Chapter6 Basic Circuit

8/13/2019 Chapter6 Basic Circuit

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Basic Pneumatic Circuitry

For control and automation

Chapter 6

WUHAN UNIVERSITY OF TECHNOLOGY LOGISTICS ENG. DEPT.


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Contents

Symbols

Circuit layout Actuator control 2/2 Valve

Actuator control 3/2 Valve

Actuator control 5/2 Valve

Sequence solution

5/3 Valves Poppet/spool logic

Balanced spool logic

Feedback

Sequential control

Click the section to advance directly to it

Introduction

Chapter 6


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Introduction This module shows the

methods of application ofpneumatic valves andcomponents for control and

automation The methods of pure

pneumatic sequential controlare confined to simpleexamples

The majority of modernsystems are controlledelectronically and is thesubject of electro-pneumaticmodules

A message to pneumatic

circuit designers:

Use proven and reliable

design techniques

Produce circuits anddocumentation that are

clear to read

Design for safety

Do not try to be too

clever, the circuit will be

difficult for others to read

and maintain

Chapter 6


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Symbols The standard for fluid power symbols is ISO 1219-1. This

is a set of basic shapes and rules for the construction offluid power symbols

Cylinders can be drawn to show their extreme or

intermediate positions of stroke and any length abovetheir width

Valves show all states in the one symbol. The prevailingstate is shown with the port connections

Other components are single state symbols

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Symbols single acting actuators

Single acting, sprung

instroked


outstroked


instroked, magnetic

Single acting, sprungoutstroked, magnetic

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Symbols double acting actuators

Double acting, non-cushioned

Double acting, adjustablecushions

Double acting, throughrod, adjustable cushions

Double acting, magnetic,adjustable cushions

Double acting, rodless,magnetic, adjustable

cushions

Chapter 6


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Symbols rotary actuators

Semi-rotary double

acting

Rotary motor single

direction of rotation

Rotary motor bi-

directional

Chapter 6


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Symbols valves

2/2 Valve push button

/ spring


/spring

3/2 Valve detented

lever operated

2

13

12 10

21012

1

1

2

312

10

Chapter 6


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Symbols valves 3/2 Valve differential

pressure operated


/ spring

5/3 Valve double

pressure operated

spring centre

1

24

5 3

14 12

1

24

5 3

1

2

3

12 10

Chapter 6


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Symbols valves A valve function is known by a pair of numbers e.g. 3/2.

This indicates the valve has 3 main ports and 2 states

The valve symbol shows both of the states

Port numbering is to CETOP RP68P and shows:

when the valve is operated at the 12 end port 1 is connected toport 2

when reset to the normal state at the 10 end port 1 is connectedto nothing (0)

2

13

12 10

Chapter 6


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Symbols valves

A valve function is known by a pair of numbers e.g. 3/2.This indicates the valve has 3 main ports and 2 states

The valve symbol shows both of the states

Port numbering is to CETOP RP68P and shows:

when the valve is operated at the 12 end port 1 is connected toport 2

when reset to the normal state at the 10 end port 1 is connectedto nothing (0)

2

13

12 10

Chapter 6


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Symbols valves This example is for a 5/2

valve

This has 5 main ports and 2states

When the valve is operatedat the 14 end port 1 isconnected to port 4 (also

port 2 is connected to port 3)

When reset to the normalstate at the 12 end port 1 isconnected to port 2 (also

port 4 is connected to port 5)

1

24

5 3

14 12

Chapter 6


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Symbols valves

This example is for a 5/2 valve

This has 5 main ports and 2states

When the valve is operated at

the 14 end port 1 is connectedto port 4 (also port 2 isconnected to port 3)

When reset to the normal state

at the 12 end port 1 is connectedto port 2 (also port 4 isconnected to port 5)

1

24

5 3

14 12

Chapter 6


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Symbols operators manual

General manual

Push button

Pull button

Push/pull button

Lever

Pedal

Treadle

Rotary knob

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Symbols operators mechanical

Plunger

Spring normallyas a return

Roller

Uni-direction

or one way trip

Pressure

Pilot pressure

Differential pressure

Detent in 3 positions

Chapter 6


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Symbols 5/3 valves

All valves types shown in the normal position

Type 1. All ports blocked

Type 2. Outlets to exhaust

Type 3. Supply to outlets

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Symbols function components Non-return valve Flow regulator uni-

directional

Flow regulator bi-directional

Two pressure AND Shuttle valve OR

Silencer

Quick exhaust valve with

silencer

Pressure to electric switch

adjustable* Note: Traditional symbol in

extensive use (preferred)

*

ISO 1219-1 Old

Chapter 6


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Symbols air line equipment Water separator with

automatic drain

Filter with manual drain

Filter with automatic drain

Filter with automatic drainand service indicator

Lubricator

Pressure regulator with

gauge F.R.L. filter, regulator,

lubricator simplified symbol

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Circuit layout The standard for circuit

diagrams is ISO 1219-2

A4 format or A3 folded toA4 height for inclusion ina manual with other A4documentation

To be on several sheets ifnecessary with lineidentification code

Minimum crossing lines Limit valves position of

operation by actuatorsshown by a marker withreference code to symbol

Circuits should be drawnwith all actuators at the

top of the page in order of

sequential operation

Other components to be

drawn in sequential orderfrom the bottom up and

from left to right

Circuit should show the

system with pressure

applied and ready to start

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Component identification The ISO suggested

component numberingsystem is suited for largecircuits and those drawn onseveral pages

For this presentation asimple code is used

For cylinders: A,B,C etc.

For associated feedback

valves: alpha-numeric codea0for proof of instroke,a1for proof of outstroke

For cylinder B: b0 and b1

A

a0 a1

1

2

3

12 10

a0

2

13

12 10

a1

Note: the a0 valvesymbol is drawn in theoperated position becausethe actuator A isinstroked

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Example circuit

Run/End

A

a0 a1

B

b0 b1

C

c0 c1

a0 a1 b0b1 c0c1

10 bar max 6 barTo all inlet ports marked

Sequence

Run/End

A+

B+B-

C+

C-

A-

Repeat

Chapter 6


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Actuator control 2/2 valve

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2/2 Valve actuator control A pair of the most basic of

all valve types the 2/2 canbe used to control a singleacting cylinder

The normally closed

position of the valve isproduced by the spring

The operated position isproduced by the push

button One valve admits air the

other valve exhausts it

21012

1

11012

2OUT IN

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2/2 Valve actuator control The button marked OUT is

pushed to operate thevalve

Air is connected to thecylinder and it outstrokes

Air cannot escape toatmosphere through thevalve marked IN as this isclosed

The air at atmosphericpressure in the front of thecylinder vents through the

breather port

210

1

1211012

2OUT IN

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2/2 Valve actuator control The push button of the

valve marked OUT isreleased and it returns to anormal closed position

Air is now trapped in thesystem and provided thereare no leaks the piston rodwill stay in the outstroked

position

If the load increasesbeyond the force exertedby the air the piston rodwill start to move in

210

1

1211012

2OUT IN

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2/2 Valve actuator control The button marked IN is

pushed to operate the valve

Air escapes and the pistonrod moves to the instroked

position

The push button must beheld operated until the

piston rod is fully in

Atmospheric air will be

drawn in to the front of thecylinder through the vent

port

210

1

121

2

1012

OUT IN

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2/2 Valve actuator control To control the speed of

the piston rod, flowrestrictors are placed inthe pipes close to each ofthe valves.

Adjustment of therestrictors will slow downthe flow rate therebygiving independent

outstroke and instrokespeed control

1012 1012

OUT IN

2

1

1

2

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2/2 Valve actuator control By repeated operation

of either buttonduring movement the

piston rod can be

moved in small stepsfor approximate

positioning

This will only be

successful under slowspeeds

1012 1012

OUT IN

2

1

1

2

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2/2 Valve actuator control With any compressed air

system that intentionallytraps air, the potentialhazard of this must berecognised

Unintended release orapplication of pressure cangive rise to unexpectedmovement of the piston rod

A pressure indicator orgauge must be fitted towarn of the presence of

pressure

210

1

121

2

1012

OUT IN

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3/2 valve actuator control A 3 port valve provides the inlet

and exhaust path and is thenormal choice for the control ofa single acting cylinder

In the normal position producedby the spring, the valve is closed

In the operated positionproduced by the push button thevalve is open

The push button must be helddown for as long as the cylinderis outstroked

1

2

3

12 10

Chapter 6


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and exhaust path and is thenormal choice for the control of asingle acting cylinder


In the operated position producedby the push button the valve isopen

The push button must be helddown for as long as the cylinder isoutstroked

1

2

3

12 10

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and exhaust path and is thenormal choice for the control ofa single acting cylinder


In the operated positionproduced by the push button thevalve is open

The push button must be helddown for as long as the cylinderis outstroked

1

2

3

12 10

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3/2 valve actuator control To generally slow the

cylinder speed an adjustable

bi-directional flow regulator

or fixed restrictor can be

used The flow regulator setting

will be a compromise as the

ideal outstroke speed may

not produce the desiredresults for the instroke speed

1

2

3

12 10

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3/2 valve actuator control To control the outstroke speed

of a single acting cylinderwithout controlling theinstroke speed, a uni-directional flow regulator is

used

The flow into the cylindercloses the non return valve andcan only pass through the

adjustable restrictor By adjusting the restrictor the

outstroke speed of the cylindercan be set

1

2

3

12 10

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3/2 valve actuator control

For independent speed

control in each direction two

flow regulators are required

Installed in oppositedirections to each other

Upper regulator controls the

outstroke speed

Lower regulator controls theinstroking speed

1

2

3

12 10

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3/2 valve actuator control A 3 port valve provides the

inlet and exhaust path and is thenormal choice for the control ofa single acting cylinder

In the normal position produced

by the spring, the valve isclosed

In the operated positionproduced by the push button the

valve is open The push button must be held

down for as long as the cylinderis outstroked

1

2

3

12 10

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Chapter 6


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5/2 Valve actuator control For a double acting cylinder the

power and exhaust paths areswitched simultaneously

When the button is pushed thesupply at port 1 is connected to

port 4 and the outlet port 2connected to exhaust port 3. Thecylinder moves plus

When the button is released port 1

is connected to port 2 and port 4connected to port 5. Cylinderminus

1

24

5 3

14 12

+-

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5/2 Valve actuator control Independent speed control

of the plus and minusmovements

In most applications speed

is controlled by restrictingair out of a cylinder

Full power is developed todrive the piston with speed

controlled by restrictingthe back pressure

1

24

5 3

14 12

+-

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5/2 Valve actuator control Independent speed control of

the plus and minus movements

In most applications speed is

controlled by restricting air out

of a cylinder Full power is developed to

drive the piston with speed

controlled by restricting the

back pressure

1

24

5 3

14 12

+-

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5/2 Valve actuator control

Valves with a spring return aremono-stable and need theoperator to be held all the timethat the cylinder is required inthe plus position

Bi-stable valves will stay in theposition they were last set

The lever valve exampleillustrated indicates a detentmechanism. The lever need not

be held once the new positionhas been established

1

24

5 3

14 12

+-

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Manual control

Remote manual control of adouble acting cylinder

Valve marked + will causethe cylinder to outstroke ormove plus

Valve marked - will causethe cylinder to instroke ormove minus

The 5/2 double pilot valveis bi-stable therefore the

push button valves onlyneed to be pulsed

1

24

5 3

14 12

1

2

3

12 10

1

2

3

12 10

+ -

+-

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Manual control




The 5/2 double pilot valve

is bi-stable therefore thepush button valves onlyneed to be pulsed

1

24

5 3

1

2

3

12 10

1

2

3

12 10

14 12

+ -

+-

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Manual control Remote manual control of

a double acting cylinder





1

24

5 3

1

2

3

12 10

1

2

3

12 10

14 12

+ -

+-

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Manual control






1

24

5 3

14 12

1

2

3

12 10

1

2

3

12 10

+ -

+-

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Manual control Remote manual control of

a double acting cylinder





1

24

5 3

14 12

1

2

3

12 10

1

2

3

12 10

+ -

+-

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Semi-automatic control Manual remote start

of a double actingcylinder withautomatic return

Cylinder identified asA

Trip valve operated atthe completion of the

plus stroke identifiedas a1

1

24

5 3

14 12

1

2

3

12 10

1

2

3

12 10

+ -

+-

A

a1

a1

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Fully-automatic control Continuous automatic

cycling from rolleroperated trip valves

Manual Run and End ofthe automatic cycling

Cylinder will come to restin the instroked positionregardless of when thevalve is put to End

Tags for the rollerfeedback valves a0 anda1 show their relative

positions

1

24

5 3

14 12

2

13

12 10

1

2

3

12 10

1

2

312

10

Run/End

+-

A

a0 a1

a0 a1

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Sequential control

Chapter 6


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Circuit building blocks

These circuits can be considered as building blocks forlarger sequential circuits consisting of two or more

cylinders Each actuator will have a power valve and two associated

feedback valves. The first actuator to move also hasa Run/End valve

Run/End

A B

a0 a1 b0 b1

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Repeat pattern sequence

A repeat pattern sequenceis one where the order ofthe movements in the firsthalf of the sequence isrepeated in the secondhalf

Each actuator may haveone Out and In strokeonly in the sequence

There may be anynumber of actuators inthe sequence

The signal starting thefirst movement must passthrough the Run/Endvalve

Needs only the basicbuilding blocks to solve

Examples of repeatpattern sequences:

A+ B+ C+ D+ A- B- C-

D- A- B+ C- A+ B- C+

C+ A+ B- C- A- B+

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The two cylinders A and B are to perform a simple repeat

pattern sequence as follows: A+ B+ A- B- Apply the rule The signal given by the completion of

each movement will initiate the next movement

In this way the roller valves can be identified and labelled

Run/End

A B

a0a1b0 b1

a0 a1 b0 b1

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For three cylinders A, B and C also to perform a simple

repeat pattern sequence as follows: A+ B+ C+ A- B- C- Apply the rule The signal given by the completion of

each movement will initiate the next movement

Run/End

A

c0 c1

a0 a1

B

a0a1

b0 b1

C

b0b1

c0 c1

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Non-repeat pattern sequence

If the rule applied to a repeat pattern sequence is applied

to any other sequence there will be opposed signals onone or more of the 5/2 valves preventing operation

This circuit demonstrates the problem

The sequence is A+ B+ B- A-

Run/End

A B

b1a1a0 b0

a0 a1 b0 b1

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Opposed signals

When the valve is set to Run, cylinder A will not move

because the 5/2 valve has an opposed signal, it is stillbeing signalled to hold position by the feedback valve b0

If A was able to move + a similar problem will occur forthe 5/2 valve of B once it was +

The sequence is A+ B+ B- A-

Run/End

A B

b1a1a0 b0

a0 a1 b0 b1

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Mechanical solution

The problem was caused by valves b0 and a1 being

operated at the time the new opposing instruction is given If these two valves were one way triptypes and over

tripped at the last movement of stroke, only a pulse wouldbe obtained instead of a continuous signal

Run/End

A B

b1a1a0

a0 a1 b0 b1

b0

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Sequence solution methods

The main solutions tosolving sequences are:

Cascade (pneumatic)

Shift register (pneumatic)

Electro-pneumatic

PLC (Programmablelogic controller)

Cascade circuits providea standard method ofsolving any sequence. It

uses a minimum ofadditional logic hardware(one logic valve pergroup of sequential steps)

Shift register circuits aresimilar to cascade but useone logic valve for everystep

Electro-pneumatic

circuits use solenoidvalves and electro-mechanical relays

PLC. The standardsolution for medium tocomplex sequentialsystems (except whereelectrical equipmentcannot be used)

Chapter 6

Ch 6


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Cascade two group The A+ B+ B- A- circuit

is solved by the twogroup cascade method

The sequence is dividedat the point where B

immediately returns The two parts are

allocated groups l and ll

Gp l A+ B+ / Gp ll B- A-

Two signal supplies areprovided from a 5/2 valveone is available only ingroup l the other isavailable only in group ll

Because only one groupoutput is available at a

time it is not possible to

have opposed signals

A standard 5/2 doublepressure operated valve

is the cascade valve

1

24

5 3

14 12

Group l Group ll

Select l Select ll

Chapter 6

Ch t 6


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Cascade (two group)A B

a1

b0

a0 a1 b0 b1

Run/End

a0 b1

Sequence

Gp l A+ B+ Gp ll B- A-

Gp l

Gp ll

Chapter 6

Ch t 6


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a1

b0

a0 a1 b0 b1

Run/End

a0 b1

Sequence


Gp l

Gp ll

Chapter 6

Ch t 6


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b0

a0 a1 b0 b1

Run/End

a1

a0 b1

Sequence


Gp l

Gp ll

Chapter 6

Ch t 6


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b0

a0 a1 b0 b1

Run/End

a1

a0 b1

Sequence


Gp l

Gp ll

Chapter 6

Chapter 6


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a0 a1 b0 b1

Run/End

a1

a0

Sequence


Gp l

Gp ll

b0

b1

Chapter 6

Chapter 6


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a0 a1 b0 b1

Run/End

Sequence


Gp l

Gp ll

b0

b1

a1

a0

Chapter 6

Chapter 6


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Cascade building blocks

A two group buildingblock consists of a levervalve to run and end thesequence plus the 5/2double pilot operated

cascade valve For a two group system

consisting of any numberof cylinders this building

block and the cylinder

building blocks are allthat is required to solvethe sequence

1

24

5 3

14 12

1

2

312

10

Gp l

Gp ll

Sel l

Sel llRun/End

Chapter 6

Chapter 6


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Cascade building blocksGp l

Gp ll

Sel lSel ll

Gp lll

Sel lll

Run/End

This three groupbuilding block

establishes an

interconnecting

pattern that can

be extended to

any number of

groups

Chapter 6

Chapter 6


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Dual trip building blocks When a sequence has a

cylinder operating twice inone overall sequence a dualtrip building block may berequired for each of the two

feedback valves The supply will be from

different groups and theoutput go to differentdestinations

Example is for feedbackvalve a1 of cylinder A whenA is sent + both in Group xand Group y

Send A+

A+ in

Group xA+ in

Group y

a1

a1 in x

a1 in y

Note: can often be rationalised to less

than these three components

Chapter 6

Chapter 6


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Cascade rules

Establish the correctsequence

Divide the sequence in togroups. Always start asequence with the Run/End

valve selecting group l e.g.R/E | A+ B+ | B- C+ | C- A-

Select the cylinder buildingblocks

Select the cascade buildingblock

Select dual trip buildingblocks if required

Interconnect the blocks as follows: The first function in each group is

signalled directly by that groupsupply

The last trip valve operated ineach group is supplied with main

supply air and selects the nextgroup

The remaining trip valves aresupplied with air from theirrespective groups and initiate thenext function

Therun/end

valve will controlthe signal from the last trip valve

to be operated

Chapter 6

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Three position valves

Chapter 6

Chapter 6


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5/3 Valve

5/3 valves have a thirdmid position

The valve can be tri-stable e.g. a detentedlever operator or mono-

stable e.g. a double air ordouble solenoid withspring centre

There are three commonconfigurations for the mid

position: All ports blocked

Centre open exhaust

Centre open pressure

The majority ofapplications are

actuator positioning

and safety

24

15 314 12

14 1224

15 3

14 1224

15 3

Chapter 6

Chapter 6


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The valve illustrated has allports blockedin the midposition

Whenever the mid position isselected the pressure

conditions in the cylinder willbe frozen

This can be used to stop thepiston at part stroke in somepositioning applications

Flow regulators mounted closeto the cylinder to minimisecreep

24

15 314 12

Chapter 6

Chapter 6


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The valve illustrated hasallports blockedin the mid

position

Whenever the mid position isselected the pressure conditions

in the cylinder will be frozen This can be used to stop the

piston at part stroke in somepositioning applications

Flow regulators mounted close tothe cylinder to minimise creep

24

15 314 12

Chapter 6

Chapter 6


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The valve illustrated hasallports blockedin the mid

position




Flow regulators mountedclose to the cylinder tominimise creep

24

15 314 12

Chapter 6

Chapter 6


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The valve illustrated hasall ports blockedin themid position

Whenever the mid positionis selected the pressure

conditions in the cylinderwill be frozen

This can be used to stop thepiston at part stroke insome positioningapplications


24

15 314 12

p

Chapter 6


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5/3 Valve actuator control The valve illustrated has all

ports blockedin the midposition





24

15 314 12

p

Chapter 6


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This version of a 5/3 valve iscentre open exhaust

The supply at port 1 isisolated and the cylinder has

power exhausted when this

centre position is selected The version illustrated shows

a mono-stable version doublepilot operated spring centre

The cylinder will be pre-exhausted when changingfrom the mid position

24

15 3

14 12

p

Chapter 6


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This version of a 5/3 valve iscentre open pressure

The supply at port 1 isconnected to both sides of thecylinder and the exhaust ports

isolated when this centreposition is selected

Can be used to balancepressures in positioningapplications

The version illustrated ismono-stable, double solenoid,spring centre

1

24

5 3

14 12

p

Chapter 6


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Logic functions for poppet and

spool valves

p

Chapter 6


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Logic AND

To obtain the output Z both

plungers X AND Y must be

operated and held

If X only is operated the air will

be blocked at port 1 in valve Y

If Y only is operated there will be

no pressure available at port 1

If either X or Y is released the

output signal Z will be lost

1

2

3

12 10

1

2

3

12 10

X

Y

Z

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Logic AND To obtain the output Z both


operated and held


be blocked at port 1 in valve Y If Y only is operated there will

be no pressure available at port 1

If either X or Y is released the

output signal Z will be lost

1

2

3

12 10

1

2

3X

Y

Z

12 10

Chapter 6


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operated and held



be no pressure available at port

1

If either X or Y is released theoutput signal Z will be lost

1

2

3

12 10

1

2

3

12 10

X

Y

Z

Chapter 6


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operated and held




1


1

2

3

1

2

3

12 10

X

Y

Z

12 10

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operated and held




1


1

2

3

1

2

3X

Y

Z

12 10

12 10

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plungers X AND Y must beoperated and held

If X only is operated the airwill be blocked at port 1 in

valve Y

If Y only is operated there willbe no pressure available at port1


1

2

3

1

2

3

12 10

X

Y

Z

12 10

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Logic AND

To obtain the output Z bothplungers X AND Y must beoperated and held

If X only is operated the airwill be blocked at port 1 in

valve Y

If Y only is operated there willbe no pressure available atport 1


1

2

3

12 10

1

2

3

12 10

X

Y

Z

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Logic AND

This method must notbe usedas a two handed safety control

It is too easy to abuse. e.g. one

of the buttons could be

permanently fixed down andthe system operated from the

other button only

Use the purpose designed two

handed safety control unit

1

2

3

12 10

1

2

3

12 10

X

Y

Z

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Logic OR

Use of an ORfunctionshuttle valve

Source X and Y can beremote from each other andremote from the destination

of Z When X or Y is operated the

shuttle valve seal movesacross to prevent the signal Zfrom being lost through theexhaust of the other valve

X

Y

Z

1

2

3

12 10

1

2

3

12 10

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Logic OR




shuttle valve seal movesacross to prevent the signalZ from being lost throughthe exhaust of the othervalve

X

Y

Z

1

2

3

12 10

1

2

3

12 10

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Logic OR

Use of anOR

functionshuttle valve



shuttle valve seal movesacross to prevent the signalZ from being lost through

the exhaust of the othervalve

X

Y

Z

1

2

3

12 10

1

2

3

12 10

Chapter 6


93/134

Logic OR

Use of anOR

functionshuttle valve



shuttle valve seal movesacross to prevent the signalZ from being lost through

the exhaust of the othervalve

X

Y

Z

1

2

3

12 10

1

2

3

12 10

Chapter 6


94/134

Logic OR




shuttle valve seal movesacross to prevent the signal Z

from being lost through theexhaust of the other valve

X

Y

Z

1

2

3

12 10

1

2

3

12 10

Chapter 6


95/134

Logic NOT A logic NOT applies to the state

of the output when the operatingsignal is present (the output issimply an inversion of theoperating signal)

The valve shown is a normallyopen type (inlet port numbered 1)

When the signal X is presentthere is NOT output Z

When X is removed output Z isgiven

2

31

12 10

Z

X

Chapter 6


96/134

Logic NOT

A logic NOT applies to the stateof the output when the operatingsignal is present (the output issimply an inversion of theoperating signal)

The valve shown is a normallyopen type (inlet port numbered 1)



2

31

12 10

Z

X

Chapter 6


97/134

Logic NOT

A logic NOT applies to the stateof the output when the operatingsignal is present (the output issimply an inversion of theoperating signal)

The valve shown is a normallyopen type (inlet port numbered1)



2

31

12 10

Z

X

Chapter 6


98/134

Logic MEMORY

A logic MEMORY allowsthe output signal state (ON orOFF) to be maintained afterthe input signal has beenremoved

Any bi-stable valve is a logicMEMORY

With this lever detented valve,once the lever has been

moved X direction or Ydirection it can be releasedand will stay in that position

Z

X

1310

Y

12

Chapter 6


99/134

Logic MEMORY

A logic MEMORY

allows the output

signal state (ON orOFF) to be

maintained after the

signal that set it has

been removed

Z

X13

12 10 Y

Chapter 6


100/134

Logic MEMORY

A bi-stable double

pilot valve can be set

or reset simply by apulse (push and

release) on buttons X

or Y

Z

13

X

Y1

2

3

12 10

1

2

3

12 10

12 10

Chapter 6


101/134

Logic MEMORY

A bi-stable double




or Y

Z

13

X

Y1

2

3

12 10

1

2

3

12 10

12 10

Chapter 6


102/134

Logic MEMORY

A bi-stable double




or Y

Z

13

X

Y1

2

3

12 10

1

2

3

12 10

12 10

Chapter 6


103/134

Logic MEMORY

A bi-stable double




or Y

Z

13

X

Y1

2

3

12 10

1

2

3

12 10

12 10

L i MEMORY

Chapter 6


104/134

Logic MEMORY

A bi-stable double


or reset simply by a

pulse (push and


or Y

Z

13

X

Y1

2

3

12 10

1

2

3

12 10

12 10

L i MEMORY (l h)

Chapter 6


105/134

Logic MEMORY (latch)

A popular memory circuit isthe latch

Will not re-make afterpneumatic power failure

A pulse on X operates the pilot

/ spring valve to give output Z A feedback from Z runs

through the normally openvalve Y to latch the operationof Z when X is released

A pulse on Y breaks the latchand Z is exhausted

X

Y

Z

13

1

2

3

12 10

1012

3

2

1

12 10

i O (l h)

Chapter 6


106/134




A pulse on X operates the

pilot / spring valve to giveoutput Z

A feedback from Z runsthrough the normally openvalve Y to latch the operationof Z when X is released


X

Y

Z

13

1

2

3

12 10

12 10

3

2

1

12 10

L i MEMORY (l t h)

Chapter 6


107/134




A pulse on X operates the pilot/ spring valve to give output Z

A feedback from Z runsthrough the normally openvalve Y to latch the operation

of Z when X is released A pulse on Y breaks the latch

and Z is exhausted

X

Y

Z

13

1

2

3

12 10

12 10

3

2

1

12 10

Chapter 6


108/134


A popular memory circuit is thelatch


A pulse on X operates the pilot/ spring valve to give output Z

A feedback from Z runsthrough the normally openvalve Y to latch the operation

of Z when X is released A pulse on Y breaks the latch

and Z is exhausted

X

Y

Z

13

1

2

3

12 10

3

2

1

12 10

12 10

L i MEMORY (l t h)

Chapter 6


109/134




A pulse on X operates thepilot / spring valve to giveoutput Z

A feedback from Z runsthrough the normally open

valve Y to latch the operationof Z when X is released


X

Y

Z

13

1

2

3

12 10

3

2

1

12 10

12 10

Chapter 6


110/134

Logic arrangements for fully

balanced spool valves

L i i it ( l l )

Chapter 6


111/134

Logic circuits (spool valves)

Selection / Diversion

Latch

OR, AND, NOT Single pulse maker

Slow pressure build

Pre-select

Single pulse control

Air conservation

Double flow Counting

5/2 OR

Click the section to advance directly to it

NO / NC

3/2 NO / NC

Chapter 6


112/134

3/2 NO / NC

A fully balanced valveallows pressure on any potor combination of ports

A single valve can be usednormally open or normally

closed For normally open the

supply pressure is connectedto port 1

For normally closed thesupply pressure is connectedto port 3

1

2

3

12 10

2

13

12 10

/ /

Chapter 6


113/134

3/2 NO / NC

A fully balanced valve allowspressure on any pot orcombination of ports

A single valve can be usednormally open or normally

closed For normally open the supply

pressure is connected to port1

For normally closed thesupply pressure is connectedto port 3

1

2

3

12 10

2

13

12 10

3/2 V l l ti / di i

Chapter 6


114/134

3/2 Valve selection / diversion

Selection of one of twosupplies connected to

ports 1 and 3 can be

different pressures

Diversion of one supplyto one of two outlets

If it is required to exhaust

the downstream air a 5/2

valve is required

1

2

3

12 10

2

13

12 10


Chapter 6


115/134


Selection of one of twosupplies connected to

ports 1 and 3 can be

different pressures

Diversion of one supplyto one of two outlets

If it is required to exhaust

the downstream air a 5/2

valve is required

1

2

3

2

13

12 10

12 10

L t h ith t l

Chapter 6


116/134

Latch with controls

In this version of a latchthe push button valves areconnected to perform ORand NOTfunctions

The OFFvalve must be

placed last in the signalchain so that if bothvalves are operatedtogether the OFFcommand will dominate

over the ONcommand

1

2

3

12 10

2

13

12 10

2

13

12 10

ON

OFF

Out

OR AND NOT

Chapter 6


117/134

OR, AND, NOT

A single 3/2 pilotoperated spring return

valve can be use for any

of these logic functions

xOR ygives output z

xAND ygives output z

xgives NOT z

1

2

3

12 10

1

2

3

12 10

1

2

3

12 10

AND

OR

NOT

x y

z

x y

z

x

z

Si le l e ke

Chapter 6


118/134

Single pulse maker Converts a prolonged

signal xinto a single

pulse z

Signal z must be removed

to allow the valve to reset

then x can be appliedagain

The duration of the pulse

can be adjusted with the

flow regulator

1

2

3

12 10

x

z

Slow initial pressure build up

Chapter 6


119/134

Slow initial pressure build up Choose a 3/2 pilot spring

valve with a relatively highoperating force e.g. 3 to 4

bar

When the quick connectcoupling is made, the outputat port 2 is controlled at therate of the flow regulatorsetting

When the pressure is high

enough to operate the valvefull flow will take over

1

2

3

12 10

Pre select

Chapter 6


120/134

Pre-select The lever valve can pre-

select the movement ofthe cylinder OUT or IN

The movement will occurthe next time the plunger

valve is operated The plunger valve can be

released immediately andsubsequently operatedand released any number

of times

1

2

3

12 10

1

2

3

12 10

1

2

3

12

10

OUT/INpre-select

5/2 OR function

Chapter 6


121/134

5/2 OR function

The valve at position aisreversed connected and

supplied from the valve

conventionally connected

at position b

The cylinder can be

controlled from either

position aORposition

b

1

24

5 3

1412

1

24

5 3

1412

a

b


Chapter 6


122/134


24

1412

1

2

3

12 10

15

12 10

1

2

3

2

13

1210

Each time the foot

operated valve ispressed the cylinderwill single stroke +and - alternately

First foot operationthe cylinder movesout

Second foot operationthe cylinder moves in

Third.. out and soon

Air conservation

Chapter 6


123/134

Air conservation Power stroke in the instroke

direction only Differential area of the piston

gives an outstroke force whenthe pressure is balanced

Air used to outstroke isequivalent to a cylinder withonly the same bore as the roddiameter

Assumes the cylinder is not

loaded on the plus stroke andlow friction

24

15

14 12

Air conservation

Chapter 6


124/134

Air conservation Power stroke in the instroke

direction only Differential area of the

piston gives an outstrokeforce when the pressure is

balanced

Air used to outstroke isequivalent to a cylinderwith only the same bore asthe rod diameter

Assumes the cylinder is notloaded on the plus strokeand low friction

24

15

14 12

Double flow

Chapter 6


125/134

Double flow Where a larger 3/2 valve

is not available Two flow paths in a 5/2

valve each with aseparate supply can bearranged to give doubleflow or supply separatedevices

Ensure the tube size tothe cylinder is large

enough to take the doubleflow

4 2

1 3

1214

5 1

Double flow

Chapter 6


126/134

Double flow Where a larger 3/2 valve

is not available Two flow paths in a 5/2

valve each with aseparate supply can bearranged to give doubleflow or supply separatedevices

Ensure the tube size tothe cylinder is large

enough to take the doubleflow

4 2

1 3

1214

5

Counting

Chapter 6


127/134

Counting Counting applications are best

achieved with electro-mechanical or programmableelectronic counters

Pneumatic counting circuits use

large numbers of logic valvesand can be slow

The counting chain shown willcount to 4

Red and blue are non-overlapping alternate pulses,

purple is the reset line

1

2

3

4

Counting application

Chapter 6


128/134

Counting application

The counting circuit is appliedto count 4 strokes of a cylinder

At rest all counting valves areheld reset by the start valve

Start outstrokes A

Alternate signals from a1anda0progresses operation of thecounting valves up the chain

On the 4th operation of a1the

green signal resets the startvalve to stop the cylinder

A

a0a1

a0 a1

Start

Chapter 6


129/134

Feedback methods

Time delay

Chapter 6


130/134

Time delay A signal is restricted to

slow the rate of pressurebuild up on a pressureswitch (3/2 differential

pressure operated valve)

When the pressure switchoperates a strong un-restricted output is given

A reservoir providescapacitance to allow less

fine and sensitive settingson the flow regulatormaking it easy to adjust

1

2

3

12 10

Signal

in

Output

Time delay

Chapter 6


131/134

Time delay Manual remote start

of a double acting

cylinder with a time

delay in the

outstroked positionbefore automatic

return

2

1

24

5 3

14 12

13

12 10

+-

A

a1

1

2

3

12 10

a1

1

2

3

12 10

Pressure decay

Chapter 6


132/134

Pressure decay Manual remote start of a

double acting cylinder Uses a low pressure

operated valve connectednormally open

When the back pressure in

the front of the cylinderfalls below 0.1 bar thereturn signal is given

Connection taken between

the cylinder and flowregulator

Useful for pressing workpieces of variable size

1

24

5 3

14 12

2

13

12 10

+-

A

a1

21210

1 3 0.1bar

Electro-pneumatic

Chapter 6


133/134

Electro pneumatic The majority of systems use

electrical/electronic controldue to the high degree ofsophistication and flexibility

Solenoid valves are used tocontrol cylinders

Feedback signals are fromreed switches, sensors andelectrical limit switches

Logic is hard wired or

programmed in to a PLC(programmable logiccontroller)

a0 a1

1

24

5 3

14 12

A

a0 a1

Circuit building block for

each cylinder

Chapter 6


134/134

End

Documents

Chapter6 Basic Circuit