Lisnagarvey High School
Technology and Design GCSE
Pneumatic Systems Content (Unit 2)
(From 2009)
A. Pneumatic Principles
2.
pages 2-3
Calculating Force Outputs
- Working out the pressure
- Working out the area
- Calculating the force
3.
Sample pneumatic force questions
B. Pneumatic Symbols
4.
C.
page 4
Pneumatic Symbols
Pneumatic Circuits
pages 5-12
5
Circuit 1
Single Acting Cylinder operated using a Push button operated/spring return
3/2 valve.
5
Circuit 2
AND Circuit - Single acting cylinder operated using two push button
operated/spring return 3/2 valves.
6
Circuit 3
OR Circuit - Single acting cylinder operated using two push button
operated/spring return 3/2 valves and shuttle valve
7
Circuit 4
Double Acting Cylinder using two 3/2 valves to provide pilot signals to a
Pilot Operated/Pilot Return 5/2 valve.
8
Circuit 5
Double Acting Cylinder using two 3/2 valves to provide pilot signals to a
Pilot Operated/Pilot Return 5/2 valve with speed control on the outstroke.
9
Circuit 6
Automatic reciprocation of a double acting cylinder using two carefully
positioned 3/2 valves (A and B) with speed control on the outstroke.
10
Circuit 7
Double Acting Cylinder using two 3/2 valves to provide pilot signals to a
Pilot Operated/Pilot Return 5/2 valve. A time delay on the outstroke is
provided by a reservoir and uni-directional flow control valve (one-way
flow restrictor.)
11-12 Circuit 8
Automatic reciprocation of two Double Acting Cylinders using four 3/2
valves (two plunger and two roller) to provide pilot signals to two Pilot
Operated/Pilot Return 5/2 valves. Speed control on outstroke and instroke
of both cylinders provided by four one-way restrictor valves.
Name:_________________________________
Pneumatic Principles
Calculating force output
There is only one formula you need in pneumatics - that for calculating the force output from a
cylinder. You will be given the formula sheet at the front of your GCSE answer book. So all you have
to do is make sure you know how to use it!
The force you get out of a cylinder depends on the air pressure inside it, and the size or area of the
piston. The formula is:
F
Force (F) = Pressure (p) × Area (a)
P
A
A. Working out the pressure
In the formula, pressure must be given in Newtons/mm² (N/mm²). So if pressure is shown in bar you
must convert it to N/mm². To convert bars to N/mm² simply divide by 10. i.e 1 Bar = 0.1N/ mm²
For example: 5 bar = 5 ÷ 10 = 0.5N/mm²
B. Working out the area
The area is the surface area of the piston. As every piston is round, you may have to calculate
the area of the circular piston from the radius. To do this, use the formula for area of a circle:
Area (A) = π × r² (r is the radius of the piston in mm)
(taking π to be 3.14).
or
Area (A) = π x d²/4 (d is the diameter of the piston in mm)
For example: if a piston has a radius of 30mm, the surface area of the piston is:
A = 3.14 × 30²
=
3.14 × 30 × 30
=
2826mm²
C. Calculating the force
The force you get from a piston is measured in Newtons (N). Here's a sample problem:
A piston has a radius of 20mm and the pressure in the cylinder is 4 bar. Calculate the force output.
1. Convert the units of pressure: Pressure = 4bar = 0.4N/mm²
(Remember divide by 10)
ii. Next, work out the area: Area = 3.14 × 20 × 20 = 1256mm²
(Remember A= π × r²)
iii. Finally you can calculate the force output from the cylinder:
Force = 0.4 × 1256 = 502.4N
(Remember F = P x A)
Sample Pneumatic Force Questions
Pressure
Cylinder Size
Force
0.5N/mm²
A=1256mm²
F=? (N)
1256 x 0.5 = 628N
2 Bar
R=20mm
F=? (N)
2/10 = 0.2N/mm2
A = 3.14 x 20 x 20
1256 x 0.2 = 251N
1256mm2
1Bar
D=50mm
F=? (N)
1 / 10 = 0.1 N/mm2
3.14 x 25 x 25
1962.5 x 0.1=
=1962.5 mm2
196 N
R=? (mm)
1000N
2 Bar
2 / 10 =0.2 N/mm2
A = F/P
1000/0.2 = 5000mm2
R = 40mm
P=? (N/mm²)
D=40mm
P= F/A
3.14 x 20 x 20
2000/1256 = 1.6N/mm2
= 1256mm2
2000N
Main Components
General Symbols
Methods of Valve
Activation
Circuit 1 Single acting cylinder operated using a Push button
operated/spring return 3/2 valve
1.
When the push-button on the 3/2 valve is pressed, it moves to the right causing air to go through
the valve. Air goes through the valve causing the single acting cylinder to outstroke.
2.
When the push button is released the spring causes the valve to move back to the left to its
original position and the single acting cylinder instrokes. The spring in the cylinder forces it
back as the air behind the cylinder goes out through the exhaust of the valve.
Circuit 2 AND Circuit - Single acting cylinder operated using two
push button operated/spring return 3/2 valves
B
A
1. When the push-button on the 3/2 valve A is pressed, it moves to the right causing air to go through to
the 3/2 valve B. The air can go no further and stops at valve B. Only when the push button on valve B
is pressed and valve B moves to the right can air goes through valve B causing the single acting
cylinder to outstroke.
2. When the push button of either valve is released the spring in that valve causes the valve to move
back to the left to its original position and the single acting cylinder instrokes. The spring in the
cylinder forces it back as the air in the cylinder goes out the exhaust of whichever valve is released.
This is called an AND circuit as both valves A and B need to be pressed and held to cause the cylinder
to outstroke. The order that the valves are pressed is not important. If either valve is released the
cylinder will instroke.
This is a safety circuit – used so that you cannot accidently outstroke a circuit by hitting a button – both
need to be pressed. Any number of valves can be added in sequence.
Circuit 3 OR Circuit - Single acting cylinder operated using two push
button operated/spring return 3/2 valves and shuttle valve
SV
A
B
1. When the push-button on the 3/2 valve A is pressed, it moves to the right causing air to go
through to the shuttle valve SV. The air pushes the little ball in the shuttle valve over to the
right and the air continues on to the single acting cylinder causing it to outstroke.
2. When the push button is released the cylinder will instroke as normal.
3. The same process will happen if the push button on the 3/2 valve B is pressed. The air will go to
the shuttle valve SV and push the ball to the left and the air continues on to the single acting
cylinder causing it to outstroke.
4. Again, when the push button is released the cylinder will instroke.
5. If both 3/2 valves are pressed at the same time, the cylinder will again outstroke.
This is called an OR circuit as to make the cylinder outstroke you need to push valve A OR valve B
OR both. You can continue to add 3/2 valves, but for each additional one, you will need an
additional shuttle valve. This circuit is mainly used for convenience, as it allows you to operate a
cylinder from a number of valves.
Circuit 4
Double Acting Cylinder using two 3/2 valves to provide pilot signals to
a Pilot Operated/Pilot Return 5/2 valve
A
B
In the circuit there are two push button 3/2 valves, which are used to operate the 5/2 valve. The 5/2
switches by air pressure going in one side or the other. This is called pilot operation. The dashed lines
indicate pilot operation and there needs to be a certain air pressure to switch the valve.
1.
When the push-button on the 3/2 valve A is pressed, it moves to the right causing air to go
through the valve and into the left hand side of the 5/2 valve. The 5/2 valve operates (moves to the
right) causing the cylinder to outstroke.
2.
When the push button is pressed on the second 3/2 valve B, the 5/2 valve will switch back (to
the left), triggering the release of air and causing the cylinder to instroke.
* Remember that a 5/2 valve is a memory valve i.e it will stay in a position until it is made to
move by pushing one or other of the push button valves *
Questions:
1. Which valve makes the cylinder outsroke? _____________
2. Which valve makes the cylinder instroke? ______________
3. Why does the 5/2 valve have no buttons to operate it?
________________________________________________________________________________
______________________________________________
Circuit 5
Double Acting Cylinder using two 3/2 valves to provide pilot signals to
a Pilot Operated/Pilot Return 5/2 valve with speed control on the
outstroke.
A
B
This circuit is very similar to circuit 1 and its general operation is the same except that it includes speed
control of the cylinder on its outstroke, as explained below.
1. When the push-button on the 3/2 valve A is pressed, it moves to the right causing air to go through
the valve and into the left hand side of the 5/2 valve. The 5/2 valve operates (moves to the right)
causing the cylinder to outstroke.
2. Air in front of the piston rod is pushed out the cylinder. This exhaust air can be used to control the
speed of the outstroke by the unidirectional-flow control valve which is positioned the correct way
round. The speed of the outstroke can be changed by using the adjusting the knob on the valve.
3. When the push button is pressed on the second 3/2 valve B, the 5/2 valve will switch back (to the
left), triggering the release of air and causing the cylinder to instroke at its full speed. There is no
speed control on the instroke in this circuit.
Question – How can you provide speed control on the instroke of the cylinder?
________________________________________________________
Circuit 6
Automatic reciprocation of a double acting cylinder using two carefully
positioned 3/2 valves (A and B) with speed control on the outstroke.
B
A
This circuit is almost the same as circuit 2. The difference is simply that the 3/2 push button valves in
circuit 2 have been replaced by two other 3/2 valves (one is a roller activated and the other is a
plunger). These two valves are positioned carefully to make an automatic reciprocating circuit as
explained below.
1.
2.
3.
4.
5.
When the piston on the double-acting cylinder is retracted (completes the instroke), the piston
activates the roller on the 3/2 roller valve A, allowing air to pass through it.
The air output from valve A activates the left side of the 5/2 pilot valve (these are connected by
the dashed line), releasing air at the top left of the 5/2 and causing the piston to outstroke. Air in
front of the piston rod is pushed out the rod. This exhaust air can be used to control the speed of the
outstroke by the unidirectional-flow control valve.
When the piston is fully extended, it operates the plunger on the 3/2 plunger valve B to send out
an air signal.
The air released by the 3/2 valve B activates the right side of the 5/2 pilot valve (these are
connected by the dashed line). This signal causes air to be released from the top right of the 5/2
causing the piston to retract, or go negative.
When the piston on the double acting cylinder is retracted (completes the instroke), the piston
operates the roller-trip control and the cycle is then repeated.
Remember:
Double-acting cylinders are controlled by five-port valves. To slow a cylinder a unidirectional-flow
control valve is placed to slow the exhaust air, NOT the air going in.
Circuit 7
Double Acting Cylinder using two 3/2 valves to provide pilot signals to
a Pilot Operated/Pilot Return 5/2 valve. A time delay on the outstroke
is provided by a reservoir and uni-directional flow control valve (oneway flow restrictor.)
A
B
This circuit is very similar to circuit 1 and its general operation is the same except that it includes a
time delay for the cylinder to outstroke. The time delay is created by the addition of a one-way control
valve (unidirectional-flow control valve) and reservoir, as explained below.
1. When the push-button on the 3/2 valve A is pressed, the air flow is restricted by the unidirectionalflow control valve and it slowly enters the reservoir.
2. The pressure builds in the reservoir slowly, causing the time delay.
3. Only when the pressure in the reservoir is high enough will it operate the 5/2 valve, (pushing it over
to the right) triggering the release of air and causing the cylinder to outstroke.
4. When the push button is pressed on the second 3/2 valve B, the 5/2 valve will switch back (to the
left), triggering the release of air and causing the cylinder to instroke.
Exam tip:
Do not confuse time delay with speed control. Time delay (in circuit 4) prevents the piston operating
for a particular time period. Speed control (in circuit 2) reduces the speed of the piston's instroke or
outstroke, depending on where the unidirectional-flow control valve is positioned.
Questions – 1. How can the time delay be changed?
__________________________________________________________________________________ .
2. How could a time delay be put into the instroke of the cylinder?
____________________________________________________________________________
Circuit 8
Automatic reciprocation of two Double Acting Cylinders using four 3/2 valves (two plunger and two roller) to
provide pilot signals to two Pilot Operated/Pilot Return 5/2 valves. Speed control on outstroke and instroke
of both cylinders provided by four one-way restrictor valves.
3/2 PV B
CYL A
FRV1
FRV4
FRV2
FRV3
3/2 RV A
3/2 RV B
5/2 Valve A
3/2 PV A
CYL B
5/2 Valve B
1. CYL A retracts (instrokes) at a speed which is determined by the one-way
restrictor valve _______ and the ball hits the ___________________ This
valve activates and sends a pilot signal to the ______________ side of the
_____________________ .
2. This valve moves over to the left which allows air to enter the _______ of
CYL B, through the one-way restrictor valve FRV4. CYL B retracts
(instrokes) at a speed which is determined by the one-way restrictor valve
______ and the ball hits the ___________________. This valve activates
and sends a pilot signal to the _______________ side of the __________.
3. This valve moves over to the right which allows air to enter the ______ of
CYL A, through the one-way restrictor valve FRV1. CYL A extends
(outstrokes) at a speed which is determined by the one-way restrictor valve
______ and the ball hits the _____________________This valve activates
and sends a pilot signal to the _____________ side of the _____________.
4. This valve moves over to the right which allows air to enter the ______ of
CYL B, through the one-way restrictor valve FRV3. CYL B extends
(outstrokes) at a speed which is determined by the one-way restrictor valve
______ and the ball hits the _____________________This valve activates
and sends a pilot signal to the _____________ side of the ____________.
5. This valve moves over to the left which allows air to enter the _______ of
CYL A, through the one-way restrictor valve FRV2. CYL A retracts
(instrokes) at a speed which is determined by the one-way restrictor valve
___________ and the ball hits the _____________ which starts the
complete cycle all over again (from point 1).
The cycle will continue over and over again until there is a cut in air supply
somewhere in the circuit or any of the valves lose their position. This is a
fully automatic circuit.
To enable the system to be stopped in a desired position a 3/2 lever valve(s)
can be put into a pilot line(s), depending on how you want the cylinder
positions to stop.
Remember the order that cycle for this circuit is
CYL A instrokes (-), CYL B instrokes (-), CYL A outstrokes (+), CYL B
outstrokes (+), CYL A instrokes (-) etc.