Circuits
[AIRLANE PNEUMATICS LTD]
Circuits
Basic Pneumatic Control Circuits
Pneumatic control systems range from the very simple manual push button control of, say, a simple
clamp to seemingly highly complex, fully automated control of, say, a pick and place machine.
All air circuit types obey the same basic principles and even the most complex circuits are little more
than several simple circuits interlinked to operate in a pre-determined sequence.
Understanding fully the desired sequence for your machinery is the key to unlocking the most
efficient and reliable control circuit for your application.
Fully pneumatic control systems have a number of benefits including: –
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Using only one utility – compressed air.
Easily configured and adjusted as processes evolve.
Parameter control is easily adjusted.
Involve AIRLANE from the CONCEPTION of your project and have full access to: –
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Over 40 years total experience and knowledge in pneumatic control.
Specialists in circuit design.
Product knowledge and specification.
Application knowledge and understanding.
Receive full and accurate parts lists.
Circuits designed are guaranteed to work to your agreed specification or we will re-design
and correct FREE OF CHARGE.
Receive full and accurate circuit diagrams upon completion of project.
Accurate invoicing – no hidden extras.
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Circuits
Simple Circuits
The simplest and most common air circuit consists of either a single-acting spring return or a doubleacting cylinder which is controlled by a 3 port 2 position (3/2) or 5 port 2 position (5/2) directional
valve, respectively.
The 3/2 directional valve is actuated causing the actuator to extend. Releasing the valve exhausts
the air and the internal spring reverses the cylinder to its home position.
The 5/2 directional valve is actuated by 3 port, 2 position (3/2) push button valves or electric
switches.
Auto-return and Reciprocating Cylinder Circuits
The easiest way to get a double acting cylinder to automatically return or reciprocate is by fitting trip
switches to the extremes of the cylinder’s stroke. When the trip switches are actuated by the
cylinder movement they pilot the main control valve and reverse the outputs causing the movement
of the cylinder to reverse.
In version 1 (below left) a trip switch is placed at the end of the cylinder travel. Pressing and
releasing the push button causes the cylinder to out stroke. When the trip switch is made it reverses
the 5/2 valve, causing the cylinder to return to its home position.
In version 2 (below right) the cylinder will continuously travel between the limit switches until one of
the signals is interrupted. The cylinder will start to reciprocate again as soon as the interruption is
removed.
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Circuits
Timing Circuits
In this circuit, the 3/2 valve is actuated and air is sent to the 5/2 valve. The 5/2 valve shifts, sending
air to the rear of the cylinder causing the cylinder to extend. Air also flows to the timer where it
begins to time to the pre-setting. Once reached, the timer opens, allowing the air to flow through to
the control valves other pilot port, shifting the valve back. Air flows through port 2, retracting the
cylinder.
In this circuit a constant air signal is sent to the timer. The normally open timer allows air to flow
through until the set time period expires. While air flows to the pilot of the control valve the cylinder
extends and remains extended. When the time period expires the cylinder returns even if the air
signal remains. Note: in this setup if the air signal is removed before the timer, the cylinder will
retract. The circuit will only recycle once the air signal is removed and reapplied.
Reciprocating Cylinder using Timers
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Circuits
This circuit can be used when a fixed time between cycles is preferred or when it is difficult to fit
limit switches to the cylinder. The circuit is similar to the reciprocating circuit shown above but the
trip switches are replaced with timers.
Three Position Function using 2 x 3/2 Valves or a 5/3 Valve
Use these set-ups to obtain a Three Position Function with either 2 x 3/2 N/O valves or a 5/3 valve.
Pressure Applied Set-Up (Centre Open to Pressure, COP)
This set-up is ideal for operating rodless cylinders where the piston area is equal on both sides. Both
valves are normally open, pressurising both sides of the cylinder.
Actuate the Left Valve to move piston to the left; actuate the Right Valve to move the piston to the
right. By releasing both valves the cylinder can be stopped at any position along its stroke.
Supply pressure must be equal on both left and right valves.
Pressure Relieved Set-Up (Centre Open to Exhaust, COE)
This set-up is recommended for use when both sides of the actuator must be fully exhausted during,
for example, an emergency stop procedure, to allow an entrapment to be removed.
Pressure Held Set-Up (All Ports Blocked, APB)
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Circuits
This set-up can be useful, but not ideal, for operating actuators that need to stop along their stroke
length and hold that position. Helps stop external forces from moving the actuator unexpectedly.
This is a crude method of control that is easily upset by leaking components and worn actuator or
valve seals. However, the easiest way to control a reversible air motor is to use a 5/3 All Closed Mid
Position Valve. The motor stops in the centre position and will rotate in the forward or reverse
direction selected using the 5/3 valve. Speed can be controlled by either adjusting the mains supply
pressure or by using flow regulators.
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Circuits
Two Hand ‘Anti Tie-Down’ Safety Extend and Single Hand Retract
Use this circuit when the operator is in danger from being trapped by the actuator. The circuit
utilises a Two Hand Safety Start ‘Anti Tie-Down’ valve to prevent the operator from trapping one
hand when operating machinery with the other hand. The danger lies during, for example, the
application of a force when clamping a part. This circuit will retract the cylinder if either hand
releases the Two Hand Start Valve. The cylinder will only hold the work piece in place once it has
reached its full stroke. Additionally with the use of the end of stroke sensor the circuit will work
even if clamping on material that is not consistently the same size.
Legend:
A
Two Hand Safety Start Valve
B
Shuttle Valve
C
5/2 Pilot Spring Valve
D
3/2 Normally Open Push Button
E
End of Stroke Sensor
Operation:
1. A Two Hand Safety Start Valve (A) is activated, sending a signal through the shuttle valve (B).
2. The signal pilots Valve C (5/2, Pilot/Spring), extending the cylinder. If A is released prior to
full extension of the cylinder, the cylinder will automatically retract.
3. When the cylinder reaches full extension, E (End of Stroke Sensor) sends a signal through D
(Normally Open Valve), through B (Shuttle Valve), holding pilot the pilot signal on A.
4. To retract the cylinder D is depressed, removing the pilot signal from C, allowing the spring
to reverse the 5/2 valve.
Two Hand Extend Two Hand Retract
Use this circuit, where a “pinch point” exists on both the
extension and retraction of the linear actuator. This circuit will
require the operator to use the two hand control for either
motion.
Legend:
A
Two Hand Safety Start Valve
B
5 Port, 2 Position Lever Operated Valve
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Circuits
C
5/3 Pilot Operated Valve, Spring to Centre, APB
Operation:
1. Operator sets B valve to either extend or retract cylinder.
2. Operator uses A (two hand control) to move cylinder.
3. If one or both buttons are not actuated cylinder will stop in place.
Two Hand Extend with Automatic Return
This circuit is useful for applications where cycle time and safety is an issue. With the Automatic
Return feature, the operator’s hands are tied down and the cylinder will return when the work is
completed, not when the operator removes their hands from the actuator.
Legend:
A
Two Hand Safety Start Unit
B
5 Port, 2 Position Pilot/Spring Valve
C
3/2 Double Pilot Operated Valve
D
5/2 Pilot/Spring Valve
E
3/2 Limit Switch
Operator uses Two Hand Start Unit to extend the cylinder, if one or both hands are removed,
cylinder returns. If limit is reached the cylinder will automatically return even if the operators’ hands
remain on the Two Hand Start Unit.
Emergency Stop and Reset Circuit
An emergency stop circuit must conform to ISO 13850 and achieve two parts to its control. Firstly,
operation of the emergency stop valve must bring the machine to a safe stop usually via a latching
emergency stop palm button valve. Secondly, upon releasing the latched e/stop the state of the
machine must not alter in any way, in particular, it must not restart! If the emergency stop has
dumped the air supply from the system (As in the example below) it must not be re-introduced until
the reset button is operated and this only after the machine is checked, made safe and the
emergency stop button is un-latched.
Tel: - 0191 5214140. sales@airlane.co.uk www.airlane.co.uk
Circuits
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Circuits
Cascade System Circuits
Circuit sequences that do not repeat the first half of the sequence in exactly the same order as the
second half experience problems with trapped signals and will not function as a simple circuit. A
solution to this problem is to use the CASCADE SYSTEM. This prevents trapped signals by turning on
and off mains air to trip valves as and when required. This is achieved by adding 5/2 double pilot
valves to give multiple groups of air.
The apparently simple sequences A+B+/B-A-, and, similarly, sequence A+B+C+/C-B-A- or any other
sequence where the first part of the sequence is not in exactly the same order as the second part
will need to use this cascade system.
An example of the simplest form of 2-Group Cascade and the reason for it is shown below.
The top diagram shows a standard A+B+/A-B- sequence. This works perfectly as there are no
trapped signals from the trip switches blocking the movement of either cylinder.
The middle diagram shows an A+B+/B-A- sequence. However, as you can see, the trip switches
connected to the valve controlling Cylinder A are BOTH live. This prevents the valve from changing
and, thus, the cylinder operating.
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Circuits
To overcome this issue we introduce the CASCADE Valve, an additional 5/2 Pilot/Pilot Valve that will
switch on and off the mains feeds to the trip switches, eliminating the trapped signals. The circuit in
the diagram below now works perfectly.
By adding cascade valves to your circuit: One additional valve gives a Two Group Cascade circuit
Two additional valves gives a 3 Group Cascade circuit
Three additional valves gives a 4 Group Cascade circuit
It is extremely rare to go above a 4 Group Cascade system.
Airlane have designed many complex circuits over the years. If you are in any doubt about how best
to design your controls please call and discuss it with us first.
Useful Accessories
Uni-Directional Flow Regulator.
An adjustable fitting used to restrict the flow of air passing through it one direction only, allowing
free flow in the opposite direction.
Used to control the speed of cylinders by
restricting the exhausting air
passing out of the cylinder port. We control the
exhaust air as it gives a smoother and
more controlled movement of the cylinder.
Shuttle Valve (OR-Gate).
A logic element that allows either of two separate signals to be used to pilot a control valve. (Either
signal A OR signal B) See examples in
the Emergency Stop and Reset Circuit or the Two
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Circuits
Hand ‘Ant i Tie-Down’ Safety Extend and Single Hand Retract circuit
Tel: - 0191 5214140. sales@airlane.co.uk www.airlane.co.uk