Pneumatic circuits.pptx

Basic Pneumatic Circuitry
For control and automation

Contents
 Symbols
 Circuit layout
 Actuator control 2/2 Valve
 Sequence solution
 5/3 Valves
 Poppet/spool logic
 Balanced spool logic
 Feedback
 Sequential control
Click the section to advance directly to it
 Introduction

Introduction
 This module shows the
methods of application of
pneumatic valves and
components for control
and automation
 The methods of pure
pneumatic sequential
control are confined to
simple examples
 The majority of modern
systems are controlled
electronically and is the
subject of electro-
pneumatic modules
 A message to pneumatic
circuit designers:
 Use proven and reliable
design techniques
 Produce circuits and
documentation 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

Symbols
 The standard for fluid power symbols is ISO 1219-1. This is
a set of basic shapes and rules for the construction of
fluid power symbols
 Cylinders can be drawn to show their extreme or
intermediate positions of stroke and any length above
their width
 Valves show all states in the one symbol. The prevailing
state is shown with the port connections
 Other components are single state symbols

Symbols single acting actuators
 Single acting, sprung
instroked
outstroked
instroked, magnetic
outstroked, magnetic

Symbols double acting actuators
 Double acting, non-
cushioned
 Double acting, adjustable
cushions
 Double acting, through
rod, adjustable cushions
 Double acting, magnetic,
adjustable cushions
 Double acting, rodless,
magnetic, adjustable
cushions

Symbols rotary actuators
 Semi-rotary double acting
 Rotary motor single
direction of rotation
 Rotary motor bi-
directional

Symbols valves
 2/2 Valve push button /
spring
spring
 3/2 Valve detented lever
operated
2
1
3
12 10
2
10
12
1
1
2
3
12
10

Symbols valves
 3/2 Valve differential
pressure operated
spring
 5/3 Valve double pressure
operated spring centre
1
2
4
5 3
14 12
1
2
4
5 3
1
2
3
12 10

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
to port 2
 when reset to the normal state at the 10 end port 1 is
connected to nothing (0)
2
1
3
12 10

Symbols valves
 This example is for a 5/2
valve
 This has 5 main ports and
2 states
 When the valve is
operated at the 14 end
port 1 is connected to
port 4 (also port 2 is
connected to port 3)
 When reset to the normal
state at the 12 end port 1
is connected to port 2
(also port 4 is connected
to port 5)
1
2
4
5 3
14 12

Symbols operators manual
General manual
Push button
Pull button
Push/pull button
Lever
Pedal
Treadle
Rotary knob

Symbols operators mechanical
Plunger
Spring normally
as a return
Roller
Uni-direction
or one way trip
Pressure
Pilot pressure
Differential pressure
Detent in 3 positions

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

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

Symbols air line equipment
 Water separator with
automatic drain
 Filter with manual drain
 Filter with automatic drain
 Filter with automatic drain
and service indicator
 Lubricator
 Pressure regulator with
gauge
 F.R.L. filter, regulator,
lubricator simplified
symbol

Circuit layout
 The standard for circuit
diagrams is ISO 1219-2
 A4 format or A3 folded to
A4 height for inclusion in
a manual with other A4
documentation
 To be on several sheets if
necessary with line
identification code
 Minimum crossing lines
 Limit valves position of
operation by actuators
shown by a marker with
reference code to symbol
 Circuits should be drawn
with all actuators at the
top of the page in order of
sequential operation
 Other components to be
drawn in sequential order
from the bottom up and
from left to right
 Circuit should show the
system with pressure
applied and ready to start

Component identification
 The ISO suggested
component numbering
system is suited for large
circuits and those drawn
on several pages
 For this presentation a
simple code is used
 For cylinders: A,B,C etc.
 For associated feedback
valves: alpha-numeric
code ‘a0’ for proof of
instroke, ‘a1’ for proof of
outstroke
 For cylinder B: b0 and b1
A
a0 a1
1
2
3
12 10
a0
2
1
3
12 10
a1
 Note: the a0 valve symbol
is drawn in the operated
position because the
actuator A is instroked

Example circuit
Run/End
A
a0 a1
B
b0 b1
C
c0 c1
a0 a1 b0
b1 c0
c1
10 bar max 6 bar
To all inlet ports marked
Sequence
Run/End
A+
B+
B-
C+
C-
A-
Repeat

2/2 Valve actuator control
 A pair of the most basic
of all valve types the 2/2
can be used to control a
single acting cylinder
 The normally closed
position of the valve is
produced by the spring
 The operated position is
produced by the push
button
 One valve admits air the
other valve exhausts it
2
10
12
1
1
10
12
2
OUT IN

 The button marked OUT
is pushed to operate the
valve
 Air is connected to the
cylinder and it outstrokes
 Air cannot escape to
atmosphere through the
valve marked IN as this is
closed
 The air at atmospheric
pressure in the front of
the cylinder vents
through the breather port
2
10
1
12
1
10
12
2
OUT IN

 The push button of the
valve marked OUT is
released and it returns to
a normal closed position
 Air is now trapped in the
system and provided
there are no leaks the
piston rod will stay in the
outstroked position
 If the load increases
beyond the force exerted
by the air the piston rod
will start to move in
2
10
1
12
1
10
12
2
OUT IN

 The button marked IN is
pushed to operate the
valve
 Air escapes and the
piston rod moves to the
instroked position
 The push button must be
held operated until the
piston rod is fully in
 Atmospheric air will be
drawn in to the front of
the cylinder through the
vent port
2
10
1
12
1
2
10
12
OUT IN

 If the button marked IN is
released the piston rod
will remain in the
instroked position
 Any leaks in the
installation can cause the
piston rod to creep
2
10
1
12
1
2
10
12
OUT IN

 To control the speed of
the piston rod, flow
restrictors are placed in
the pipes close to each of
the valves.
 Adjustment of the
restrictors will slow down
the flow rate thereby
giving independent
outstroke and instroke
speed control
10
12 10
12
OUT IN
2
1
1
2

 By repeated operation of
either button during
movement the piston rod
can be moved in small
steps for approximate
positioning
 This will only be
successful under slow
speeds
10
12 10
12
OUT IN
2
1
1
2

 With any compressed air
system that intentionally
traps air, the potential
hazard of this must be
recognised
 Unintended release or
application of pressure
can give rise to
unexpected movement of
the piston rod
 A pressure indicator or
gauge must be fitted to
warn of the presence of
pressure
2
10
1
12
1
2
10
12
OUT IN

3/2 valve actuator control
 A 3 port valve provides
the inlet and exhaust path
and is the normal choice
for the control of a single
acting cylinder
 In the normal position
produced by the spring,
the valve is closed
 In the operated position
produced by the push
button the valve is open
 The push button must be
held down for as long as
the cylinder is outstroked
1
2
3
12 10

 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 desired
results for the instroke
speed
1
2
3
12 10

 To control the outstroke
speed of a single acting
cylinder without
controlling the instroke
speed, a uni-directional
flow regulator is used
 The flow into the cylinder
closes the non return
valve and can only pass
through the adjustable
restrictor
 By adjusting the restrictor
the outstroke speed of
the cylinder can be set
1
2
3
12 10

 For independent speed
control in each direction
two flow regulators are
required
 Installed in opposite
directions to each other
 Upper regulator controls
the outstroke speed
 Lower regulator controls
the instroking speed 1
2
3
12 10

 For a double acting
cylinder the power and
exhaust paths are
switched simultaneously
 When the button is
pushed the supply at port
1 is connected to port 4
and the outlet port 2
connected to exhaust
port 3. The cylinder
moves plus
 When the button is
released port 1 is
connected to port 2 and
port 4 connected to port
5. Cylinder minus
1
2
4
5 3
14 12
+
-

 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
2
4
5 3
14 12
+
-

 Valves with a spring
return are mono-stable
and need the operator to
be held all the time that
the cylinder is required in
the plus position
 Bi-stable valves will stay
in the position they were
last set
 The lever valve example
illustrated indicates a
detent mechanism. The
lever need not be held
once the new position
has been established
1
2
4
5 3
14 12
+
-

Manual control
 Remote manual control of
a double acting cylinder
 Valve marked + will cause
the cylinder to outstroke
or move plus
 Valve marked - will cause
the cylinder to instroke or
move minus
 The 5/2 double pilot valve
is bi-stable therefore the
push button valves only
need to be pulsed
1
2
4
5 3
14 12
1
2
3
12 10
1
2
3
12 10
+ -
+
-

Manual control
 Remote manual control of
a double acting cylinder
 Valve marked + will cause
the cylinder to outstroke
or move plus
 Valve marked - will cause
the cylinder to instroke or
move minus
 The 5/2 double pilot valve
is bi-stable therefore the
push button valves only
need to be pulsed
1
2
4
5 3
1
2
3
12 10
1
2
3
12 10
14 12
+ -
+
-

Semi-automatic control
 Manual remote start of a
double acting cylinder
with automatic return
 Cylinder identified as “A”
 Trip valve operated at the
completion of the plus
stroke identified as “a1”
1
2
4
5 3
14 12
1
2
3
12 10
1
2
3
12 10
+ -
+
-
A
a1
a1

Fully-automatic control
 Continuous automatic
cycling from roller
operated trip valves
 Manual Run and End of
the automatic cycling
 Cylinder will come to rest
in the instroked position
regardless of when the
valve is put to End
 Tags for the roller
feedback valves a0 and
a1 show their relative
positions
1
2
4
5 3
14 12
2
1
3
12 10
1
2
3
12 10
1
2
3
12
10
Run/End
+
-
A
a0 a1
a0 a1

Circuit building blocks
 These circuits can be considered as building blocks for
larger 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 has
a Run/End valve
Run/End
A B
a0 a1 b0 b1

Repeat pattern sequence
 A repeat pattern
sequence is one where
the order of the
movements in the first
half of the sequence is
repeated in the second
half
 Each actuator may have
one Out and In stroke
only in the sequence
 There may be any number
of actuators in the
sequence
 The signal starting the
first movement must pass
through the Run/End
valve
 Needs only the basic
building blocks to solve
 Examples of repeat
pattern sequences:
 A+ B+ C+ D+ A- B- C- D-
 A- B+ C- A+ B- C+
 C+ A+ B- C- A- B+

 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
a0
a1
b0 b1
a0 a1 b0 b1

 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
a0
a1
b0 b1
C
b0
b1
c0 c1

Non-repeat pattern sequence
 If the rule applied to a repeat pattern sequence is applied
to any other sequence there will be opposed signals on
one 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
b1
a1
a0 b0
a0 a1 b0 b1

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 still
being signalled to hold position by the feedback valve b0
 If A was able to move + a similar problem will occur for the
5/2 valve of B once it was +
 The sequence is A+ B+ B- A-
Run/End
A B
b1
a1
a0 b0
a0 a1 b0 b1

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 trip” types and over
tripped at the last movement of stroke, only a pulse would
be obtained instead of a continuous signal
Run/End
A B
b1
a1
a0
a0 a1 b0 b1
b0

Sequence solution methods
 The main solutions to
solving sequences are:
 Cascade (pneumatic)
 Shift register
(pneumatic)
 Electro-pneumatic
 PLC (Programmable
logic controller)
 Cascade circuits provide
a standard method of
solving any sequence. It
uses a minimum of
additional logic hardware
(one logic valve per group
of sequential steps)
 Shift register circuits are
similar to cascade but
use one logic valve for
every step
 Electro-pneumatic
circuits use solenoid
valves and electro-
mechanical relays
 PLC. The standard
solution for medium to
complex sequential
systems (except where
electrical equipment
cannot be used)

Cascade two group
 The A+ B+ B- A- circuit is
solved by the two group
cascade method
 The sequence is divided
at 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 are
provided from a 5/2 valve
one is available only in
group l the other is
available only in group ll
 Because only one group
output is available at a
time it is not possible to
have opposed signals
 A standard 5/2 double
pressure operated valve
is the cascade valve
1
2
4
5 3
14 12
Group l Group ll
Select l Select ll

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

Cascade (two group)
A B
b0
a0 a1 b0 b1
Run/End
a1
a0 b1
Sequence
Gp l
Gp ll

Cascade (two group)
A B
a0 a1 b0 b1
Run/End
a1
a0
Sequence
Gp l
Gp ll
b0
b1

Cascade (two group)
A B
a0 a1 b0 b1
Run/End
Sequence
Gp l
Gp ll
b0
b1
a1
a0

Cascade building blocks
 A two group building
block consists of a lever
valve to run and end the
sequence plus the 5/2
double pilot operated
cascade valve
 For a two group system
consisting of any number
of cylinders this building
block and the cylinder
building blocks are all
that is required to solve
the sequence
1
2
4
5 3
14 12
1
2
3
12
10
Gp l
Gp ll
Sel l
Sel ll
Run/End

Cascade building blocks
Gp l
Gp ll
Sel l
Sel ll
Gp lll
Sel lll
Run/End
 This three group
building block
establishes an
interconnecting
pattern that can
be extended to
any number of
groups

Dual trip building blocks
 When a sequence has a
cylinder operating twice
in one overall sequence a
dual trip building block
may be required for each
of the two feedback
valves
 The supply will be from
different groups and the
output go to different
destinations
 Example is for feedback
valve a1 of cylinder A
when A is sent + both in
Group x and Group y
Send A+
A+ in
Group x
A+ in
Group y
a1
a1 in x
a1 in y
Note: can often be rationalised to less
than these three components

Cascade rules
 Establish the correct
sequence
 Divide the sequence in to
groups. Always start a
sequence with the
Run/End valve selecting
group l e.g.
R/E | A+ B+ | B- C+ | C- A-
 Select the cylinder
building blocks
 Select the cascade
building block
 Select dual trip building
blocks if required
 Interconnect the blocks as
follows:
 The first function in each group
is signalled directly by that
group supply
 The last trip valve operated in
each group is supplied with
main supply air and selects the
next group
 The remaining trip valves are
supplied with air from their
respective groups and initiate
the next function
 The “run/end” valve will control
the signal from the last trip
valve to be operated

5/3 Valve
 5/3 valves have a third
mid position
 The valve can be tri-
stable e.g. a detented
lever operator or mono-
stable e.g. a double air or
double solenoid with
spring centre
 There are three common
configurations for the mid
position:
 All ports blocked
 Centre open exhaust
 Centre open pressure
 The majority of
applications are actuator
positioning and safety
2
4
1
5 3
14 12
14 12
2
4
1
5 3
14 12
2
4
1
5 3

 The valve illustrated has
“all ports blocked” in the
mid position
 Whenever the mid
position is selected the
pressure conditions in
the cylinder will be frozen
 This can be used to stop
the piston at part stroke
in some positioning
applications
 Flow regulators mounted
close to the cylinder to
minimise creep
2
4
1
5 3
14 12

 This version of a 5/3 valve
is “centre open exhaust”
 The supply at port 1 is
isolated and the cylinder
has power exhausted
when this centre position
is selected
 The version illustrated
shows a mono-stable
version double pilot
operated spring centre
 The cylinder will be pre-
exhausted when
changing from the mid
position
2
4
1
5 3
14 12

 This version of a 5/3 valve
is “centre open pressure”
 The supply at port 1 is
connected to both sides
of the cylinder and the
exhaust ports isolated
when this centre position
is selected
 Can be used to balance
pressures in positioning
applications
 The version illustrated is
mono-stable, double
solenoid, spring centre
1
2
4
5 3
14 12

Logic functions for poppet and
spool valves

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

Logic AND
held
1 in valve Y
will be no pressure
available at port 1
lost
1
2
3
12 10
1
2
3
X
Y
Z
12 10

Logic AND
held
1 in valve Y
will be no pressure
available at port 1
lost
1
2
3
1
2
3
12 10
X
Y
Z
12 10

Logic AND
held
1 in valve Y
will be no pressure
available at port 1
lost
1
2
3
1
2
3
X
Y
Z
12 10
12 10

Logic AND
 This method must not be
used as a two handed
safety control
 It is too easy to abuse.
e.g. one of the buttons
could be permanently
fixed down and the
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

Logic OR
 Use of an ‘OR’ function
shuttle valve
 Source X and Y can be
remote from each other
and remote from the
destination of Z
 When X or Y is operated
the shuttle valve seal
moves across to prevent
the signal Z from being
lost through the exhaust
of the other valve
X
Y
Z
1
2
3
12 10
1
2
3
12 10

Logic NOT
 A logic NOT applies to the
state of the output when
the operating signal is
present (the output is
simply an inversion of the
operating signal)
 The valve shown is a
normally open type (inlet
port numbered 1)
 When the signal X is
present there is NOT
output Z
 When X is removed
output Z is given
2
3
1
12 10
Z
X

Logic MEMORY
 A logic MEMORY allows
the output signal state
(ON or OFF) to be
maintained after the input
signal has been removed
 Any bi-stable valve is a
logic MEMORY
 With this lever detented
valve, once the lever has
been moved X direction
or Y direction it can be
released and will stay in
that position
Z
X
1
3
10
Y
12

Logic MEMORY
 A logic MEMORY allows
the output signal state
(ON or OFF) to be
maintained after the
signal that set it has been
removed
Z
X
1
3
12 10
Y

Logic MEMORY
 A bi-stable double pilot
valve can be set or reset
simply by a pulse (push
and release) on buttons X
or Y
Z
1
3
X
Y
1
2
3
12 10
1
2
3
12 10
12 10

Logic MEMORY (latch)
 A popular memory circuit
is the latch
 Will not re-make after
pneumatic power failure
 A pulse on X operates the
pilot / spring valve to give
output Z
 A feedback from Z runs
through the normally
open valve 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
1
3
1
2
3
12 10
10
12
3
2
1
12 10

is the latch
output Z
released
X
Y
Z
1
3
1
2
3
12 10
12 10
3
2
1
12 10

is the latch
output Z
released
X
Y
Z
1
3
1
2
3
12 10
3
2
1
12 10
12 10

Logic arrangements for fully
balanced spool valves

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
 A fully balanced valve
allows pressure on any
pot or combination of
ports
 A single valve can be
used normally open or
normally closed
 For normally open the
supply pressure is
connected to port 1
 For normally closed the
supply pressure is
connected to port 3
1
2
3
12 10
2
1
3
12 10

3/2 Valve selection / diversion
 Selection of one of two
supplies connected to
ports 1 and 3 can be
different pressures
 Diversion of one supply
to 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
1
3
12 10

3/2 Valve selection / diversion
 Selection of one of two
supplies connected to
ports 1 and 3 can be
different pressures
 Diversion of one supply
to one of two outlets
 If it is required to exhaust
the downstream air a 5/2
valve is required
1
2
3
2
1
3
12 10
12 10

Latch with controls
 In this version of a latch
the push button valves
are connected to perform
‘OR’ and ‘NOT’ functions
 The ‘OFF’ valve must be
placed last in the signal
chain so that if both
valves are operated
together the ‘OFF’
command will dominate
over the ‘ON’ command
1
2
3
12 10
2
1
3
12 10
2
1
3
12 10
ON
OFF
Out

OR, AND, NOT
 A single 3/2 pilot operated
spring return valve can be
use for any of these logic
functions
 x OR y gives output z
 x AND y gives output z
 x gives 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

Single pulse maker
 Converts a prolonged
signal x into a single
pulse z
 Signal z must be removed
to allow the valve to reset
then x can be applied
again
 The duration of the pulse
can be adjusted with the
flow regulator
1
2
3
12 10
x
z

Slow initial pressure build up
 Choose a 3/2 pilot spring
valve with a relatively
high operating force e.g.
3 to 4 bar
 When the quick connect
coupling is made, the
output at port 2 is
controlled at the rate of
the flow regulator setting
 When the pressure is
high enough to operate
the valve full flow will take
over
1
2
3
12 10

Pre-select
 The lever valve can pre-
select the movement of
the cylinder OUT or IN
 The movement will occur
the next time the plunger
valve is operated
 The plunger valve can be
released immediately and
subsequently operated
and released any number
of times
1
2
3
12 10
1
2
3
12 10
1
2
3
12
10
OUT/IN
pre-select

5/2 OR function
 The valve at position ‘a’ is
reversed connected and
supplied from the valve
conventionally connected
at position ‘b’
 The cylinder can be
controlled from either
position ‘a’ ‘OR’ position
‘b’
1
2
4
5 3
14
12
1
2
4
5 3
14
12
a
b

Single pulse control
2
4
14
12
1
2
3
12 10
1
5
12 10
1
2
3
2
1
3
12
10
 Each time the foot
operated valve is
pressed the cylinder
will single stroke +
and - alternately
 First foot operation
the cylinder moves
out
 Second foot
operation the
cylinder moves in
 Third….. out and so
on

Air conservation
 Power stroke in the
instroke direction only
 Differential area of the
piston gives an outstroke
force when the pressure
is balanced
 Air used to outstroke is
equivalent to a cylinder
with only the same bore
as the rod diameter
 Assumes the cylinder is
not loaded on the plus
stroke and low friction
2
4
1
5
14
12

Double flow
 Where a larger 3/2 valve
is not available
 Two flow paths in a 5/2
valve each with a
separate supply can be
arranged to give double
flow or supply separate
devices
 Ensure the tube size to
the cylinder is large
enough to take the double
flow
4 2
1 3
12
14
5 1

Double flow
 Where a larger 3/2 valve
is not available
 Two flow paths in a 5/2
valve each with a
separate supply can be
arranged to give double
flow or supply separate
devices
 Ensure the tube size to
the cylinder is large
enough to take the double
flow
4 2
1 3
12
14
5

Counting
 Counting applications are
best achieved with
electro-mechanical or
programmable electronic
counters
 Pneumatic counting
circuits use large
numbers of logic valves
and can be slow
 The counting chain
shown will count to 4
 Red and blue are non-
overlapping alternate
pulses, purple is the reset
line
1
2
3
4

Counting application
 The counting circuit is
applied to count 4 strokes
of a cylinder
 At rest all counting valves
are held reset by the start
valve
 Start outstrokes ‘A’
 Alternate signals from
‘a1’ and ‘a0’ progresses
operation of the counting
valves up the chain
 On the 4th operation of
‘a1’ the green signal
resets the start valve to
stop the cylinder
A
a0
a1
a0 a1
Start

Time delay
 A signal is restricted to
slow the rate of pressure
build up on a pressure
switch (3/2 differential
pressure operated valve)
 When the pressure switch
operates a strong un-
restricted output is given
 A reservoir provides
capacitance to allow less
fine and sensitive
settings on the flow
regulator making it easy
to adjust
1
2
3
12 10
Signal
in
Output

Time delay
with a time delay in the
outstroked position
before automatic return
2
1
2
4
5 3
14 12
1
3
12 10
+
-
A
a1
1
2
3
12 10
a1
1
2
3
12 10

Pressure decay
 Uses a low pressure
operated valve connected
normally open
 When the back pressure
in the front of the cylinder
falls below 0.1 bar the
return signal is given
 Connection taken
between the cylinder and
flow regulator
 Useful for pressing work
pieces of variable size
1
2
4
5 3
14 12
2
1
3
12 10
+
-
A
a1
2
12
10
1 3 0.1bar

Electro-pneumatic
 The majority of systems
use electrical/electronic
control due to the high
degree of sophistication
and flexibility
 Solenoid valves are used
to control cylinders
 Feedback signals are
from reed switches,
sensors and electrical
limit switches
 Logic is hard wired or
programmed in to a PLC
(programmable logic
controller)
a0 a1
1
2
4
5 3
14 12
A
a0 a1
 Circuit building block for
each cylinder

Pneumatic circuits.pptx

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