Festo TP 800 User Manual

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Mobile Hydraulics

Workbook

TP 800

With CD-ROM

Festo Didactic

574166 en

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

+49 711 3467-0 www.festo-didactic.com +49 711 34754-88500 did@de.festo.com

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.

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 Exercise 1-2: Examining performance for a controller using constant displacement pump 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

III

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)

Exercise 1-1: Examining performance for a controller using constant displacement pump and fixed pressure limitation _____________________________________________________ 3 Exercise 1-2: Examining performance for a controller using constant displacement pump 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 worksheets: 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

Exercises and worksheets: 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 directional control 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

IV © Festo Didactic 574166

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

V

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

VI © Festo Didactic 574166

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

VII

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.

VIII

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.

IX

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 tips, feedback or suggestions for improving this workbook?

If so, please send us an e-mail at did@de.festo.com. The authors and Festo Didactic look forward to your feedback.

X © Festo Didactic 574166

Introduction

This workbook is part of the training system for automation technology from Festo Didactic SE. 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.).

XI

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.

XII © Festo Didactic 574166

• 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.

XIII

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 Fundamentals of hydraulics and electrohydraulics

Workbooks Mobile hydraulics (TP 800)

Set of posters Hydraulics

Simulation programme FluidSIM® Hydraulic

TP 810 Diagnostic system FluidLab® M

Digital training programme

Overview of media for training package TP 800

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

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

XIV © Festo Didactic 574166

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 opencentre 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.

XV

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.

XVI © Festo Didactic 574166

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

To know that proportional directional control valves restrict inflow

Allocation of learning objectives to exercises

Mobile hydraulics: Basic level working hydraulics (TP 801)

Learning objective

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

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

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

system.

To know that when using a constant displacement pump, nondecreasing 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.

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.

•

XVII

To be able to describe the advantages and disadvantages of these

Learning objective

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

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 6/3way proportional valves work.

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. •

•

XVIII © Festo Didactic 574166

To know the relationship between load changes and speed changes when

Mobile hydraulics: Advanced level working hydraulics (TP 803)

Learning objective

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

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

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

To know the power-relevant advantages of hydraulic systems with loadsensing-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.

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.

•

XIX

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

XX © Festo Didactic 574166

T2P1P2

BT1

A

T

A

P

B1A1

B2A2

A B

P

T

X

T

P

0.55 MPa

P

T

X

0.55 MPa

Graphic symbols, equipment set

Component Graphic symbol

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

3-way pressure regulator

Shut-off valve

Double non-return valve, delockable

Flow control valve

Pressure-relief valve

Pressure balance for open-centre load-sensing

XXI

p

2

RD (1)

BK1 (4), BK2 (5), WH (2)

BU (3)

p

U

SP1 SP2

0V (BU)

q

24V (RD)

0 – 10V (BK)

1 0 2

TP

X

(1:3)

P

T

Component Graphic symbol

Electronic pressure switch ISO 1219-1 EN 60617-7

Flow sensor ISO 1219-1 EN 60617-7

Hydraulic motor

Diaphragm accumulator with shutoff block

Non-return valve, opening pressure:

0.6 MPa

Delockable counter balance valve (overcentre valve)

T-distributor

XXII © Festo Didactic 574166

B

A2A1

A1.2

A1.1 A2.1 A2.2

Component Graphic symbol

4-way manifold plate, with pressure gauge

Shuttle valve

Cylinder load simulator (loading unit)

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

Designation Order number Quantity

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

XXIII

BA

TP

L R

P ET

T

B1

B2

A1

A2

Graphic symbols, equipment set

Component Graphic symbol

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

Steering valve (Orbitrol)

Shock and replenishing manifold

4-way return header, unpressurised

Tubing line for unpressurised return

XXIV © Festo Didactic 574166

A B

X

A

P

35 kPa

A

P

X

35 kPa

X

P

A

0.55 MPa

A

P

X

0.55 MPa

T

P

D (X1.2)

A1

B1

LS

D (X2.2)

A2

B2

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

Designation Order number Quantity

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

Graphic symbols, equipment set

Component Graphic symbol

Flow control valve

Pressure balance, downstream

Pressure balance, upstream

Load-sensing control block

XXV

X1.1

T

P

X1.2 X2.1 X2.2

Component Graphic symbol

Tubing line for unpressurised return

T-distributor

Pilot controller (joystick), 2x2-channel

XXVI © Festo Didactic 574166

Allocation of components to exercises

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

Component

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

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

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

1 1 1 1 1 1 2

Shuttle valve 1

Cylinder load simulator (loading unit) 1 1 1 1

Required accessories

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)

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

1 1 1 1 1 1 1 1 1

XXVII

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

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

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

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.

Required accessories

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

XXVIII © Festo Didactic 574166

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

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

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

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

Required accessories

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

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

Tubing line 10 10 9 8 9 15 16

1 1 1 1 1 1 1

XXIX

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: 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.

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:

• Data sheets

• Illustrations

• Operating instructions

XXXI

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.

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.

Operating instructions

Operating instructions are provided for various components included in the training package. These instructions are helpful when using and commissioning the components.

Contents

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 Exercise 1-2: Examining performance for a controller using constant displacement pump 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

1

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

3

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)

1B3

0Z1

1V1

p

2

1V3

1B4

45 bar

P2LS T T L L LAL

A

P1

60 bar

P

T

p

1

1V4

1V2

P

T

q

2

n

1B2

1A1

n

1B1

q

1

A

B

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

1. Setting up the controller

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.

5

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

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.

• 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.

• 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.

Exercise 2-5 – Designing a steering system for centre-pivot steering

1. Designing the circuit plan for the control unit of the centre-pivot steering

– Design the hydraulic circuit diagram for the pivot-centre steering. The forces of the two steering cylinder

should accumulate while steering. Also complete the positional sketch and the hydraulic circuit diagram.

Positional sketch

125

Exercise 2-5 – Designing a steering system for centre-pivot steering

Circuit diagram

Quantity Labelling Designation

1 1A1, 1A2 Cylinder load simulator

1 1V2 Steering valve (Orbitrol), Non-reaction

1 1V1 Shut-off valve

2 — T-distributor

2 — 4-way manifold plate with pressure gauge

1 — 4-way return header, unpressurised

1 — Tubing line for unpressurised return

9 — Tubing line

1 — Hydraulic power unit with constant displacement pump

Equipment list

1B3

0Z1

1V1

p

2

1V3

1B4

45 bar

P2LS T T L L LAL

A

P1

60 bar

P

T

p

1

1V4

1V2

P

T

q

2

n

1B2

1A1

n

1B1

q

1

A

B

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

1. Setting up the controller

Circuit diagram

Note

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

5

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

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.

• 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.

• 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 Fundamentals of hydraulics

2.1 Fundamentals of pressure and flow control valves

Knowledge of the fundamentals of pressure and flow control valves is important for an understanding of the function and mode of operation of mobile machines.

Below is an illustration of a mobile machine. The speed of the cylinder drive is varied by a throttle valve used as a flow control valve. For a study of the system, two pressure values are important: the pressure upstream of the throttle valve and the pressure

p

downstream of the throttle valve.

2

p

1

Schematic representation of a mobile system with the following settings: Pressure relief valve: 275 bar (27.5 MPa) Opening pressure of pressure relief valve: 250 bar (25 MPa) Pump delivery rate: 100 l/min

1. What causes the pressure p The pressure p

is governed by the weight and position of the load and the piston diameter of the drive.

2

to rise or fall?

2

2. What is the pressure difference between p The difference between the pressures p

and p2 when the throttle valve is fully open?

1

and p2 is governed by the resistance in the throttle valve. When

1

the throttle valve is fully open, the hydraulic resistance is very low. The following applies as a first approximation: p

= p2.

1

I-7

2 Fundamentals of hydraulics

3. Does the drive speed change when the throttle valve is partially closed and the pressure p1 rises to 200 bar (20 MPa)? The drive speed depends on the volumetric flow q. As long as the pressure p opening pressure of the pressure relief valve, the full volumetric flow will continue to flow to the drive. The drive speed remains the same.

4. How high is the pressure p

if the drive advances at half speed?

1

If the drive advances at half speed, this means that only half the required volumetric flow is flowing to the drive. The other half is forced to flow via the pressure relief valve to the tank. The pressure/volumetric flow curve shows that with a volumetric flow of 50 l/min. (corresponding to half the pump delivery rate) a pressure of approx. 260 bar (26 MPa). The pressure (26 MPa).

is not higher than the

1

p

is therefore 260 bar

1

Pressure/volumetric flow curve for pressure relief valve

12 Hydraulic piloting

When the joystick is not actuated, ports X1 and X2 are connected to the tank. The hand lever operates via a rocker arm to actuate one of the two pressure-reducing valves. These control the pressure at the associated pilot port X1 or X2 proportionally to the deflection of the hand lever. This pressure is also fed to the slide of the piloted proportional directional control valve, which is pushed proportionally against the centring spring. At the same time, the hydraulic fluid displaced by the valve slide is discharged via the other pressure-reducing valve. The pilot pressure is approx. 15 bar (1.5 MPa). This means that, when the pressure at the pilot port changes, so does the position of the slide in the proportional directional control valve. Steplessly.

The illustration below shows the basic version of a joystick, which can be moved in only two directions – to the left or right. There are also versions which support movement in four directions: left, right, forward and reverse.

Joystick in conjunction with a load-sensing control block – schematic representation

I-89

5 Centring spring

10 Electronics

12 Hydraulic piloting

12.3 Electronic joystick (electrohydraulic piloting)

Electrohydraulic piloting offers the advantage that it is not necessary to route hydraulic lines to the hand lever of the joystick. The control slide of the directional control valve is positioned by the directly-attached pilot stage. The hand lever of the electronic joystick can also be connected to the directional control valve via a bus system. This means that wiring costs are low. It is also possible to arrange for the setpoint signal to be processed within a safety concept.

The illustration shows the structure of a valve module with manual operation and an electronic actuating system.

1 Piloting 2 Pilot fluid supply 3 Valve module 4 Hand lever

Valve module with manual operation and electronic actuating system – cutaway view Original component SAUER-DANFOSS, www.sauer-danfoss.com

6 Control slide 7 Displacement encoder 8 Valve with Open neutral position 9 Valve with closed neutral position

The illustration below shows in schematic form the structure and mode of operation of an electronic joystick with electronic piloting of the proportional directional control valve.

14 Hydrostatic steering

Articulated steering systems with steering cylinder installed in different positions - left: two steering cylinders; centre: steering cylinder on left; right: steering cylinder on right

Vehicles with articulated steering, such as the one shown below, are distinguished by high manoeuvrability within confined spaces. The steering does not change the distance between the wheels and the load (bucket). Articulated steering is the preferred choice for construction-industry machines.

Picture credits

The image rights are designated in the captions.

We thank the following companies for their permission to reproduce copyright images: BONDIOLI & PAVESI, Bondioli & Pavesi GmbH, D-64521 Groß-Gerau DEUTZ-FAHR, SAME DEUTZ-FAHR DEUTSCHLAND GmbH, D-89415 Lauingen Hako, Hako-Werke GmbH, D-23843 Oldesloe LIEBHERR, Liebherr-Hydraulikbagger GmbH, D-88457 Kirchdorf Linde Material Handling GmbH, Linde Hydraulics, D-63741 Aschaffenburg Rudolph - Bau-Forst-Landmaschinentechnik, D-39615 Krüden SAUER-DANFOSS, Sauer-Danfoss GmbH & Co. OHG, D-63073 Offenbach/Main WACKER NEUSON, Wacker Neuson Vertrieb Europa GmbH & Co. KG, D-80809 München

I-107

Festo TP 800 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

2 Fundamentals of hydraulics