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    Fundamentals of 

    Electrohydraulics

    Collection of 

    Transparencies

    T A P B

    T A P B

    A

    a b

    B

    P T

    a

    a

    b

    b

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    Order no.: 095051

    Designation: E.-HYDR-FOLIEN.

    Description: D:OT-TP601-GB

    Edition: 07/2001

    Author: Dieter Scholz

    Graphics: Doris Schwarzenberger

    L t 18 07 2001 B t i H b

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    Foreword

    This set of overhead transparencies has been designed for use with the basic level

    of the technology package TP600 “Electrohydraulics”. The set of overhead

    transparencies and the technology package form part of the Learning System for

    Automation from Festo Didactic GmbH & Co.

    The 30 transparencies in this set have been optimised from the didactic and

    methodological points of view. Each transparency is accompanied by a short text

    which provides the trainer with a quick overview of the training contents of the

    transparency concerned.

      Basic principles of electrohydraulics

      Function and use of electrohydraulic components

     

    Basic principles of electrical engineering

      Production and interpretation of standard hydraulic and electrical circuit

    diagrams

    The text sheet includes a complete illustration of the transparency, in certain cases

    with additional explanations and legends which the trainer can enter on the

    transparency in the course of a training session.

    The advantages of this concept are:

      The trainer can add to the transparencies step by step in the course of a training

    session.

      The trainer is thus able to create a lively and interesting atmosphere.

      The provision of accompanying text means less preparation work for the trainer.

    The enclosed CD-ROM contains the entire overhead transparencies and

    accompanying text of this edition in an electronically presentable form in the files

    „Electrohydraulics _transparencies.pdf“ and „Electrohydraulics _text.pdf“. In

    addition to the screen presentation, which can be made in any order, the contents

    can be printed out and text and graphics can be used for your own training

    preparations, insofar as the functionality of the required Adobe®

     Acrobat®

     Reader

    it thi Thi f l di t ib t bl ft i il bl th CD ROM i th

    Training contents

    New!

    Electronic presentation

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    Contents

    Electrohydraulic press _______________________________________ Transparency 1

    Schematic layout of an electrohydraulic installation ______________ Transparency 2

    Electrical power supply unit __________________________________ Transparency 3

    Electrical circuit ____________________________________________ Transparency 4

    Measuring circuits __________________________________________ Transparency 5Ohm’s law _________________________________________________ Transparency 6

    Rectifiers __________________________________________________ Transparency 7

    Analogue, digital and binary __________________________________ Transparency 8

    Momentary and sustained contact switches _____________________ Transparency 9

    N/O, N/C and changeover contacts ___________________________ Transparency 10

    Limit switches_____________________________________________ Transparency 11

    Proximity switches _________________________________________ Transparency 12

    Solenoid (electromagnet) ___________________________________ Transparency 13

    Electrohydraulic converters (solenoid valves)___________________ Transparency 14

    Dry solenoids – wet solenoids________________________________ Transparency 15

    Solenoid valve connections__________________________________ Transparency 16

    Relays and contactors ______________________________________ Transparency 17

    Direct activation – indirect activation __________________________ Transparency 18

    Signal inversion ___________________________________________ Transparency 19

    Latching__________________________________________________ Transparency 20Circuit diagram ____________________________________________ Transparency 21

    Hydraulic power pack_______________________________________ Transparency 22

    Hydraulic circuit ___________________________________________ Transparency 23

    Electrical power – hydraulic power ____________________________ Transparency 24

    Power losses______________________________________________ Transparency 25

    Pressure switches__________________________________________ Transparency 26

    4/3-way solenoid valve _____________________________________ Transparency 27

    4/3-way solenoid valve, piloted ______________________________ Transparency 28

    Electrical safety____________________________________________ Transparency 29

    Hydraulic safety ___________________________________________ Transparency 30

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    1

    Electrohydraulic press

      Motor with hydraulic pump

      Control panel

     

    Valve manifold  Cylinder

    The hydraulic press is controlled via the electrical control panel.

    Electrical signals are used to activate the valves in the hydraulic installation.

    The electrohydraulic press is used to form rectangular troughs.

    Control pane

    Motor withhydraulic pump

    Valve manifold

    Actuator(cylinder)

    Function units

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    © Festo Didactic GmbH & Co. TP 601, 01Transparency

    Electrohydraulic press

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    2

    Schematic layout of an electrohydraulic installation

    Division of installation into signal control section and hydraulic power section.

    Input and processing of electrical signals.

    Solenoid valves form the interface between the electrical signal control section and

    the hydraulic power section.

    Controls the flow of hydraulic fluid by means of solenoid valves. Actuators convert

    hydraulic energy into motions.

         

         

    Signal control section

    Signalinput

    Hydrauliccylinder

    Solenoidvalve

    Hydraulicpowersupply(conversion)

    Powersupply

    Signalprocessing 

    Power section

              

    Signal control section

    Hydraulic power section

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    © Festo Didactic GmbH & Co. TP 601, 02Transparency

    Schematic layout of an electrohydraulic installation

    Signal control section

    Power section

              

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    3

    Electrical power supply unit

    Connection to mains supply.

    Supplies signal control section with specified or maximum voltage and currentvalues.

      Voltage transformation

      Rectification

      Smoothing

      Stabilisation

      Fuse protection

    In mobile hydraulic systems, rechargeable battery systems or generators are used

    as a power supply for the signal control section.

    230VAC

    24V

    DC

    TR

    50 °C

    G C T T

    Transformer Rectifier   Smoothing Stabilisation   Fuse

    Functions in

    power supply unit

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    © Festo Didactic GmbH & Co. TP 601, 03Transparency

    Electrical power supply unit

    230VAC

    24VDC

    TR G C T T

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    4

    Electrical circuit

    A circuit consists of at least a power source, a load device and connecting lines.

    Electrical current will flow only in a closed circuit.

    Electrical current flows from the positive terminal of the power supply to the

    negative terminal.

    Closed circuit without power supply.

    Introduction of a power supply to complete the circuit.

    A B

    +

    Technical direction

    of current flow

    Figure A

    Figure B

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    © Festo Didactic GmbH & Co. TP 601, 04Transparency

    Electrical circuit

    A B

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    5

    Measuring circuits

    The voltage drop across a load device is measured in parallel with the device.

    Electrical current is measured in series.

    ++

    Voltage measurement Current measurement

    Voltage measurement

    Current measurement

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    © Festo Didactic GmbH & Co. TP 601, 05Transparency

    Measuring circuits

    ++

    --

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    6

    Ohm’s law

    Describes the relationship between current (I), voltage (V) and resistance (R).

    With ohmic resistances, the current rises in linear proportion to the voltage.

    The value pairs for a constant resistance lie on a straight line. The current I is

    proportional to the voltage V.

    Mathematical formula for Ohm’s law: V = R • I

    I = V : R

    +

    R

    A

    2.0

    1.5

    1.0

    0.5

    0100 20

    V

        I

    30 40V

    10 V

    0.5 A

    0.33 A

    Voltage V

    20 V

    1.0 A

    0.66 A

    30 V

    1.5 A

    1.0 A

    40 V

    2.0 A

    1.33 A

    A

    V

    V = R • I

    I =RV

    Resistance R

    Relay

    Solenoid coil

    Ohm’s law

    Graph

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    © Festo Didactic GmbH & Co. TP 601, 06Transparency

    Ohm’s law

    +R

    -

    A

    2.0

    1.5

    1.0

    0.5

    0100 20

    V

        I

    30 40V

    Resistance R 10 V

    Voltage V

    20 V 30 V 40 V

    A

    V

    Relay

    Solenoid coil

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    7

    Rectifiers

    Rectifiers convert AC to DC.

    Diodes are conductive in only one direction.

    The polarity of the negative half-wave of the alternating voltage is reversed.

    The pulsating voltage is smoothed using a capacitor and filters (reactance coil,

    resistor).

    ~

    =

           V       V

    t

           V

    tt

    C R

    L

    Diodes

    Voltage

    retification

    Voltage

    smoothing

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    © Festo Didactic GmbH & Co.   TP 601, 07Transparency

    Rectifiers

    ~

    =

           V       V

    t

           V

    tt

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    8

     Analogue, digital and binary 

    Analogue values describe continuous functions, such as the continuous filling of a

    bucket of water.

    Digital values describe integer parts of a maximum value. A dice, for example, shows

    one of six possible numbers.

    Binary values are a special form of digital values. They can assume only two values,

    such as in the case of a switch, which can only be on or off.

    On 1

        V   a    l   u   e

    +

    1

    6

    5

    4

    3

    2

    0    V   o    l   u   m   e    V

    Filling time t Experiments with dice

        L    i   g    h   t

    Time tSwitchingtime point

    Off 0

    full

    half-full

    empty

    Analogue values

    Digital values

    Binary values

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    © Festo Didactic GmbH & Co. TP 601, 08Transparency

     Analogue, digital and binary

    +

    -

    Experiments with dice Time t

         V    o 

          l     u     m    e 

         V

         V    a 

          l     u     e 

         L      i    g        h     t 

    Filling time t

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    9

    Momentary and sustained contact switches

    Actuation of contacts.

    A momentary contact switch has a “rest position” and an “actuated position”.

    A sustained contact switch has two detents. It thus has two rest positions.

    Momentary and sustained switches can close or open current paths or switch from

    one current path to another.

    3 3

    4 4

    Momentary contact switch

    Sustained contact switch

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    © Festo Didactic GmbH & Co. TP 601, Transparency 09

    Momentary and sustained contact switches

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    10

    N/O, N/C and changeover contacts

    Contact normally open in rest position.

    Example: Momentary-contact switch

    N/O and N/C contacts in a single housing; one contact is open while the other is

    closed.

    The designations of the switch contacts are governed by the European standard

    EN 50012.

    Connection(N/C contact)

    42

    1

    3 1

    4 2

    Connection(N/O contact)

    Switch elements

    N/O

    N/C

    Changeover contact

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    © Festo Didactic GmbH & Co. TP 601, 10Transparency

    N/O, N/C and changeover contacts

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    11

    Limit switches

    Determining the position of a positioning slide.

    Electrical contacts are actuated when a defined intermediate or end position is

    reached.

    Limit switches can be connected up as N/O, N/C or changeover contacts.

    Switch leverStem (insulated)

    Contact

    Snap-actionmechanism

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    © Festo Didactic GmbH & Co. TP 601, 11Transparency

    Limit switches

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    12

    Proximity switches

    Signal is generated by the presence of any material with good conductivity in an

    oscillating magnetic field.

    Signal is also generated by all insulators with high dielectric constants in an

    electrical field.

    Signal is generated when light barriers are interrupted or when light is reflected

    back to an optical sensor.

    Signal is generated by magnets whose fields close the built-in contacts in the switch.

    Magnet

    Metal

    MetalorInsulator

    reflectivecompo-nent

    inductive

    capacitive

    optical   magnetic

    Reed switch

    Inductive

    Capacitive

    Optical

    Reed switches

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    © Festo Didactic GmbH & Co. TP 601, 12Transparency

    Proximity switches

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    13

    Solenoid (electromagnet)

    A magnetic field with concentric field lines is created around a conductor carrying an

    electrical current.

    A coil carrying an electrical current develops a uniform magnetic field in its axial

    direction due to the overlapping of field lines.

    By appropriate alignment of elementary magnets, an iron core can be made into a

    switchable electromagnet.

    +

    Field around

    a conductor

    Coil

    Coil

    Iron core

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    © Festo Didactic GmbH & Co. TP 601, 13Transparency

    Solenoid (electromagnet)

    +

    -

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    14

    Electrohydraulic converters (solenoid valves)

    Convert electrical signals into hydraulic switching operations.

    The switching armature is drawn into the coil, which acts as a magnet.

    This produces a displacement of the actuating piston in the hydraulic 4/2-way valve.

    A B

    P T

    Switching armature

    4/2-way solenoid valve

    BT A P L

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    © Festo Didactic GmbH & Co. TP 601, 14Transparency

    Electrohydraulic converters (solenoid valves)

    A B

    P T

    15

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    15

    Dry solenoids – wet solenoids

    The solenoid is separated from the hydraulic fluid; a seal is required on the stem.

      Simple construction

    The armature chamber of the solenoid is filled with hydraulic fluid, the solenoid

    operates in oil.

      Low friction

      Little abrasion

     

    Good heat dissipation  Long service life

    seal

    Dry solenoid Wet solenoid

    Dry solenoid

    Advantage

    Wet solenoid

    Advantages

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    © Festo Didactic GmbH & Co. TP 601, 15Transparency

    Dry solenoid Wet solenoid

    16

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    16

    Solenoid valve connections

      Solenoid with plug base

      Cable with connector socket

    Electrical signals are transmitted via standard connectors.

      Reliable alignment of connections

      Connections can be attached and detached quickly

      Protected against dust and water

    2

    1

    3

    Protective earth connection

    Plug base

    Electricalconnections

    Connector components

    Advantages

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    © Festo Didactic GmbH & Co. TP 601, 16Transparency

    Solenoid valve connections

    2

    1

    3

    17

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    17

    Relays and contactors

    Switches which are actuated and held in their actuated positions

    electromagnetically.

    Used to separate control and power circuits.

      Hinged-armature design

      Single-break contacts

      Used for logic gating of signals

      (generally) changeover contacts

    Each main contact is of double-break type (contacts used as main contacts),suitable for

      all power ratings from small to very large

      only N/O and N/C contacts

    +

    +

    Contacts

    Return spring

    Return spring

    Contacts   Coil

    Coil

    Iron core

    Armature

    Hinged-armature solenoid Plunger-armature solenoid

    Definition

    Special feature

    of relays

    Special featureof contactors

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    © Festo Didactic GmbH & Co. TP 601, 17Transparency

    Relays and contactors

    +

    +-

    -

    18

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    8

    Direct activation – indirect activation

    Connection of a solenoid valve via a switch (Fig. A).

    Connection of a solenoid valve via a relay (Fig. B).

      Separation of control and power circuits

      The current passing through switch S1 (Fig. B) is lower, and the service life of the

    switch is significantly greater.

      A B

    24 V

    0 V

    1 224 V

    0 V

    S1 S1 K1

    Y1 K1 Y1

    1

    3 3 3

    4 4 4

    Direct activation

    Indirect activation

    Advantage of 

    indirect activation

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    24 V

    0 V

    1 2

    © Festo Didactic GmbH & Co. TP 601, 18Transparency

    Indirect activationDirect activation

    24 V

    0 V

    1

    19

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    Signal inversion

    The output signal is inversely proportional to the input signal.

    Signal inversion at relay K1.

    Signal inversion at switch S1.

    The switching elements are shown under zero-voltage conditions.

    24 V

    0 V

    1 2

    S1 K1

    0

    10

    1

    Y1

    0

    1

    B

    S1 K1

    K1 Y1

    31

    42

    24 V

    0 V

    1 2

    S1 K1

    1

    00

    1

    Y1

    0

    1

    A

    S1 K1

    K1 Y1

    3 1

    4 2

    Figure A

    Figure B

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    24 V

    0 V

    1 2

    S1 K1

    0

    1

     Y1

    B

    S1 K1

    K1 Y1

    31

    42

    24 V

    0 V

    1 2

    © Festo Didactic GmbH & Co. TP 601, 19Transparency

    Signal inversion

    S1 K1

    0

    1

     Y1

    A

    S1 K1

    K1 Y1

    3 1

    4 2

    20

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    Latching 

    Latching only with indirect activation.

    Actuation of switch S1: Relay K1 reverses holding the current path of K1 closed.

    The actuation of switch S2 interrupts the latched current path.

    K1 K13 3

    4 4

    24 V

    0 V

    1 2 3

    S1

    K1 Y1

    3

    4

    S21

    2

    S1 S2

    0 0

    K1 & Y1

    0

    1

    0

    1

    0 0

    1 1

    1

    dominant on

    1

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    © Festo Didactic GmbH & Co. TP 601, 20Transparency

    Latching 

    K1 K13 3

    4 4

    24 V

    0 V

    1 2 3

    S1

    K1 Y1

    3

    4

    S21

    2

    S1 S2

    0

    K1 & Y1

    0

    1

    0

    1

    0

    1

    1

    21

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    Circuit diagram

    Lines of potential with constant voltage are drawn horizontally.

    Current paths are drawn vertically and numbered consecutively.

    Circuit symbols are shown in the direction of current flow.

    Switching elements are generally shown under zero-voltage conditions.

    Latching to guard against sticking of relay contacts in current paths 6 and 7.

    K2

    3

    4S2

    K2

    3

    4

    A2

    A1

    K1

    3

    4S1

    S0

    K1 Y1 Y2

    3

    3

    4

    4

    K2 K11 1

    2 2

    A2

    A1

    K1 K2

    3 3

    4 4

    24 V

    0 V

    1

    2 3 4 5 6 7

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    © Festo Didactic GmbH & Co. TP 601, 21Transparency

    Circuit diagram

    K2 3

    4

    S2

    K2

    3

    4

    A2

    A1

    K1 3

    4

    S1

    S0

    K1 Y1 Y2

    3

    3

    4

    4

    K2 K11 1

    2 2

    A2

    A1

    K1 K23 3

    4 4

    22

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    Hydraulic power pack 

    Hydraulic power pack for use in stationary hydraulic systems.

    Power is delivered via the pressure medium using a pump and drive motor.

    The pack incorporates devices to remove air, water and solid particles from the

    hydraulic fluid.

    Baffle plate

    Pressure relief valve(safety valve)

    Hydraulic pump

    Suction pipe

    Suction filter

    Return line

    Air filter

    Filler filter

    Fluid level indicator

    Cleaning aperture

    Drain screw

    Pressure lineElectric motor n = 1500 rpm

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    © Festo Didactic GmbH & Co. TP 601, 22Transparency

    Hydraulic power pack 

    23

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    Hydraulic circuit

    Hydraulic systems consist of open or closed circuits.

    Hydraulic fluid is used as an energy carrier.

    This energy is output via cylinders and motors.

    Relieved hydraulic fluid is returned to the tank or hydraulic pump.

    Hydraulicmotor

    Motor

    Filter

    Motor

    Hydraulic cylinder

    Electrohydraulicpower valve

    Safetyvalve

    Safetyvalve

    Hydraulicpump

    Returnline

    Safety valve

    Feed pump(top-up forleakage losses)

    Hydraulic pump

    open   closed

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    © Festo Didactic GmbH & Co. TP 601, 23Transparency

    Hydraulic circuit

    open closed

    24

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    Electrical power – hydraulic power 

    Driven by electric current on the basis of a potential difference.

    Electrical power is the product of voltage and current

    Pelectr. = V • I (unit: watts).

    Driven via fluid flow on the basis of a pressure difference.

    Hydraulic power is the product of pressure and flow rate

    Phydr. = p • Q (unit: watts).

    Electric motor

    +

    P = • Ielectr. P = p • qhydr.

    Current I

        V   o    l   t   a   g   e

        V

        P   r   e   s   s   u   r   e

       p

    Flowrate q

    Gear motor

    Electric motor

    Hydraulic motor

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    © Festo Didactic GmbH & Co. TP 601, 24Transparency

    Electrical power Hydraulic power  

    +

    -

    25

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    Power losses

      Frictional losses

      Magnetic losses

     

    Frictional losses  Volumetric losses

      Pressure losses dp

      Power losses expressed by P = dp • Q 

      Frictional losses

      Volumetric losses

    P = p • qhydr. loss  

    Frictional andvolumetric losses

    Frictional andpressure losses

    Frictional,volumetric andmagnetic losses

        P   o   w   e   r    l   o   s   s   e   s

    Efficiency of electric motors

    Efficiency of hydraulic pump

    Valves, piping, tubing

    Hydraulic motors

    and cylinders

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    © Festo Didactic GmbH & Co. TP 601, 25Transparency

    Power losses

    26

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    Pressure switches

    Actuation of electrical contacts when a defined minimum pressure is reached.

    The minimum pressure (switching point) can be varied by means of an adjustable

    spring.

    Example shows switching at approx. 4 bar with rising or falling pressure.

    Generally connected up in practice as a changeover contact.

    Hysteresis2

    3

    1

    1

    2 3

    4 bar

    pp

    a

    a/c

    b

    c

    b

    Switching point with rising pressure

    Switching point with falling pressure

    Symbolic representationin electrical circuit diagram

    Symbolic representationin hydraulic circuit diagram

    Pressure

    p

    Time t

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    © Festo Didactic GmbH & Co. TP 601, 26Transparency

    Pressure switches

    2

    31

    1

    2 3

    Pressurep

    Time t

    4 bar

    pp

    27

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    4/3-way solenoid valve

    Valve spool is directly actuated by solenoids.

    The piston spool is displaced to the right and creates the connections P – A

    and B – T.

    Rest position produced by spring centring of piston spool. All inputs of the 4/3-way

    valve are closed in this position.

    T A P B

    T A P B

    A

    a b

    B

    P T

    a

    a

    b

    b

    Actuation on left

    Rest position

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    © Festo Didactic GmbH & Co. TP 601, 27Transparency

    4/3-way solenoid valve

    A

    a b

    B

    P T

    T A P B

    T A P B

    28

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    4/3-way solenoid valve, piloted

    Direct activation of pilot spool via solenoids.

    The pilot piston spool is displaced to the right, and hydraulic fluid is directed to the

    right-hand side of the main control spool, creating the connections P – A and B – T.

    Rest position produced by spring centring of pilot and main piston spools. All ports

    of the 4/3-way valve are closed at the main valve.

    Simplified symbol

    P T

    A

    A

    B

    B

    P T

    PB AT

    Detailed symbol

    Actuation on left

    Rest position

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    P T

    © Festo Didactic GmbH & Co. TP 601, 28Transparency

    4/3-way solenoid valve, piloted

    A

    A

    B

    B

    P T

    PB AT

    29

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    Electrical safety 

      EMERGENCY STOP button placed in an easily accessible position

      Protection against voltages

      Protection by means of insulation

     

    Protection by means of earthed conductive housings  Safety isolation by means of transformers

    L1

    24 V

    PE

    N

    1) Switch off 2) Check

    3) Carry out workEMERGENCY 

    STOP

    Basic insulation

    Additionalinsulation

    220 V AC

    Safety insulation Protective earth Safety isolation

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    © Festo Didactic GmbH & Co. TP 601, 29Transparency

    Electrical safety

    Safety insulation Protective earth Safety isolation

    30

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    Hydraulic safety 

    Safety regulations must be observed.

      Switch off motor/pump

      Depressurise accumulator

      Lower load

      Check pressure

    Work can now be carried out by authorised trained personnel.

    m

    1) Switch offmotor/pump

    2) Depressurise  accumulator

    4) Check  pressure

    3) Lower  load

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    © Festo Didactic GmbH & Co. TP 601, 30Transparency

    Hydraulic safety

    m