite valves"), without assuming an intermediate
position.
▶ Continuous control valves
A variable input signal is converted into
a continuous and proportionally adjustablehydraulic output signal. With continuous control
valves, a basic distinction is made between
proportional control and servo valves.
Further subdivision of hydraulic valves within these twomain groups is virtually identical.

Hydraulic valves

On/off valves | Continuous control valves

Pressure control
valvesDirectional
control valves

Flow control
valvesIsolation valves

Spool valves | Poppet valve
for:or as:

subplate mounting | in-line installation | block installationscrew-in cartridge valves | stack valves | sandwich valves | monoblocks
direct-operated | pilot-operated

Directional control valves:

Pressure control valves:

Flow control valves:

Isolation valves:- 2/2-design- 3/2-design- 3/3-design- 4/2-design- 4/3-design- Pressure relief valves- Pressure reducing valves- Pressure sequence valves- Pressure cut-off valves- Flow control valves- Throttle valves- Flow dividers- Non-return valves- Shut-off valves- Prefill valves- Shuttle valves- Suction valves

General criteria for classification of hydraulic valves

Chapter 3.4: Hydraulic cylinders

191

3.4 Hydraulic cylinders
3.4.1 Basic principles ofhydraulic cylinders

Characteristics

Short description
Hydraulic cylinders are components for energy
conversion that work according to the displacement
principle. They convert the flow directed into thecylinder chamber into translational, i.e. linear motion.

Use of hydraulic cylinders in a wheel loader

Hydraulic cylinders are able to transmit large
forces along a route limited by their effective length.
Depending on their construction type, hydrauliccylinders are able to transmit forces either in one or
two directions.
In relation to their frame size, hydraulic cylinders arevery powerful and are therefore used in all fields ofindustrial and mobile hydraulics.

Use of hydraulic cylinders in an extrusion press

DesignThe figure illustrates a double-acting hydraulic cylinder
in tie rod design in longitudinal section.

1

2

3

4

B

1 Piston rod
A Piston base side port
2 Cylinder head
B Piston rod side port
3 Cylinder pipe
4 Piston
5 Cylinder baseLongitudinal section of a double-acting hydraulic cylinder in tie rod design

5AChapter 3.5: Hydraulic motors

3.5 Hydraulic motors

External gear motors can be used across a wide speed
range and operated with hydraulic fluids within a large
viscosity range. This results in numerous possible
applications, particularly in mobile hydraulics andindustrial applications.
Application examples of external gear motors are as
follows:▶ Construction machines (road rollers and paving
machinery)▶ Road vehicles (buses and trucks)▶ Agriculture and forestry (combined harvesters andforestry machinery)▶ Plant construction (fan drives)

3.5.1 External gear motors
Short description
External gear motors are displacement machines inwhich the displacement chambers are made up of gears
with external gearing. High and low-pressure range are
separated by the contact of the meshing gears.

DesignCharacteristics

The figure illustrates the general design of an externalgear motor in longitudinal and cross-section.

External gear motors are fast-running fixed
displacement motors. They are characterized by
a compact design and high power density.
These motors consist of few components and arecompact in design. The housing can be manufactured
from an extruded aluminum profile with low
manufacturing costs.

1

2

3

2

4

5

5
A

6

8

B
6

L

9

217

7

1 Flange (front cover)
2 Housing
3 Bearing blocks
4 Housing cover (end cover)
5 Output shaft with gear
6 GearLongitudinal and cross-section of an external gear motor

7
8
9
A
B
L

Bearing
Sealing surface between bearing blocks and gears
Shaft seal ringHigh-pressure port
Low-pressure port
Drain portChapter 4: Basic circuits of hydraulics

297

4 Basic circuits of hydraulics
4.1 Circuit diagrams in
hydraulics
4.1.1	Graphical illustration of
hydraulic circuits
Hydraulic circuit diagrams
Circuit diagrams are created to graphically illustrate
the components and their functions, their connectionsin the hydraulic system, and their interaction in thehydraulic system.
Circuit diagrams are aids to support understanding of
the design and the description of hydraulic systems.
They are also a suitable means of avoiding ambiguities
and errors during the planning phase, production,assembly and maintenance of the hydraulic system bymeans of a standardized illustration of the hydraulicconditions.

Basic elements of hydraulic circuit diagrams
are standardized graphic symbols of hydraulics
according to ISO 1219 (see chapter "Graphic symbols"from page 18).
Graphic symbols of hydraulics do not provide
information about the design structure of thecomponents. They include abstractly represented
functional units such as drive motors, hydraulicpumps, hydraulic valves, hydraulic cylinders or
hydraulic motors, as well as accessory components
or assemblies.
The illustration of the line links shows the connections
between the individual components and assemblies.
Marking of components, compact assemblies andconnection designations facilitates the assignment of
the elements of the circuit diagram to the parts lists andconditions of the real hydraulic assembly. Furthermore,
it is possible to enter required physical characteristic
values at relevant positions of the circuit diagram.

Reading and understanding a circuit diagram as a basis for working on hydraulic systems

298

Chapter 4: Basic circuits of hydraulics

Circuit diagram/circuit schematics
The following figure illustrates the circuit diagramof a hydraulic system with supply (hydraulic pump),
components for control, safety and display as well as
the hydraulic actuator (hydraulic cylinder).

9

5

5

8

8

7

5

6
4
3

2
1

5 Manometer
1 Tank6 Pressure relief valve
2 Hydraulic pump (here fixed displacement pump)
7 Directional control valve
3 Non-return valve
8 Throttle/non-return valve
4 Return filter
9 Hydraulic cylinder
Circuit diagram of a hydraulic circuit with graphical symbols according to DIN ISO 1219

Chapter 4: Basic circuits of hydraulics

The following figure illustrates the components ofa hydraulic system in circuit schematics. These circuit
schematics were derived from the illustrated circuit
diagram. The abstract graphic symbols have been
replaced by cross sections of the components.

100
50

0

This form of illustration of a hydraulic circuit,which is mainly used in basic and advanced training,
clearly shows the design and interaction of individual
assemblies, components and parts.

150

100
50

200

9

250

5

0

150
200

250

5

8

8

A

299

B

7

100

5

50

0

6

150
200

250

3

4
2

1

5 Manometer
1 Tank6 Pressure relief valve
2 Hydraulic pump (here external gear pump)
7 Directional control valve
3 Non-return valve
8 Throttle/non-return valve
4 Return filter
9 Hydraulic cylinder
Associated circuit schematics (with cross sections) of the hydraulic circuit

300

Chapter 4: Basic circuits of hydraulics

4.2 Open and closed-loop
control with valves

The figure illustrates the circuit diagram for a cylinder
control with an electrically operated 4/3 directional
control valve in the center position.

4.2.1 Open-loop control withdirectional control valves

5

Short description
Hydraulic directional control valves are components
manipulating start, stop, and flow direction ofa hydraulic fluid. They establish line connections by
opening, blocking or changing one or more flow paths.
Depending on the application and task, different
variants of control systems with directional control
valves are realized, which differ in terms of design andfunction.

DesignA control system with directional control valvesessentially consists of the following main components:▶ A hydraulic pump delivers the flow.
▶ A directional control valve controlling start,
stop and the direction of flow.
▶ An actuator, here a hydraulic cylinder,
performs work with the aid of the flow.
▶ A pressure relief valve limits the working pressureof the system.

A

4

B
0

a
P

b
T

3

6

2

1

1 Tank4 4/3 directional control valve
2 Hydraulic pump
5 Hydraulic cylinder
3 Manometer
6 Pressure relief valve
Cylinder control with electrically operated 4/3 directional
control valve

In the symbol of a directional control valve shownin the circuit diagram, ports P and T are connectedto each other in center position (zero position).
This is also called neutral circulation, and sucha directional control valve is called an unloading valve.
The advantage is that the hydraulic pump in thisswitching position of the directional control valve saves
energy, since it only has to build up the low pressure
to overcome the valve and line resistances.

Continuous directional control valves with integrated electronics
for use in industrial hydraulics

Chapter 5: Hydraulic power units and systems359

5 Hydraulic power units and systems
5.1	Hydraulic drive units
5.1.1	Drive units in hydraulics
Short description
Hydraulic power units are independent assemblies
of components for controlled provision of hydraulicenergy. The system is driven either by an electric motor
or a combustion engine.

Requirements
Hydraulic power units must be adjusted to therequirements and specifications of different hydraulicsystems. For example, different specification profiles
result from flow requirements, working pressure,environmental conditions or transport and installation
options. Constant focus is placed on low noise leveland optimum energy efficiency.

Large hydraulic power unit (with oil-air heat exchanger)

Use of standard components and modular assemblies
in hydraulic power units ensures better handlingof the diversity of variants resulting from thevarious requirements. Thanks to a modular design,
it is possible to realize optimum structural solutions
while taking into account economic aspects andensuring a high degree of operational reliability,
low noise emissions and energy consumption as wellas ease of maintenance and high durability.

Fields of application
Typical application cases for hydraulic power units
are stationary applications in general mechanicalengineering (structural and hydraulic engineering,
metallurgy), in the plastic-processing industry,in lifting and elevation units and in presses.
Small power units with electric motors are usedin mobile hydraulics, for example, for operation of
tailgates of trucks or hydrostatic fan drives.

Index

377

Index
A

Accessories
267
Accumulator. 
See "Hydraulic accumulators"
Accumulator charging valves
171
Accumulator circuits
353
for compensation of volume expansion
357
for shock and vibration damping356
for the provision of flow
353
Accumulator shut-off blocks
276
Annular gear motor - gerotor principle
244
Annular gear motors - orbit principle
246
Annular gear pumps
104Applications in industrial hydraulics
10
Applications in mobile hydraulics
12
Axial piston motors - bent axis design
232
Axial piston motors - swash plate design
228
Axial piston pumps – bent axis design
94
Axial piston pumps – swash plate design
89

B

Basic circuits of hydraulics
Basic principles
Basic principles of hydraulics
Basic principles of mechanics
Basic principles of mechanics
Basic principles of physics
Basic principles of hydraulics
Bent axis design
for axial piston motors
for axial piston pumps
Bernoulli, Principle ofBernoulli's Principle
Bladder-type accumulator
Block installation
Bourdon tube pressure switches
Bulk modulus

C

Cavitation
Acoustic cavitation
Cloud cavitation
Layer cavitation
Single-bubble cavitation
Vortex cavitation
Characteristic curves of pumps and motors
for efficiency
for mechanical drive power
for the flow
Characteristic zones
Circuit diagramCircuit diagrams in hydraulicsCircuit schematics

297
25
46
46
25
25
232
94
30
30
272
129
292
40
42
43
43
43
43
43
67
69
68
67
71
298
297
298

Clamping and drive modules
369
Closed-loop control with valves
300
Compact modules
370
Compensation of volume expansion
357
Components
59
Compressibility in the hydraulic system
41
Compressibility of fluids
40
Connection between hydraulic andmechanical quantities
57
Connection elements
for hoses
256
for pipes
256
Connection technologies
251
Overview
251
Requirements
251
Construction types of hydraulic cylinders
198
Control blocks
264
Control of actuators
in parallel operation
348
with lower operating pressure
346
Control systems
with directional control valves
300
with pressure switch
342
Cooler
281, 363
Oil cooler, air-cooled283
Oil cooler, water-cooled
284
Cylinder. 
See "Hydraulic cylinders"
CytroBox
366
CytroPac
366

D

Damping bearingDamping by accumulator circuitsof mechanical shocks
of pulsation and pressure shocks
with stabilization modules
Definition of hydraulics
Diaphragm-type accumulator
Differential cylinder
Differential pressure manometer
Digital manometers
Directional control valves
Control with directional control valves
OverlapSwitching behavior
Switching timeDisplacementDisplacement machines
Displacement principle
Double-acting cylinder
Drive modules
Drive technologies

361
356
356
356
9
272
205
287
294
136
300
146
146
143
61
64
61
213
368
13

378

Index

Comparison
Energy distribution
Energy supply and conversionEnvironmental compatibilityProperties
Transmission medium
Drive units

14
15
15
16
17
16
359, 370

E

Efficiency
Energy and work
External gear motors
External gear pumps

F

Filling level indicator
Filling level measurement
Filter. 
Filter efficiency
Filter intake capacityFilter ratingFine throttle valves (orifices)
Flange fittings
Flow
Laminar flowTurbulent flow
Flow control valves
for synchronous control
Flow dividers
Flow losses in hydraulic lines
Flow measurement
Flow measuring procedures
Force and path transmission
Force and torque
Force transmission
Friction factor

55
52
217
75
362
294
See "Hydrofilter"
280
280
280
183
258
37
37
185
351
352
39
295
295
27
48
27
38

G

Gerotor principle for annular gear motors
244
Graphical symbols. 
See "Graphic symbols"
Graphic symbols
18

H

Heating (of a hydraulic power unit)
High-pressure filter
History of hydraulics
Hose lines
Hydraulic accumulators
Accumulator shut-off blocks
Bladder-type accumulator
Circuits
Diaphragm-type accumulator
Piston-type accumulator
Safety of hydraulic accumulators
Hydraulic circuit systems
Hydraulic cylinder end position damping

363
278
9
254
267
276
272
353
272
273
275
316
196

Hydraulic cylinders
Basic principlesComparison of construction types
Double-acting hydraulic cylindersEnd position dampingMill type design
Mounting types
Single-acting hydraulic cylinders
Tie rod design
Hydraulic filters
High-pressure filter
Return filter
Suction filter
Hydraulic fluids
Hydraulic fluid temperature measurementHydraulic motors
Axial piston motors - bent axis design
Axial piston motors - swash plate design
External gear motors
Internal gear motors
Radial piston motors with external support
Radial piston motors with internal support
Vane motors
Hydraulic motors in comparisonHydraulic power units
Hydraulic power units in comparisonHydraulic pumps
Annular gear pumps
Axial piston pumps – bent axis design
Axial piston pumps – swash plate design
External gear pumps
Internal gear pumps
Pump regulating systems
Radial piston pumps with internal support
Radial piston pump with external support
Screw pumps
Vane pumps
Hydraulic pumps in comparisonHydraulic systems
Hydraulic training systems
Hydraulic valve designs
Block installation
In-line installation
Monoblock
Sandwich plate design
Stack valves
Subplate mountingHydraulic valves
Cavitation occurrence in hydraulic valves
CharacteristicsDesigns
Operating elements
Overview
Type designation
Types of operation
Valve operation
Hydrodynamics - Bernoulli's Principle
Hydrostatic drives

191
191
198
194
196
195
197
194
195
277
278
278
278
59
296
217
232
228
217
221
241
237
224
250
359
371
75
104
94
89
75
81
109
99
102
106
83
121
359
374
127
129
128
130
130
129
128
125
45
131
127
130
125
132
130
130
30
316

IndexHydrostatic operating principles
Hydrostatics – Pascal's LawI

Individual power units
In-line installation
Internal gear motors
Internal gear pumps
ISO 1219 - Extract

J

Jerk
Jerk limitation

L

Laminar flow
Large power units
Low-noise compact power units –Silent power units

316
25
368
128
221
81
22
47
48
37
366
367

M

Manifolds
262
Manometer
286
Differential pressure manometer
287
Digital manometers
294
Load capacity of manometers
290
Manometer selector switch
288
Relative pressure manometer
286
Manometer selector switch
288
Measuring coupling. 
See "Measuring ports"
Measuring ports
258
Metering orifice. 
See "Flow control
valve - Functionality"
Mill type design (of hydraulic cylinders)
195
Minimess ports. 
See "Measuring ports"
Modular large power units
366
Modular standard power units
364
Modular standard small power units
365
Monoblock
130
Motor-pump group361
Motors. 
See "Hydraulic motors"
Mounting types for hydraulic cylinders
197

N

Non-return valvesNon-return valves, pilot-operated

O

172
175

Oil cooler, air-cooled283
Oil cooler, water-cooled284Open-loop control with valves
300
Operating behavior of directional
control valves
143
Operating elements of hydraulic valves
130
Orbit principle for annular gear motors
246
Orifices. 
See "Fine throttle valves"

Orifices in hydraulic lines
Overlap for directional control valves

P

379

35
146

Parallel connection of actuators
348
Parallel operation without synchronization
350
Pascal, Law of
25
Pascal's Law25
Path transmission
28
Pipe and hose lines
254
Pipe flows
37
Pipelines
254
Piston-type accumulator
273
Piston type pressure switches
292
Poppet valves
128
Positioning process
47
Power (physical)
54
Power units
359"Predefined flow" operating principle
322"Predefined power" operating principle
338"Predefined pressure difference"
operating principle
334"Predefined pressure" operating principle
329"Predefined speed" operating principle
335
Prefill valves
178
Preload valves
165
Pressure and force-depending
control systems
339
Pressure compensator. See "Flow control valve - Functionality"
Pressure cut-off valves
168
Pressure dependence of the hydraulic fluid
40
Pressure drop in pipe flows
38
Pressure indicators, analog. 
See "Manometer"
Pressure indicators, digital
294
Pressure intensification
29
Pressure intensifiers
342
Pressure limitation
339
Pressure medium
59
Pressure reducing valves
156
Pressure reduction
between directional control
valve and actuator
346
in the supply of directional control valves
347
Pressure relief valves
148
Pressure sensors. 
See "Pressure sensors"
Pressure sequence valves
162
Pressure switches
290, 342
Bourdon tube pressure switches292
for monitoring the filter function
345
in accumulator charging control
345
in sequence control for pressure increase 342
Piston type pressure switches
292

380

Index

Pressure switch; electronic
292
Pressure transducer
293
Principle of conservation of momentum
53
Pulsation absorber
361
Pump regulating systems
109
Pumps. 
See "Hydraulic pumps"

Q

Quick couplings

R

Radial piston motors with external support
Radial piston motors with internal support
Radial piston pumps with internal support
Radial piston pump with external support
Ram type cylinderRapid traverse circuits
Relative pressure manometer
Return filter
Reynolds Number

S

256
241
237
99
102
199
312
286
278
37

Sandwich plate design
130
Screw-in cartridge valves
129
Screw pumps
106
Sensors for hydraulic fluid temperature
measurement
296
Sensors for pressure measurement.

See "Pressure sensors"
Sequence valves
164
Servo cylinders
209
Shuttle valves
174
Silent power units
367
Slip-in cartridge valves
129
Spool valves
127
Stabilization modules
356
Stack valves
129Standard power units
364Standard small power units
365
Subplate mounting
128
Suction filter
278
Supply systems (CytroPac, CytroBox)
366
Swash plate design
for axial piston motors
228
for axial piston pumps
89
Symbols. 
See "Graphic symbols"
Synchronization control
with flow control valves
351
with flow divider
352
Sytronix pump drives
372

T

Tank. See "Tank"
telescopic cylinder
201
Temperature dependence of the hydraulic fluid 40
Temperature measurement of hydraulic fluids 296
Threaded fittings
257
Throttle/non-return valves
183
Throttle valves
180
for velocity control
304
Tie rod design (of hydraulic cylinders)
195
Torque50
Torque balance
50
Training power units.
See "Training systems in hydraulics"
Training systems in hydraulics(training power units)
374
Turbulent flow
37Type designation of hydraulic valves
132
Types of operation of hydraulic valves
130
direct-operated valve
130
electrical operation
134
Hydraulic or pneumatic operation
134
pilot-operated valve
130

U

Ultrasonic measuring procedure for flow
measurement
Units of measurement of pressure
Unloading valves

296
25
165

V

Valve operation
130
direct-operated valve
130
pilot-operated valve
130
Valves. 
See "Hydraulic valves"
Vane motors
224
Vane pumps
83
Variable speed pump drives (Sytronix)
372
Velocity control with flow control valves
309
Velocity control with throttle valves
304
Vertical stacking260
Viscosity
Dynamic viscosity
31
Kinematic viscosity
31
Viscosity classes
33
Viscosity index
33
Viscosity of fluids
31

W

Work (physical)
Workstation. 

53
See "Training systems"

Bosch Rexroth AG
Bosch Rexroth Academy
Unterduerrbacher Straße 1097080 Wuerzburg, Germany
Phone: +49 9352 18-1920
E-Mail:		 training@boschrexroth.dewww.boschrexroth.com/academy

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R901566373 (2022.11 · EN · Printed in Germany)© Bosch Rexroth AG 2022