Mobile Hydraulics - Festo Didactic

WorkbookTP 800

With CD-ROM

Festo Didactic

574166 en

Mobile Hydraulics

TP

D (X2) A B

LS

C (X1)

P

C

T

B

LSLS2

T

A

D

LS1

P

Order no. 574166

Revision level: 03/2013

Authors: Ulrich Schedel, Levent Unan

Editor: Christine Löffler

Graphics: Doris Schwarzenberger

Layout: 03/2013, Susanne Durz, Christine Löffler

© Festo Didactic GmbH & Co. KG, 73770 Denkendorf, 2013

Internet: www.festo-didactic.com

e-mail: [email protected]

The purchaser shall receive a single right of use which is non-exclusive, non-time-limited and limited

geographically to use at the purchaser's site/location as follows.

The purchaser shall be entitled to use the work to train his/her staff at the purchaser's site/location and

shall also be entitled to use parts of the copyright material as the basis for the production of his/her own

training documentation for the training of his/her staff at the purchaser's site/location with

acknowledgement of source and to make copies for this purpose. In the case of schools/technical colleges

and training centres, the right of use shall also include use by school and college students and trainees at

the purchaser's site/location for teaching purposes.

The right of use shall in all cases exclude the right to publish the copyright material or to make this available

for use on intranet, Internet and LMS platforms and databases such as Moodle, which allow access by a

wide variety of users, including those outside of the purchaser's site/location.

Entitlement to other rights relating to reproductions, copies, adaptations, translations, microfilming and

transfer to and storage and processing in electronic systems, no matter whether in whole or in part, shall

require the prior consent of Festo Didactic GmbH & Co. KG.

© Festo Didactic GmbH & Co. KG 574166 III

Contents

Intended use ___________________________________________________________________________ VIII

Preface ______________________________________________________________________________ IX

Introduction _____________________________________________________________________________ XI

Work and safety instructions ______________________________________________________________ XII

Mobile hydraulics training package (TP 800) _________________________________________________ XIV

Learning objectives ______________________________________________________________________ XV

Allocation of learning objectives to exercises _________________________________________________ XVII

Equipment set __________________________________________________________________________ XX

Allocation of components to exercises ____________________________________________________ XXVII

Notes for the teacher/trainer ______________________________________________________________ XXX

Structure of the exercises ________________________________________________________________ XXXI

Component designations _________________________________________________________________ XXXI

CD-ROM contents _______________________________________________________________________ XXXI

Exercises and solutions: Mobile hydraulics, basic level working hydraulics (TP 801)

Exercise 1-1: Examining performance for a controller using constant displacement pump

and fixed pressure limitation ____________________________________________________ 3


and adjusted pressure limitation using open-centre load-sensing pressure balance _____ 13

Exercise 1-3: Examining performance of speed control using a 6/3-way proportional valve ___________ 23

Exercise 1-4: Examining energy efficiency of speed control in an open-centre load-sensing system ____ 31

Exercise 1-5: Moving and holding a load with a 6/3-way proportional valve _______________________ 41

Exercise 1-6: Moving and holding a load with a piloted non-return valve __________________________ 51

Exercise 1-7: Moving and holding a load with a pressure-relief valve as counter pressure ____________ 59

Exercise 1-8: Moving and holding a load with a counterbalancing valve ___________________________ 69

Exercise 1-9: Examining parallel, series and tandem configurations ______________________________ 79

Exercises and solutions: Mobile hydraulics, advanced level steering system (TP 802)

Exercise 2-1: Examining the steering valve in a hydrostatic steering system _______________________ 91

Exercise 2-2: Examining steering when external forces are exerted ______________________________ 99

Exercise 2-3: Examining overload protection for steering _____________________________________ 107

Exercise 2-4: Examining a steering system with priority function _______________________________ 115

Exercise 2-5: Designing a steering system for centre-pivot steering _____________________________ 123

IV © Festo Didactic GmbH & Co. KG 574166

Exercises and solutions: Mobile hydraulics, advanced level working hydraulics (TP 803)

Exercise 3-1: Examining a hydraulic system with load-sensing-controlled variable displacement pump 133

Exercise 3-2: Examining the load hold function _____________________________________________ 143

Exercise 3-3: Remotely controlling proportional directionalcontrol valves using a hydraulic joystick __ 151

Exercise 3-4: Setting a (volumetric) flow rate independent of load ______________________________ 159

Exercise 3-5: Setting the volumetric flow rate using a load-sensing-controlled pump unit ___________ 169

Exercise 3-6: Examining a load-sensing system with upstream pressure balance __________________ 179

Exercise 3-7: Examining a load-sensing system with downstream pressure balance ________________ 191

Exercises and worksheets: Mobile hydraulics, basic level working hydraulics (TP 801)












Exercises and worksheets: Mobile hydraulics, advanced level steering system (TP 802)






Exercises and worksheets: Mobile hydraulics, advanced level working hydraulics (TP 803)



Exercise 3-3: Remotely controlling proportional directional control valves using a hydraulic joystick __ 151





© Festo Didactic GmbH & Co. KG 574166 V

Basics of mobile hydraulics

1 Introduction _____________________________________________________________________ I-5

2 Fundamentals of hydraulics ________________________________________________________ I-7

2.1 Basic principles of pressure and flow control valves _____________________________________ I-7

2.2 Pressure drop ___________________________________________________________________ I-10

2.3 Heat generation due to the pressure drop ____________________________________________ I-13

3 Closed hydraulic circuit (hydrostatic system) _________________________________________ I-15

3.1 Setting up a closed hydraulic circuit _________________________________________________ I-15

3.2 Hydraulic pumps for closed hydraulic circuits _________________________________________ I-17

3.2.1 Mechanically resetting the hydraulic pump ___________________________________________ I-17

3.2.2 Hydraulically resetting the hydraulic pump ___________________________________________ I-18

3.3 Feed pumps _____________________________________________________________________ I-20

3.4 Flushing valves __________________________________________________________________ I-20

3.5 Shock valves ____________________________________________________________________ I-21

4 Load-sensing systems ____________________________________________________________ I-23

4.1 Attributes of load-sensing systems __________________________________________________ I-23

4.1.1 Open-centre load-sensing systems __________________________________________________ I-23

4.1.2 Closed centre load-sensing systems _________________________________________________ I-25

4.2 Energy efficiency of the hydraulic pressure supply _____________________________________ I-30

4.2.1 Loss of energy ___________________________________________________________________ I-30

4.2.2 Pressureless pump recirculation circuit ______________________________________________ I-32

4.2.3 Flow rate control in systems with constant displacement pump ___________________________ I-34

4.2.4 Flow rate control in systems with variable displacement pump ___________________________ I-36

4.2.5 Flow rate control in open-centre load-sensing systems __________________________________ I-38

4.2.6 Flow rate control in closed centre load-sensing systems _________________________________ I-40

5 Variable-displacement pumps _____________________________________________________ I-42

5.1 Types of variable displacement pumps _______________________________________________ I-42

5.2 Vane pump _____________________________________________________________________ I-42

5.3 Axial piston pump ________________________________________________________________ I-44

6 Two-pump system with shut-off valve _______________________________________________ I-46

6.1 Requirements of a pump system for mobile machines ___________________________________ I-46

6.2 Example of a two-pump system with shut-off valve _____________________________________ I-47

7 Flow dividers ___________________________________________________________________ I-48

7.1 Synchronicity of drives ____________________________________________________________ I-48

7.2 Flow divider (50/50 slide valve) _____________________________________________________ I-48

7.3 Rotation flow valve _______________________________________________________________ I-50

7.4 Rotation flow valve for pressure boosting _____________________________________________ I-51

VI © Festo Didactic GmbH & Co. KG 574166

8 Valve manifold for mobile hydraulics _______________________________________________ I-49

8.1 Setup of valve blocks _____________________________________________________________ I-53

8.2 Circuit symbol of proportional directional control valves in valve modules __________________ I-55

8.3 Setup of valve modules ___________________________________________________________ I-56

8.4 Valve slides of proportional directional constant valves _________________________________ I-57

8.4.1 Design of valve slides _____________________________________________________________ I-57

8.4.2 Influence of control notches on flow rate characteristics _________________________________ I-58

8.5 Input module of a valve manifold ___________________________________________________ I-59

8.5.1 Design of an input module _________________________________________________________ I-59

8.5.2 Input module in combination with an open-centre valve module __________________________ I-60

8.5.3 Input module in combination with a closed-centre valve module __________________________ I-61

8.6 Shock and anti-cavitation valve _____________________________________________________ I-62

9 Circuits with open-centre valves ____________________________________________________ I-64

9.1 Open-centre valves _______________________________________________________________ I-64

9.2 Design of an open-centre 6/3-way valve ______________________________________________ I-66

9.3 Parallel connection _______________________________________________________________ I-69

9.4 Tandem configuration ____________________________________________________________ I-70

9.5 Series connection ________________________________________________________________ I-71

10 Load-independent flow rate control with proportional valves ____________________________ I-72

10.1 Proportional flow control valve _____________________________________________________ I-72

10.2 Upstream pressure balance ________________________________________________________ I-74

10.3 Downstream pressure balance _____________________________________________________ I-78

11 Holding and safe lowering of load __________________________________________________ I-82

11.1 Application example ______________________________________________________________ I-82

11.2 Piloted non return valve ___________________________________________________________ I-83

11.3 Pressure-relief valve ______________________________________________________________ I-84

11.4 Counterbalancing valve ___________________________________________________________ I-85

12 Hydraulic pilot control ____________________________________________________________ I-88

12.1 Hydraulic pilot control with a joystick ________________________________________________ I-88

13.2 Hydraulic joystick (manually-operated pilot control) ____________________________________ I-88

13.3 Electronic joystick (electro-hydraulic pilot control) _____________________________________ I-90

13 Prioritising consuming devices _____________________________________________________ I-92

13.1 Necessity of prioritising consuming devices ___________________________________________ I-92

13.2 Pressure sequence valve __________________________________________________________ I-92

13.3 Circuit prioritisation ______________________________________________________________ I-93

13.4 Way valves with prioritisation ______________________________________________________ I-94

13.5 Static prioritity valve______________________________________________________________ I-94

13.6 Dynamic priority valve ____________________________________________________________ I-95

13.7 3-way flow control valve ___________________________________________________________ I-96

© Festo Didactic GmbH & Co. KG 574166 VII

14 Hydrostatic steering _____________________________________________________________ I-98

14.1 Design and characteristics of hydrostatic steering ______________________________________ I-98

14.2 Design of steering valves __________________________________________________________ I-98

14.2.1 Rotary slide valve and bush ________________________________________________________ I-99

14.2.2 Proportioning pump (Orbitrol pump) ________________________________________________ I-100

14.3 Versions of steering valves _______________________________________________________ I-101

14.3.1 Open-centre steering valves ______________________________________________________ I-101

14.3.2 Closed-centre steering valves _____________________________________________________ I-102

14.3.3 Load-sensing steering valves ______________________________________________________ I-103

14.3.4 Reaction and non-reaction steering valves ___________________________________________ I-103

14.4 Types of steering systems ________________________________________________________ I-104

14.4.1 Ackermann steering system with axle journal steering _________________________________ I-105

14.4.2 Articulated steering system _______________________________________________________ I-105

Picture credits ________________________________________________________________________ I-107

© Festo Didactic GmbH & Co. KG 574166 VIII

Intended use

The mobile hydraulics basic and advanced level training packages are only to be used:

for the intended purpose in teaching and training applications

when their safety functions are in flawless condition

The components in the training packages are designed in accordance with the latest technology as well as

recognised safety rules. However, life and limb of the user and third parties may be endangered, and the

components may be impaired, if they are used incorrectly.

The learning system from Festo Didactic has been developed and produced exclusively for training and

continuing vocational education in the field of automation technology. The training companies and/or

trainers must ensure that all trainees observe the safety instructions described in this workbook.

Festo Didactic hereby excludes all liability for damage suffered by the trainee, the training company and/or

any other third parties as a result of use of these equipment sets outside a purely training situation, unless

Festo Didactic has caused this damage wilfully or through gross negligence.

© Festo Didactic GmbH & Co. KG 574166 IX

Preface

Festo Didactic’s training system for automation and technology is geared towards various educational

backgrounds and vocational requirements. The learning system is therefore broken down as follows:

Technology oriented training packages

Mechatronics and factory automation

Process automation and control technology

Mobile robotics

Hybrid learning factories

The training system for automation and technology is continuously updated and expanded in accordance

with developments in the field of education, as well as actual professional practice.

The training packages deal with various technologies including pneumatics, electro-pneumatics,

servopneumatics, hydraulics, electro-hydraulics, proportional hydraulics, servohydraulics, mobile

hydraulics, programmable logic controllers, sensor technology, electrical engineering, electronics and

electric drives.

The modular design of the training system allows for applications which go above and beyond the

limitations of the individual training packages. For example, PLC actuation of pneumatic, hydraulic and

electric drives is possible.

X © Festo Didactic GmbH & Co. KG 574166

All training packages feature the following elements:

Hardware

Media

Seminars

Hardware

The hardware in the training packages is comprised of industrial components and systems that are specially

designed for training purposes. The components contained in the training packages are specifically

designed and selected for the projects in the accompanying media.

Media

The media provided for the individual topics consist of a mixture of teachware and software. The teachware

includes:

Technical literature and textbooks (standard works for teaching basic knowledge)

Workbooks (practical exercises with supplementary instructions and sample solutions)

Lexicons, manuals and technical books

(which provide technical information on groups of topics for further exploration)

Transparencies and videos (for easy-to-follow, dynamic instruction)

Posters (for presenting information in a clear-cut way)

Within the software, the following programmes are available:

Digital training programmes (learning content specifically designed for virtual training)

Simulation software

Visualisation software

Software for acquiring measurement data

Project engineering and design engineering software

Programming software for programmable logic controllers

The teaching and learning media are available in several languages. They are intended for use in classroom

instruction, but are also suitable for self-study.

Seminars

A wide range of seminars covering the contents of the training packages round off the system for training

and vocational education.

Do you have suggestions or criticism regarding this manual?

If so, send us an e-mail at [email protected].

The authors and Festo Didactic look forward to your comments.

© Festo Didactic GmbH & Co. KG 574166 XI

Introduction

This workbook is part of the training system for automation technology from Festo Didactic GmbH & Co. KG.

The system provides a solid basis for practice oriented training and vocational education. The mobile

hydraulics workbook communicates the basics and fundamental knowledge on the hydraulic systems of

mobile work machines.

The contents of the workbook are project exercises on the basic level of working hydraulics (TP 801),

advanced level steering systems (TP 802) and advanced level working hydraulics (TP 803). The workbook

also contains a basic information section on mobile hydraulics.

The basic level working hydraulics (TP 801) is suitable for basic training in mobile hydraulics.

Using practice-related problem descriptions, the energy balances of different hydraulic systems (also while

loaded) will be examined and evaluated. Control systems with multiple consuming devices are set up in

parallel, tandem and series connections and examined in relation to priority, flow rate distribution, and

pressure dependency. Further course topics are the behaviour of consuming devices while under loads and

the options for safely holding and lowering a load. Basic knowledge of hydraulic device technology is a

prerequisite.

The advanced level steering system (TP 802) communicates the basics of hydrostatic steering systems with

suitable hydraulic controls. The controllers contain typical components of a steering system like steering

valve, shock and anti-cavitation valve, steering cylinder and, if required, a secondary consuming device.

In the project exercises for advanced level working hydraulics (TP 803), details of the working hydraulics are

expanded upon and hydraulic controls with load-sensing controlled variable displacement pump will be set

up and examined.

Technical prerequisites for setting up the controllers include:

A Learnline or Learntop-S workstation equipped with Festo Didactic slotted profile plates.

A hydraulic power unit with constant displacement pump (volumetric flow rate: 4 l/min) for TP 801 and

TP 802, a hydraulic power unit with constant displacement pump (volumetric flow rate: 4 l/min) and

load-sensing controlled variable displacement pump for TP 803.

A power pack with short-circuit protection (input: 230 V, 50 Hz, output: 24 V, max. 5 A).

Laboratory safety cables

The practical execution of the nine project exercises for TP 801 requires a TP 801 equipment set. One TP 801

and TP 802 equipment set is required for the practical execution of each of the five project exercises for

TP 802. An additional TP 803 equipment set is necessary for the practical execution of the seven project

exercises for TP 803.

The theoretical fundamentals for understanding these exercises can be found in the following textbooks:

Hydraulics, basic level

Electro-hydraulics, basic level

as well as in the appendix to this workbook.

Data sheets for the individual components are also available (cylinders, valves, sensors etc.).

XII © Festo Didactic GmbH & Co. KG 574166

Work and safety instructions

General

Trainees should only work with the circuits under the supervision of a trainer.

Electrical devices (e.g. power supply units, compressors and hydraulic power units) may only be

operated in laboratory rooms which are equipped with residual current devices (RCDs).

Observe specifications included in the technical data for the individual components, and in particular all

safety instructions!

Malfunctions which may impair safety must not be generated in the training environment, and must be

eliminated immediately.

Wear personal safety gear (safety glasses, safety shoes) when working on circuits.

Mechanical system

Only reach into the setup when it is at a complete standstill.

Mount all of the components securely onto the slotted profile plate.

Limit switches may not be actuated frontally.

Danger of injury during troubleshooting!

Use a tool to actuate the limit switches, for example a screwdriver.

Set all components up so that activation of switches and disconnectors is not made difficult.

Adhere to the instructions regarding positioning of the components.

Always set up cylinders together with the appropriate cover.

Electrical functions

Use extra-low voltage only (max. 24 V DC).

Establish or interrupt electrical connections only in the absence of voltage!

Use only connecting cables with safety plugs for electrical connections.

When disconnecting connector cables, only pull by the plug, never by the cable.

Hydraulics

Limit system pressure to 6 MPa (60 bar).

Maximum permissible pressure for all devices included in the training package is 12 MPa (120 bar).

In the case of double-acting cylinders, pressure could be increased relative to the surface area ratio due

to pressure boosting. With a surface area ratio of 1:1.7 and a system pressure of 6 MPa (60 bar), it may

amount to more than 10 MPa (100 bar).

Danger of injury due to oil temperatures of greater than 50° C!

Hydraulic fluid with an oil temperature of greater than 50° C may result in burns or scalding.

© Festo Didactic GmbH & Co. KG 574166 XIII

Danger of injury when switching on the hydraulic power unit!

Cylinders may extend and retract automatically.

Connecting tubing lines

– Never connect or disconnect tubing lines when the hydraulic power unit is running, or while under

pressure!

Couplings must be connected in the unpressurised state.

– Set the coupling socket vertically onto the coupling nipple!

The coupling socket and the coupling nipple must not be fitted askew.

– After each disconnection, make sure that the couplings have closed themselves!

Hydraulic circuit assembly

– The hydraulic power unit and the electrical power pack

must be switched off when assembling the circuit.

– Before commissioning, make sure that all tank lines have been connected

and that all couplings have been securely fitted.

– Make sure that tubing lines connected to the cylinder are rinsed with hydraulic fluid,

if the volume of oil accommodated by the cylinder is less than the volume which can

be contained by the tubing lines.

Commissioning

– Cylinders may only be commissioned with their covers in place.

– Switch on the electrical power pack first, and then the hydraulic power unit.

Dismantling hydraulic circuits

– Assure that pressure has been relived before dismantling the circuit.

– Switch off the hydraulic power unit first, and then the electrical power pack.

If connections are decoupled while under pressure, pressure is trapped in the device by the non-return

valve in the coupling. This pressure can be vented with the pressure relief unit.

Mounting technology

The mounting boards for the components are equipped with mounting variant A, B or C:

Variant A, snap-in system

Lightweight devices which cannot be subjected to loads (e.g. directional control valves and sensors).

Simply clip the components into the slots on the slotted profile plate. Release the components from the

slots by actuating the blue lever.

Variant B, rotary system

Components with medium load capacity (e.g. hydraulic cylinders). These components are clamped to

the slotted profile plate with T-head bolts. The blue knurled nut is used for clamping and loosening.

Make sure that the T-head bolts have been turned 90° after tightening.

Variant C, screw system

For devices with high load capacity and devices which are seldom removed from the slotted profile plate

(e.g. the hydraulic power unit). These devices are fastened with socket head screws and T-head nuts.

Required accessories

Two digital multimeters are required to evaluate exercises which make use of the flow sensor.

The output voltage of the flow sensor is measured with the multimeter.

XIV © Festo Didactic GmbH & Co. KG 574166

Mobile hydraulics training package (TP 800)

The TP 800 training package consists of a multitude of individual training materials. This package refers to

components and basic circuits of the hydraulic systems of working machines. Individual components from

training package TP 800 may also be included in other packages.

Important TP 800 components

Permanent workstation with Festo Didactic profile plate

Equipment sets or individual components (e.g. cylinders, valves and pressure gauges)

Complete set of laboratory equipment

Media

The teachware for the training package TP 800 consists of one workbook. The contents of the workbook are

the project exercises on the basic level of working hydraulics (TP 801), advanced level steering systems

(TP 802) and advanced level working hydraulics (TP 803). The theoretical fundamentals for understanding

the exercises are described in the textbook attachment.

The workbook includes the exercise sheets and worksheets for the project exercise, the solutions to each

individual worksheet and a CD-ROM. A set of ready-to-use exercise sheets and worksheets is included in

each workbook for all of the exercises.

Data sheets for the hardware components are made available along with the equipment set.

Media

Textbooks Hydraulics, basic level

Electro-hydraulics, basic level

Workbooks Mobile hydraulics (TP 800)

Set of posters Hydraulics

Simulation programme FluidSIM® Hydraulic

TP 810 Diagnostic system FluidLab® M

Digital training programme Web-based training, hydraulics – Basics of hydraulics principles

Web-based training electro-hydraulices – Basics of electro-hydraulics principles

Overview of media for training package TP 800

The media are offered in several languages. Further training materials can be found in our catalogues and on

the Internet.

© Festo Didactic GmbH & Co. KG 574166 XV

Learning objectives

Mobile hydraulics: Basic level working hydraulics (TP 801)

To know the relationship between pressure, flow rate and power output.

To be able to calculate the power consumption of a hydraulic system.

To know that flow division can lead to energy losses in a hydraulic system.

To know that when using a constant displacement pump, non-decreasing volume flow leads to energy

loss.

To know how a constant displacement pump with an open-centre load-sensing pressure balance works.

To know the power-relevant advantages of a constant displacement pump with pressure regulation by

an open-centre load-sensing pressure balance over a constant displacement pump without an open-

centre load-sensing pressure balance.

To be familiar with the mode of operation of a 6/3-way proportional valve.

To know that proportional directional control valves restrict inflow and outflow.

To know that a 6/3-way proportional valve with mid-position tank recirculation only generates minor

energy loss in mid-position.

To know how a shuttle valve works and how to use it.

To understand the control circuit of an open-centre load-sensing system.

To know that a proportional directional control valve in connection with an open-centre load-sensing

pressure balance represents a flow control valve.

To be able to use the cylinder load simulator (loading unit).

To understand the behaviour of the cylinders under load.

To know how to use a delockable double non-return valve for the purpose of secure holding.

To know the advantages and disadvantages of a delockable double non-return valve.

To be able to use a pressure-relief valve as a counter-pressure valve for secure holding and lowering.

To know the advantages and disadvantages of counter-pressure valves.

To be able to use a counterbalancing valve for the secure holding and lowering of a load.

To know the main difference between a counterbalancing valve and a pressure-relief valve.

To know that using a counterbalancing valve can reduce energy when lowering a load.

To know how series, parallel and tandem configurations of 6/3-way proportional valves work.

To be able to describe the advantages and disadvantages of these configuration types for an

application.

XVI © Festo Didactic GmbH & Co. KG 574166

Mobile hydraulics: Advanced level steering system (TP 802)

To understand how the steering valve works.

To know the properties of a non-reaction steering valve.

To understand the behaviour of the steering system under the influence of external forces.

To explain how a shock valve works.

To know for which applications shock valves are to be used.

To understand why it is necessary that one drive in a hydraulic system with multiple drives must

preferably be supplied by oil (priority function).

To know the effects of the priority function.

To know the setup of a centre-pivot steering.

Mobile hydraulics: Advanced level working hydraulics (TP 803)

To be able to explain the load-sensing function of valve manifolds.

To understand how the load-dependent pump pressure regulation (load-sensing) works.

To know the power-relevant advantages of hydraulic systems with load-sensing-controlled variable

displacement pumps.

To know how valve manifolds in mobile hydraulics work and how to use them.

To know the properties of a hydraulic joystick.

To be able to control proportional directional control valves with a hydraulic joystick.

To know the relationship between load changes and speed changes when using a flow control valve.

To know the properties of a 2-way flow control valve.

To know how to maintain a constant speed despite changing loads.

To be able to regulate flow rate with a load-sensing controlled pump unit.

To know the limits of a load-sensing system.

To understand the advantages and disadvantages of the upstream pressure balance in load-sensing

systems.

To be familiar with the mode of operation of the downstream pressure balance.

To know the advantages and disadvantages of the downstream pressure balance in load-sensing

systems.

© Festo Didactic GmbH & Co. KG 574166 XVII

Allocation of learning objectives to exercises

Mobile hydraulics: Basic level working hydraulics (TP 801)

Exercise 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9

Learning objective

To know the relationship between pressure, flow rate and power

output. •

To be able to calculate the power consumption of a hydraulic

system. •

To know that flow division can lead to energy losses in a hydraulic

system. •

To know that when using a constant displacement pump, non-

decreasing volume flow leads to energy loss. •

To know how a constant displacement pump with an open-centre

load-sensing pressure balance works. •

To know the power-relevant advantages of a constant

displacement pump with pressure regulation by an open-centre

load-sensing pressure balance over a constant displacement

pump without an open-centre load-sensing pressure balance.

•

To be familiar with the mode of operation of a 6/3-way

proportional valve. •

To know that proportional directional control valves restrict inflow

and outflow. •

To know that a 6/3-way proportional valve with mid-position tank

recirculation only generates minor energy loss in mid-position. •

To know how a shuttle valve works and how to use it. •

To understand the control circuit of an open-centre load-sensing

system. •

To know that a proportional directional control valve in

connection with an open-centre load-sensing pressure balance

represents a flow control valve.

•

To be able to use the cylinder load simulator (loading unit). •

To understand the behaviour of the cylinders under load. •

To know how to use a delockable double non-return valve for the

purpose of secure holding. •

To know the advantages and disadvantages of a delockable

double non-return valve. •

XVIII © Festo Didactic GmbH & Co. KG 574166

Exercise 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9

Learning objective

To be able to use a pressure-relief valve as a counter-pressure

valve for secure holding and lowering. •

To know the advantages and disadvantages of counter-pressure

valves. •

To be able to use a counterbalancing valve for the secure holding

and lowering of a load. •

To know the main difference between a counterbalancing valve

and a pressure-relief valve. •

To know that using a counterbalancing valve can reduce energy

when lowering a load. •

To know how series, parallel and tandem configurations of 6/3-

way proportional valves work. •

To be able to describe the advantages and disadvantages of these

configuration types for an application. •

Mobile hydraulics: Advanced level steering system (TP 802)

Exercise 2-1 2-2 2-3 2-4 2-5

Learning objective

To understand how the steering valve works. •

To know the properties of a non-reaction steering valve. •

To understand the behaviour of the steering system under the influence of external

forces. •

To explain how a shock valve works. •

To know for which applications shock valves are to be used. •

To understand why it is necessary that one drive in a hydraulic system with multiple

drives must preferably be supplied by oil (priority function). •

To know the effects of the priority function. •

To know the setup of a centre-pivot steering. •

© Festo Didactic GmbH & Co. KG 574166 XIX

Mobile hydraulics: Advanced level working hydraulics (TP 803)

Exercise 3-1 3-2 3-3 3-4 3-5 3-6 3-7

Learning objective

To be able to explain the load-sensing function of valve manifolds. •

To understand how the load-dependent pump pressure regulation (load-

sensing) works. •

To know the power-relevant advantages of hydraulic systems with load-

sensing-controlled variable displacement pumps. •

To know how valve manifolds in mobile hydraulics work and how to use

them. •

To know the properties of a hydraulic joystick. •

To be able to control proportional directional control valves with a

hydraulic joystick. •

To know the relationship between load changes and speed changes when

using a flow control valve. •

To know the properties of a 2-way flow control valve. •

To know how to maintain a constant speed despite changing loads. •

To be able to regulate flow rate with a load-sensing controlled pump unit. •

To know the limits of a load-sensing system. •

To understand the advantages and disadvantages of the upstream

pressure balance in load-sensing systems. •

To be familiar with the mode of operation of the downstream pressure

balance. •

To know the advantages and disadvantages of the downstream pressure

balance in load-sensing systems. •

XX © Festo Didactic GmbH & Co. KG 574166

Equipment set

The equipment sets TP 801, TP 802 and TP 803 are compiled for the basic and advanced level mobile

hydraulics. Equipment set TP 801 includes all of the components which are necessary for mastering the

learning objectives for TP 801. To master the learning objectives for TP 802, you will require the components

of the three equipment sets TP 801 and TP 802. For the setup of the control units for TP 803, you will require

the components of the three equipment sets TP 801, TP 802 and TP 803. The equipment sets can be

supplemented with other equipment sets as desired.

Equipment set: Mobile hydraulics, basic level working hydraulics (TP 801), order no. 574161

Designation Order number Quantity

6/3-way proportional hand lever valve, mid-position with tank recirculation 572141 2

3-way pressure regulator 544337 1

Shut-off valve 152844 1

Double non-return valve, delockable 572151 1

Flow control valve 152842 1

Pressure-relief valve 544335 2

Pressure balance for open-centre load-sensing 572123 1

Electronic pressure switch 548612 2

Flow sensor 567191 2

Hydraulic motor 152858 2

Diaphragm accumulator with shut-off block 152859 1

Non-return valve, opening pressure: 0.6 MPa 548618 1

Delockable counter balance valve (overcentre valve) 572149 1

T-distributor 152847 3

4-way manifold plate with pressure gauge 159395 2

Shuttle valve 572122 1

Cylinder load simulator (loading unit) 572145 1

© Festo Didactic GmbH & Co. KG 574166 XXI

Graphic symbols, equipment set

Component Graphic symbol

6/3-way proportional hand lever valve,

mid-position with tank recirculation

T2P1P2

BT1A

3-way pressure regulator

T

A

P

Shut-off valve

Double non-return valve,

delockable

B1A1

B2A2

Flow control valve

A B

Pressure-relief valve P

T

Pressure balance for open-centre

load-sensing

XT

P

0.55 MPa

P

TX

0.55 MPa

XXII © Festo Didactic GmbH & Co. KG 574166


Electronic pressure switch ISO 1219-1 EN 60617-7

p

2

RD (1)BK1 (4),

BK2 (5),

WH (2)

BU (3)

p

U

SP1

SP2

Flow sensor ISO 1219-1 EN 60617-7

0V (BU)

q

24V (RD)

0 – 10V(BK)

Hydraulic motor

Diaphragm accumulator with shutoff block

1 0 2

TP

Non-return valve, opening pressure:

0.6 MPa

Delockable counter balance valve

(overcentre valve)

X (1:3)

P

T

T-distributor

© Festo Didactic GmbH & Co. KG 574166 XXIII


4-way manifold plate,

with pressure gauge

Shuttle valve B

A2A1

Cylinder load simulator

(loading unit)

A1.2A1.1 A2.1 A2.2

Equipment set: Mobile hydraulics, advanced level steering system (TP 802), order no. 574162


4/3-way hand lever valve, working lines relieved in mid-position, detenting 544344 1

Steering valve (Orbitrol) 572146 1

Shock and replenishing manifold 572148 1

4-way return header, unpressurised 573026 1

Tubing line for unpressurised return 573024 1

XXIV © Festo Didactic GmbH & Co. KG 574166



4/3-way hand lever valve, working lines

relieved in mid-position, detenting

BA

TP

Steering valve (Orbitrol) L R

P ET

Shock and replenishing manifold

T B1

B2

A1

A2

4-way return header, unpressurised

Tubing line for unpressurised return

© Festo Didactic GmbH & Co. KG 574166 XXV

Equipment set: Mobile hydraulics, advanced level working hydraulics (TP 803), order no. 5741632


Flow control valve 152842 2

Pressure balance, downstream 572741 2

Pressure balance, upstream 573023 1

Load-sensing control block 572144 1

Tubing line for unpressurised return 573024 1

T-distributor 152847 1

Pilot controller (joystick), 2x2-channel 572147 1



Flow control valve

A B

Pressure balance, downstream

XA

P

35 kPa

A

P

X

35 kPa

Pressure balance, upstream

XP

A

0.55 MPa

A

PX

0.55 MPa

Load-sensing control block

TP

D (X1.2) A1 B1

LS

D (X2.2) A2 B2

XXVI © Festo Didactic GmbH & Co. KG 574166


Tubing line for unpressurised return

T-distributor

Pilot controller (joystick),

2x2-channel

X1.1

TP

X1.2 X2.1 X2.2

© Festo Didactic GmbH & Co. KG 574166 XXVII

Allocation of components to exercises

Equipment set: Mobile hydraulics, basic level working hydraulics (TP 801)

Exercise 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9

Component

6/3-way proportional hand lever valve, mid-position with tank

recirculation 1 1 1 1 1 1 2

3-way pressure regulator 1 1 1 1

Shut-off valve 1 1 1 1 1 1 1 1 1

Double non-return valve, delockable 1

Flow control valve 1 1 1

Pressure-relief valve 2 1 2 2 1 2

Pressure gauge 1 1

Pressure balance for open-centre load-sensing 1 1

Electronic pressure switch 2 2 2 2 2 2 2 2 2

Flow sensor 2 2 2 2 1 1 1 2

Hydraulic motor 2 2 2 2 1 1 1 2

Diaphragm accumulator with shutoff block 1 1 1 1

Non-return valve, opening pressure: 0.6 MPa 1 1 1 1

Delockable counter balance valve (overcentre valve) 1

T-distributor 1 2 1 2 2 3 2

4-way manifold plate with pressure gauge 2 2 2 2 2 2 2 2 2

Shuttle valve 1

Cylinder load simulator (loading unit) 1 1 1 1


Exercise 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9

Component

Digital multimeter 2 2 2 2 1 1 1 2

Hydraulic power unit with constant displacement pump

(volumetric flow rate: 4 l/min) 1 1 1 1 1 1 1 1 1

Power pack, 24 V DC 1 1 1 1 1 1 1 1 1

Tubing line 9 10 13 15 12 15 16 16 16

XXVIII © Festo Didactic GmbH & Co. KG 574166

Mobile hydraulics equipment set: Advanced level steering system (TP 802)

Exercise 2-1 2-2 2-3 2-4 2-5

Component

4/3-way hand lever valve, working lines relieved in mid-position, detenting 1 1 1

Steering valve (Orbitrol) 1 1 1 1 1

Shock and replenishing manifold 1

4-way return header, unpressurised 1 1 1 1

Tubing line for unpressurised return 1 1 1 1 1

3-way pressure regulator 1 1 1

Shut-off valve 1 1 1 1 1

Pressure gauge 1 1 1

Electronic pressure switch 2 2 2 2

Flow sensor 1

Hydraulic motor 1

Diaphragm accumulator with shutoff block 1 1 1

Non-return valve, opening pressure: 0.6 MPa 1 1 1

Delockable counter balance valve (overcentre valve) 2

T-distributor 1 2 2

4-way manifold plate with pressure gauge 2 2 2 2 2

Cylinder load simulator (loading unit) 1 1 1 1 1

* Components with grey background come from equipment set TP 801.


Exercise 2-1 2-2 2-3 2-4 2-5

Component

Digital multimeter 1

Hydraulic power unit with constant displacement pump

(volumetric flow rate: 4 l/min) 1 1 1 1 1

Power pack, 24 V DC 1 1 1 1

Tubing line 8 13 16 15 9

© Festo Didactic GmbH & Co. KG 574166 XXIX

Mobile hydraulics equipment set: Advanced level working hydraulics (TP 803)

Exercise 3-1 3-2 3-3 3-4 3-5 3-6 3-7

Component

Flow control valve 1 1 2

Pressure balance, downstream 2

Pressure balance, upstream 1 1

Load-sensing control block 1 1 1 1

Tubing line for unpressurised return 1

T-distributor 1

Pilot controller (joystick), 2x2-channel 1

4-way return header, unpressurised 1

Tubing line for unpressurised return 1 1 1 1

Shut-off valve 1

Flow control valve 1 1 1 1

Pressure-relief valve 1 2 2 2

Pressure gauge 1 1

Electronic pressure switch 2 2 2 2 2 2 2

Flow sensor 1 1 2 2 2

Hydraulic motor 1 1 1 2 2

T-distributor 1 2 3 3

4-way manifold plate with pressure gauge 2 2 2 2 2 2 2

Shuttle valve 1 1

Cylinder load simulator (loading unit) 1 1

*) Components with light grey background are components from the equipment set TP 802

**) Components with dark grey background are components from the equipment set TP 801


Exercise 3-1 3-2 3-3 3-4 3-5 3-6 3-7

Component

Digital multimeter 1 1 2 2 2

Hydraulic power unit with a constant displacement pump (volumetric flow

rate: 4 l/min) and load-sensing-controlled variable displacement pump 1 1 1 1 1 1 1

Power pack, 24 V DC 1 1 1 1 1 1 1

Tubing line 10 10 9 8 9 15 16

XXX © Festo Didactic GmbH & Co. KG 574166

Notes for the teacher/trainer

Learning objectives

The basic learning objective of this workbook is to understand, set up, safely commission and analyse using

measurement technology the basic hydraulic circuits of mobile work machines. This knowledge is gained by

means of theoretical questions and by actually setting up the circuits on the slotted profile plate. Direct

interplay of theory and practice ensures fast progress and long-lasting learning. The more specific learning

objectives are documented in the matrix. Concrete, individual learning objectives are assigned to each

exercise.

Required time

The time required for working through the exercises depends on the learner’s previous knowledge of the

subject matter. Each exercise should take approximately 1 to 1½ hours.

Components of the equipment sets

The project exercises of the workbook and associated equipment sets TP 801, TP 802 and TP 803 are

coordinated with each other. For the nine exercises of basic level working hydraulics (TP 801), you will

require the components of a TP 801 equipment set. For the five exercises of the advanced level steering

system (TP 802), you will require the components of each of the TP 801 and TP 802 equipment sets. For the

seven exercises of advanced level working hydraulics (TP 803), you will require the components of the three

equipment sets TP 801, TP 802 and TP 803.

Standards

The following standards are applied in this workbook:

DIN ISO 1219-1 Fluid power systems and components – Graphic symbols and

circuit diagrams

EN 60617-2 to EN 60617-8 Graphic symbols for diagrams

EN 81346-2 Industrial systems, installations and equipment and industrial products;

structuring principles and reference designations

Identification in the workbook

Solutions and supplements in graphics or diagrams appear in red.

Components used to simulate the load for the application have grey backgrounds in the circuit diagram.

Classifications in the set of exercises

Texts which require completion are identified with a grid or grey table cells.

Graphics and diagrams which require completion include a grid.

Notes for the lesson

Additional information is provided here regarding the didactic-methodological procedure, the individual

components and the completed controllers. These notes are not included in the set of exercises.

© Festo Didactic GmbH & Co. KG 574166 XXXI

Solutions

The solutions specified in this workbook result from test measurements. The results of your measurements

may deviate from these.

Structure of the exercises

All of the project exercises of the basic level TP 801 and the two advanced levels TP 802 and TP 803 have the

same methodical structure. The tasks and are broken down into:

Title

Learning objectives

Problem description

Positional sketch

Project assignments

Work aids

Worksheets

The workbook includes the solutions for all of the worksheets for all exercises.

Component designations

Components are designated in circuit diagrams in accordance with DIN ISO 1219-2. All of the components

included in any given circuit have the same primary identifying number. Letters are assigned depending on

each respective type of component. Consecutive numbers are assigned if several components of the same

type are included within a single circuit.

Cylinders: 1A1, 2A1, 2A2 ...

Valves: 1V1, 1V2, 1V3, 2V1, 2V2, 3V1 …

Sensors: 1B1, 1B2 ...

Signal input: S1, S2 …

Accessories: 0Z1, 0Z2, 1Z1 …

CD-ROM contents

The workbook is included on the CD-ROM as a PDF file. The CD-ROM also provides you with additional

media.

The CD-ROM contains the following folders:

Operating instructions

Illustrations

Data sheets

XXXII © Festo Didactic GmbH & Co. KG 574166

Operating instructions

Operating instructions are provided for various components included in the training package. These

instructions are helpful when using and commissioning the components.

Illustrations

Photos and graphics of components and industrial applications are made available. These can be used to

illustrate individual tasks or to supplement project presentations.

Data sheets

The data sheets for the components included in the training package are supplied along with the equipment

set, and are additionally available as PDF files.

© Festo Didactic GmbH & Co. KG 574166 1

Contents

Exercises and solutions: Mobile hydraulics, basic level working hydraulics (TP 801)




and adjusted pressure limitation using open-centre load-sensing pressure balance ______ 13


Exercise 1-4: Examining energy efficiency of speed control in an open-centre load-sensing system _____ 31

Exercise 1-5: Moving and holding a load with a 6/3-way proportional valve ________________________ 41





2 © Festo Didactic GmbH & Co. KG 574166


Exercise 1-1

Examining performance for a controller using constant displacement pump

and fixed pressure limitation

Learning objectives

After completing this exercise:

you will be familiar with the relationship between pressure, flow rate and power output.

you will be able to calculate the power consumption of a hydraulic system.

you will know that flow division can lead to energy losses in a hydraulic system.

you will know that when using a constant displacement pump, non-decreasing volume flow leads to

energy loss.

Problem description

The motor speed of a wheel milling cutter is controlled using a flow control valve. The rotation of the motor

is only in one direction. The load acting on the motor changes depending on the soil conditions.

Examine how different load requirements affect the energy balance of the controls.

Positional sketch

Wheel saw, © Bobcat, www.bobcat.eu

Exercise 1-1 – Examining performance for a controller using constant displacement pump and fixed pressure limitation


Parameters

When the hydraulic power unit is switched on, the motor will turn.

The load on the motor should be simulated using a proportional pressure-relief valve.

Project assignments

1. Set up the controller.

2. Familiarise yourself with the commissioning procedure.

3. Find out about the procedure when taking measurements in the electrical circuit.

4. Double check the controller configuration.

5. Measure the pressure and flow rate at different load pressures.

6. Calculate the power output of the pump unit; the effective power and the power loss based on the

measured values. Depict the calculated power output in the bar chart and evaluate the results.

Visual inspection

Continuous visual inspection for defects in tubing and hydraulic devices is an essential part of

hydraulic safety standards.

Work aids

Data sheets, operating instructions

Hydraulics textbook

Basics of mobile hydraulics (see attachment)



1. Setting up the controller

1B3

0Z1

1V1

p2

1V3

1B4

45 bar

P2LS T T L L LA LAP1

60 bar

P

Tp1

1V4

1V2

P

Tq2

n

1B21A1

n

1B1

q1

A

B

Circuit diagram

Note for the lesson

The shut-off valve is used for switching pump recirculation. This type of commissioning circuit is

used for all of the exercises below as well.

Electronic pressure switches are used to display precise pressure values.

If the hydraulic motor is only used in connection with a flow sensor, the combination of the two will

be given the equipment designation B for a sensor. If the hydraulic motor is an independent driving

component of the control system, it will be given its own designation A (also only in connection with

a flow sensor).

Note

The pressure-relief valve 1V4 is used to set load pressures.



Quantity Labelling Designation

2 1B3, 1B4 Electronic pressure switch

2 1B1, 1B2 Flow sensor, coupled with hydraulic motor

1 1A1 Hydraulic motor

1 1V3 Flow control valve

2 1V1, 1V4 Pressure-relief valve

1 1V2 Shut-off valve

2 — 4-way manifold plate with pressure gauge

9 — Tubing line

1 0Z1 Hydraulic power unit with constant displacement pump

Equipment list

Note

You will need the following in order to perform the measurements.

• 1 power pack 24 V DC

• 2 digital multimeters

– Set up the controller.

Observe the following points when setting up the controller:

Set the pressure-relief valve for the constant displacement pump of the hydraulic power unit to a

pressure of 60 bar (6 MPa) before setting up the control.

Use the circuit diagram.

Designate the components.



pressure!




Selecting and laying tubing lines

– Select the tubing line length such that adequate leeway is available

in order to accommodate changes in length which result from pressure.

– Avoid mechanical stressing of the tubing line.

– Do not bend the tubing line into a radius of less than its specified minimum bending radius

of 51 mm.

– Do not twist the tubing line during installation.

– Make sure that tubing lines do not become kinked.

Mark the completed tubing connections in the hydraulic circuit diagram.



2. Becoming familiar with the commissioning procedure

Information

During practice operation and for industrial maintenance purposes, safe commissioning is

undertaken at low pressure which is then increased up to the maximum value. This is possible with

either a pressure-relief valve or a pump recirculation circuit. At low pressure, leaks can be safely

detected after device replacement, for example.

Commissioning procedure with pump recirculation circuit

1. Switch to pump recirculation by opening the shut-off valve.

2. With electro-hydraulic controls, activate the electrical 24 V DC control voltage.

3. Switch the hydraulic pump on.

4. Slowly close the shut-off valve until a circulating pressure of approximately 15 bar prevails.

Immediately set the pump back to recirculation in the event of leaks.

5. Run the sequence once and watch for leaks.

6. Fully close the shut-off valve and set the pressure limit at the pressure-relief valve of the

hydraulic power unit to the specified value.

3. Finding out about the procedure when taking measurements in the electrical circuit

Safety instructions

• Before measuring, make sure that the section of the controller in which you intend to take

measurements only works with an electrical voltage of no greater than 24 V DC!

• Measurements within sections of the controller which function with higher voltages (e.g. 230 V)

may only be performed by persons who have received appropriate training or instruction.

• Incorrect performance of this measurement is life endangering!

• Observe the safety precautions for working with electrical power!



Information

Procedure for performing measurements in the electrical circuit

1. Switch off supply power to the electrical circuit.

2. Select the desired operating mode at the multimeter (e.g. direct current measurement).

3. Connect the measuring instrument with correct polarity when measuring direct current/

direct voltage.

4. Select the largest measuring range.

5. Switch supply power to the electrical circuit back on.

6. Watch the display and switch to increasingly smaller measuring ranges step-by-step.

7. Read the value from the display after arriving at the smallest possible measuring range.

4. Double checking the controller setup

Observe the following points when commissioning the controller:

Before commissioning, make sure that all tank lines have been connected and that all couplings have

been securely fitted.

Fully close the flow control valve 1V3.

Fully open both pressure-relief valves 1V1 and 1V4.

Switch to pump recirculation by opening shut-off valve 1V2.

Switch off the 24 V DC electrical supply voltage for the flow sensors and pressure switches.

Note

You will find information on the sensors in the operating instructions.

When using the analogue output of the pressure switch, make sure it is set to between 0-10 V.

Switch the hydraulic power unit on.

Slowly close the shut-off valve 1V2. The entire pump unit delivery rate flows at low pressure through the

pressure-relief valve 1V1 to the tank.


Set the pressure at the pressure-relief valve 1V1 to 45 bar.

Perform the measurement tasks.

5. Measuring pressure and flow rate at different load pressures

Execution

Set the pressure-relief valve 1V1 to 45 bar. Set the values indicated in the table for the flow control

valve 1V3 and the pressure-relief valve 1V4. Measure the pressure and flow rate for these values.



– Set the values indicated in the table. Enter the measured pressure and flow rate values into the table.

Load case Valve specifications Pump pressure

p1 [bar]

Flow rate

q1 [l/min]

Load pressure

p2 [bar]

Flow rate

q2 [l/min]

a 1V3: open

1V4: Minimum pressure 15.8 4.14 12.4 4.22

b 1V3: open 33 4.1 30 4.18

c 1V4: Minimum pressure 43.8 4.06 3.2 0.5

d — 43.6 4.06 30 0.5

e — 40.6 4.06 25 2

f — 45 4.06 1 0

Measurement log

Notes

Fully open the flow control valve 1V3 before dismantling the controller.

Fully open the pressure-relief valves 1V1 and 1V4 before dismantling.

6. Calculating the pumping power, effective power and power loss

Information

The formula for calculating the power in the hydraulic system when using the indicated physical

units is:

600

q pP

P Power [kW]

q Flow rate [l/min]

p Pressure [bar]

Power output of the pump unit: PP

1 1P 600

q pP

PP Power output of the pump unit [kW]:

q1 Flow volume of the pump unit [l/min]

p1 Pump pressure [bar]



Effective power (output of the consuming device): PL

2 2L 600

q pP

PL Output of the consuming device [kW]

q2 Flow rate to the consuming device [l/min]

p2 Load pressure [bar]

Power loss: PV

V P LP P P

PV Power loss [kW]

a) Calculate the pumping power, effective power and power loss for the load cases a to f (see workbook 4).

Enter the values to the table.

Load case Pumping power

PP [kW]

Effective power

PL [kW]

Power loss

PV [kW]

a 0.109 0.087 0.022

b 0.226 0.209 0.017

c 0.296 0.003 0.293

d 0.295 0.025 0.27

e 0.275 0.083 0.192

f 0.305 0 0.305

Performance for the load cases a to f



b) Transfer the performance values for load cases a to f to a bar chart.

0.25

kW

P

0

0.1

0.2

0.05

0.15

0.35

a b c d e f

PP

PL

PV

PP PL PV PP PL PV PP PL PV PP PL PV PP PL PV PP PL PV

PP Pumping power

PL Effective power

PV Power loss

Performance of the system with constant displacement pump and pressure limitation with different load cases a to f

c) When is power loss PV particularly high? Give reasons for your answer.

Power loss (PV) is particularly high when the flow rate of the consuming device (q2) is low. In this case,

almost the entire delivery rate of the pump unit must discharge at maximum pressure through the

pressure-relief valve.


Contents

Exercises and worksheets: Mobile hydraulics, basic level working hydraulics (TP 801)












Exercises and worksheets: Mobile hydraulics, advanced level steering system (TP 802)






Exercises and worksheets: Mobile hydraulics, advanced level working hydraulics (TP 803)



Exercise 3-3: Remotely controlling proportional directional control valves using a hydraulic joystick __ 151







Exercise 1-1

Examining performance for a controller using constant displacement pump

and fixed pressure limitation

Learning objectives

After completing this exercise:

you will be familiar with the relationship between pressure, flow rate and power output.

you will be able to calculate the power consumption of a hydraulic system.

you will know that flow division can lead to energy losses in a hydraulic system.

you will know that when using a constant displacement pump, non-decreasing volume flow leads to

energy loss.

Problem description

The motor speed of a wheel milling cutter is controlled using a flow control valve. The rotation of the motor

is only in one direction. The load acting on the motor changes depending on the soil conditions.

Examine how different load requirements affect the energy balance of the controls.

Positional sketch

Wheel saw, © Bobcat, www.bobcat.eu


4 Name: __________________________________ Date: ____________ © Festo Didactic GmbH & Co. KG 574166

Parameters

When the hydraulic power unit is switched on, the motor will turn.

The load on the motor should be simulated using a proportional pressure-relief valve.

Project assignments

1. Set up the controller.

2. Familiarise yourself with the commissioning procedure.

3. Find out about the procedure when taking measurements in the electrical circuit.

4. Double check the controller configuration.

5. Measure the pressure and flow rate at different load pressures.

6. Calculate the power output of the pump unit; the effective power and the power loss based on the

measured values. Depict the calculated power output in the bar chart and evaluate the results.

Visual inspection

Continuous visual inspection for defects in tubing and hydraulic devices is an essential part of

hydraulic safety standards.

Work aids

Data sheets, operating instructions

Hydraulics textbook

Basics of mobile hydraulics (see attachment)


© Festo Didactic GmbH & Co. KG 574166 Name: __________________________________ Date: ____________ 5

1. Setting up the controller

1B3

0Z1

1V1

p2

1V3

1B4

45 bar

P2LS T T L L LA LAP1

60 bar

P

Tp1

1V4

1V2

P

Tq2

n

1B21A1

n

1B1

q1

A

B

Circuit diagram

Note

The pressure-relief valve 1V4 is used to set load pressures.



Quantity Labelling Designation

2 1B3, 1B4 Electronic pressure switch

2 1B1, 1B2 Flow sensor, coupled with hydraulic motor

1 1A1 Hydraulic motor

1 1V3 Flow control valve

2 1V1, 1V4 Pressure-relief valve

1 1V2 Shut-off valve

2 — 4-way manifold plate with pressure gauge

9 — Tubing line

1 0Z1 Hydraulic power unit with constant displacement pump

Equipment list

Note

You will need the following in order to perform the measurements.

• 1 power pack 24 V DC

• 2 digital multimeters

– Set up the controller.

Observe the following points when setting up the controller:

Set the pressure-relief valve for the constant displacement pump of the hydraulic power unit to a

pressure of 60 bar (6 MPa) before setting up the control.

Use the circuit diagram.

Designate the components.



pressure!




Selecting and laying tubing lines

– Select the tubing line length such that adequate leeway is available

in order to accommodate changes in length which result from pressure.

– Avoid mechanical stressing of the tubing line.

– Do not bend the tubing line into a radius of less than its specified minimum bending radius

of 51 mm.

– Do not twist the tubing line during installation.

– Make sure that tubing lines do not become kinked.

Mark the completed tubing connections in the hydraulic circuit diagram.



2. Becoming familiar with the commissioning procedure

Information

During practice operation and for industrial maintenance purposes, safe commissioning is

undertaken at low pressure which is then increased up to the maximum value. This is possible with

either a pressure-relief valve or a pump recirculation circuit. At low pressure, leaks can be safely

detected after device replacement, for example.

Commissioning procedure with pump recirculation circuit

1. Switch to pump recirculation by opening the shut-off valve.

2. With electro-hydraulic controls, activate the electrical 24 V DC control voltage.

3. Switch the hydraulic pump on.

4. Slowly close the shut-off valve until a circulating pressure of approximately 15 bar prevails.


5. Run the sequence once and watch for leaks.

6. Fully close the shut-off valve and set the pressure limit at the pressure-relief valve of the

hydraulic power unit to the specified value.

3. Finding out about the procedure when taking measurements in the electrical circuit

Safety instructions

• Before measuring, make sure that the section of the controller in which you intend to take

measurements only works with an electrical voltage of no greater than 24 V DC!

• Measurements within sections of the controller which function with higher voltages (e.g. 230 V)

may only be performed by persons who have received appropriate training or instruction.

• Incorrect performance of this measurement is life endangering!

• Observe the safety precautions for working with electrical power!



Information

Procedure for performing measurements in the electrical circuit

1. Switch off supply power to the electrical circuit.

2. Select the desired operating mode at the multimeter (e.g. direct current measurement).

3. Connect the measuring instrument with correct polarity when measuring direct current/

direct voltage.

4. Select the largest measuring range.

5. Switch supply power to the electrical circuit back on.

6. Watch the display and switch to increasingly smaller measuring ranges step-by-step.

7. Read the value from the display after arriving at the smallest possible measuring range.

4. Double checking the controller setup

Observe the following points when commissioning the controller:

Before commissioning, make sure that all tank lines have been connected and that all couplings have

been securely fitted.

Fully close the flow control valve 1V3.

Fully open both pressure-relief valves 1V1 and 1V4.

Switch to pump recirculation by opening shut-off valve 1V2.

Switch off the 24 V DC electrical supply voltage for the flow sensors and pressure switches.

Note

You will find information on the sensors in the operating instructions.

When using the analogue output of the pressure switch, make sure it is set to between 0-10 V.

Switch the hydraulic power unit on.

Slowly close the shut-off valve 1V2. The entire pump unit delivery rate flows at low pressure through the

pressure-relief valve 1V1 to the tank.


Set the pressure at the pressure-relief valve 1V1 to 45 bar.

Perform the measurement tasks.

5. Measuring pressure and flow rate at different load pressures

Execution

Set the pressure-relief valve 1V1 to 45 bar. Set the values indicated in the table for the flow control

valve 1V3 and the pressure-relief valve 1V4. Measure the pressure and flow rate for these values.



– Set the values indicated in the table. Enter the measured pressure and flow rate values into the table.

Load case Valve specifications Pump pressure

p1 [bar]

Flow rate

q1 [l/min]

Load pressure

p2 [bar]

Flow rate

q2 [l/min]

a 1V3: open

1V4: Minimum pressure

b 1V3: open 30

c 1V4: Minimum pressure 0.5

d — 30 0.5

e — 25 2

f — 1 0

Measurement log

Notes

Fully open the flow control valve 1V3 before dismantling the controller.

Fully open the pressure-relief valves 1V1 and 1V4 before dismantling.

6. Calculating the pumping power, effective power and power loss

Information

The formula for calculating the power in the hydraulic system when using the indicated physical

units is:

600

q pP

P Power [kW]

q Flow rate [l/min]

p Pressure [bar]

Power output of the pump unit: PP

1 1P 600

q pP

PP Power output of the pump unit [kW]:

q1 Flow volume of the pump unit [l/min]

p1 Pump pressure [bar]



Effective power (output of the consuming device): PL

2 2L 600

q pP

PL Output of the consuming device [kW]

q2 Flow rate to the consuming device [l/min]

p2 Load pressure [bar]

Power loss: PV

V P LP P P

PV Power loss [kW]

a) Calculate the pumping power, effective power and power loss for the load cases a to f (see workbook 4).

Enter the values to the table.

Load case Pumping power

PP [kW]

Effective power

PL [kW]

Power loss

PV [kW]

a

b

c

d

e

f

Performance for the load cases a to f



b) Transfer the performance values for load cases a to f to a bar chart.

a b c d e f

PP

PL

PV

PP PL PV PP PL PV PP PL PV PP PL PV PP PL PV PP PL PV

0.25

kW

P

0

0.1

0.2

0.05

0.15

0.35

PP Pumping power

PL Effective power

PV Power loss

Performance of the system with constant displacement pump and pressure limitation with different load cases a to f

c) When is power loss PV particularly high? Give reasons for your answer.

© Festo Didactic GmbH & Co. KG 574166 I-1

Contents

Fundamentals of mobile hydraulics

1 Introduction _____________________________________________________________________ I-5

2 Fundamentals of hydraulics ________________________________________________________ I-7

2.1 Fundamentals of pressure and flow control valves ______________________________________ I-7

2.2 Pressure drop ___________________________________________________________________ I-10

2.3 Heat generation due to pressure drop _______________________________________________ I-13

3 Closed hydraulic circuit (hydrostatic system) _________________________________________ I-15

3.1 Structure of a closed hydraulic circuit ________________________________________________ I-15

3.2 Hydraulic pumps for closed hydraulic circuits _________________________________________ I-17

3.2.1 Mechanical adjustment of hydraulic pump ____________________________________________ I-17

3.2.2 Hydraulic adjustment of hydraulic pump _____________________________________________ I-18

3.3 Feed pumps _____________________________________________________________________ I-20

3.4 Flushing valves __________________________________________________________________ I-20

3.5 Shock valves ____________________________________________________________________ I-21

4 Load-sensing systems ____________________________________________________________ I-23

4.1 Features of load-sensing systems ___________________________________________________ I-23

4.1.1 Open-centre load-sensing systems __________________________________________________ I-23

4.1.2 Closed centre load sensing systems: _________________________________________________ I-25

4.2 Energy efficiency of hydraulic pressure supply system __________________________________ I-30

4.2.1 Energy loss _____________________________________________________________________ I-30

4.2.2 Pressureless pump recirculation circuit ______________________________________________ I-32

4.2.3 Volumetric flow control in systems with a constant-displacement pump ____________________ I-34

4.2.4 Volumetric flow control in systems with a variable-displacement pump ____________________ I-36

4.2.5 Volumetric flow control in open-centre load-sensing systems _____________________________ I-38

4.2.6 Volumetric flow control in closed-centre load-sensing systems ___________________________ I-40

5 Variable-displacement pumps _____________________________________________________ I-42

5.1 Types of variable-displacement pumps _______________________________________________ I-42

5.2 Vane pump _____________________________________________________________________ I-42

5.3 Axial piston pump ________________________________________________________________ I-44

6 Two-pump system with shut-off valve _______________________________________________ I-46

6.1 Requirements for a pump system for mobile machines __________________________________ I-46

6.2 Example of a two-pump system with shut-off valve _____________________________________ I-47

I-2 © Festo Didactic GmbH & Co. KG 574166

7 Flow-dividing valves _____________________________________________________________ I-48

7.1 Synchronous running of drives _____________________________________________________ I-48

7.2 Flow divider valve (50/50 slide valve) ________________________________________________ I-48

7.3 Rotary flow divider valve __________________________________________________________ I-50

7.4 Rotary flow divider valve for pressure boost ___________________________________________ I-51

8 Valve manifolds for mobile hydraulics _______________________________________________ I-49

8.1 Structure of valve manifolds _______________________________________________________ I-53

8.2 Circuit symbols for proportional directional control valves in valve modules _________________ I-55

8.3 Structure of valve modules ________________________________________________________ I-56

8.4 Valve slides of proportional directional control valves ___________________________________ I-57

8.4.1 Design of valve slides _____________________________________________________________ I-57

8.4.2 Influence of control notches on flow characteristics ____________________________________ I-58

8.5 Input module of a valve manifold ___________________________________________________ I-59

8.5.1 Structure of an input module _______________________________________________________ I-59

8.5.2 Input module in conjunction with an open-centre valve module ___________________________ I-60

8.5.3 Input module in conjunction with a closed-centre valve module ___________________________ I-61

8.6 Shock and replenishing valve ______________________________________________________ I-62

9 Circuits with open-centre valves ____________________________________________________ I-64

9.1 Open-centre valves _______________________________________________________________ I-64

9.2 Structure of an open-centre 6/3-way valve ____________________________________________ I-66

9.3 Parallel circuit ___________________________________________________________________ I-69

9.4 Tandem circuit __________________________________________________________________ I-70

9.5 Series circuit ____________________________________________________________________ I-71

10 Non-load-dependent volumetric flow control with proportional valves ____________________ I-72

10.1 Proportional flow control valve _____________________________________________________ I-72

10.2 Upstream pressure balance valve ___________________________________________________ I-74

10.3 Downstream pressure balance valve _________________________________________________ I-78

11 Holding and safe lowering of loads _________________________________________________ I-82

11.1 Example of application ____________________________________________________________ I-82

11.2 Piloted non-return valve ___________________________________________________________ I-83

11.3 Pressure-relief valve ______________________________________________________________ I-84

11.4 Counterbalance valve _____________________________________________________________ I-85

12 Hydraulic piloting _______________________________________________________________ I-88

12.1 Hydraulic piloting with a joystick ____________________________________________________ I-88

13.2 Hydraulic joystick (manually-operated piloting) ________________________________________ I-88

13.3 Electronic joystick (electrohydraulic piloting) __________________________________________ I-90


13 Prioritisation of load devices ______________________________________________________ I-92

13.1 Necessity for prioritisation of load devices ____________________________________________ I-92

13.2 Pressure sequence valve __________________________________________________________ I-92

13.3 Prioritisation through circuit design _________________________________________________ I-93

13.4 Directional control valve with prioritisation ___________________________________________ I-94

13.5 Static priority valve _______________________________________________________________ I-94

13.6 Dynamic priority valve ____________________________________________________________ I-95

13.7 3-way flow control valve ___________________________________________________________ I-96

14 Hydrostatic steering _____________________________________________________________ I-98

14.1 Structure and features of hydrostatic steering _________________________________________ I-98

14.2 Structure of steering valves ________________________________________________________ I-98

14.2.1 Rotary slide valve and bushing _____________________________________________________ I-99

14.2.2 Metering pump (Orbitrol pump) ____________________________________________________ I-100

14.3 Types of steering valves __________________________________________________________ I-101

14.3.1 Open-centre steering valves ______________________________________________________ I-101

14.3.2 Closed-centre steering valves _____________________________________________________ I-102

14.3.3 Load-sensing steering valves ______________________________________________________ I-103

14.3.4 Reaction and non-reaction steering valves ___________________________________________ I-103

14.4 Types of steering systems ________________________________________________________ I-104

14.4.1 Ackermann steering system with steering knuckles ____________________________________ I-105

14.4.2 Articulated steering system _______________________________________________________ I-105

Picture credits ________________________________________________________________________ I-107



1 Introduction

Example of a vehicle with mobile hydraulics

There are a number of special conditions which occur in mobile hydraulics but not in industrial hydraulics:

No regular working cycle

In industrial hydraulic systems, the force acting on the drive is normally constant. With mobile systems,

on the other hand, the operative force is extremely variable. For hydraulic applications with variable

force and speed, the use of a constant-displacement pump and a maximum pressure safety valve is not

an economic solution.·

Generally no external energy supply

Harsh environmental conditions

These may include large temperature differences, dust and impacts.

Limited installation space

Limited weight

From the above we derive the requirements for mobile hydraulic systems:

Efficiency in energy consumption

The most important consideration in mobile systems is efficiency: As mobile machines generally move

independently from any power source, the power supply is limited. In most cases, the only power

source is an internal combustion engine with a limited fuel supply.

Compact design

The individual components of mobile machines, such as tanks, pumps, motors, cylinders and valves

should be kept as small and light as possible. In order to achieve the desired performance with small

components, it is necessary to increase the pressure. Higher pressure in turn demands valves with close

tolerances in order to minimise leakage losses. Close-tolerance valves and the high performance

density make it necessary to pay more attention to filtering and cooling the hydraulic fluid.

Robust design

The components are subjected to wide temperature fluctuations. Moreover, the drives are frequently

subject to wide and rapid fluctuations in force. External drives and supply-line hoses are directly

exposed to dirt and collisions, for example with excavated material. This means that the hydraulic

components must be of robust design.

1 Introduction


The following hydraulic systems are used in mobile machines:

Closed hydrostatic transmission, e.g. for travel operation·

Working hydraulics

Steering system

Braking system

Two types of hydraulic circuits are used in mobile machines

Open circuit

In an open circuit, a pump delivers fluid from a tank to load devices. From the load devices, the fluid

then flows back to the tank. Open circuits are used above all for working hydraulics.

Closed circuit

In a closed circuit, a pump delivers fluid to load devices. There are generally no flow control or

directional control valves between the pump and the load devices. From the load devices, the fluid then

flows back directly to the pump..

Often the pump acts as a controller for both the volume and direction of the flow of fluid. Closed circuits

are used mostly for travel drives

There are of course also combinations of the two types of circuit within one machine. In these cases, the

vehicle engine drives several pumps. The main pump in this case is the pump for the closed drive circuit,

while the auxiliary pumps operate with open circuits and supply the working hydraulic systems.

Documents

Mobile Hydraulics - Festo Didactic