1. Pneumatics

2. 2/2 Way Directional Control Valve (Flow Switch)
Control Valve Symbols
For every control valve status a square is drawn
The ports are indicated (on the initial status) :-
Output Port ( Top )
Inlet Port ( Bottom )
2/2 Way Directional Control Valve (Flow Switch)
Flow is indicated by an arrow ( No flow by lines at right angles )

3. Actuation of Control Valves :-1. Mechanical
General
Pushbutton
Lever Operated
Foot Pedal
Spring Return
Spring Centered
Roller
Idle Return Roller

4. Actuation of Control Valves :-2. Electrical / Pneumatic
Direct Pneumatic
Indirect Pneumatic
Pressure Release
Single Solenoid
Double Solenoid
Electro-Pneumatic

5. Describe this Control Valve ?
The control valve has two positions
The control valve has four ports
The control valve is operated by a Pushbutton and returned by a Spring
4/2 Way Directional Pushbutton Control Valve with Spring Return
The control valve changes the flow direction at the output ports

6. Linear Actuators Single Acting Cylinder Double Acting Cylinder
Double Acting Cylinder with double ended piston
Double Acting Cylinders with non-adjustable and adjustable cushioning on one or both ends

7. 3/2 Pneumatic Control Valve
Actuate
Spring Return
Actuate
Spring Return 2

8. 3/2 Pneumatic Control Valve driving a Linear Actuator
Open 2
Non-Actuated
Actuated
Open 2
What Happens if the Pressure Supply is lost ?

9. 5/2 Pneumatic Control Valve
Actuate
Spring Return
Actuate
Spring Return

10. 5/2 Pneumatic Control Valve driving a Linear Actuator
Non-Actuated
Open
Actuated
Open
What Happens if the Pressure Supply is lost ?

11. Cascade Valves for higher flows 2
How does this improve cylinder flow rates ?

12. Flow Control Elements - 1
Check Valve
Spring Loaded Check Valve
Quick Exhaust Valve
Adjustable Flow Control
One-Way Flow Control

13. Improved Speed of Actuator Return2
How does this improve cylinder performance ?

14. Actuator Flow Rate Control
What is restricted by each flow valve ?

15. Flow Control Elements - 2
Shuttle Valve (Or Gate ) A Z B
A B Z A Z B
Two Pressure Valve (AND Gate)
A B Z

16. Logical Switching Operation
What Happens if the Pressure Supply is lost ?

17. Flow Control Elements - 3
Time Delay Valve
Sequence Valve

18. Timing Actuator Operation

19. Pneumatic Switches to indicate Actuator Position
Roller Limit Switch
How does this change the circuit operation ?

20. Design Exercise
Extend the previous circuit so that the actuator holds for the time delays in continuous cyclic operation
Change the above circuit so that it cycles continuously without delay

21. Design Exercise SolutionsA+ A-
Circuit Diagram
To Remove delays simply remove delay units ?

22. Sequential Operation From the previous Circuit note :
If the sequence is to commence on a start signal a manual start valve is needed
An Actuator needs an individual pneumatically driven control valve
Each identified sequence position needs a switch driven valve
Connections between valves programme the desired sequence, i.e. A- A+ a- a+
A+ Actuator direct.
a+ Valve
Where :-

23. Two Actuator Operation
For the following sequence
then we require :
a start valve, and
two cylinders driven by pneumatically operated 5/2 control valves, and
four switch driven 3/2 directional valves A+ B+ a+ b+ A- a- B- b-
Start

24. Solution : A+ a+ a- A- B+ B- b- b+
Start

25. Actuator ‘Trapping’ Consider the following sequence :
All is well until we try to retract actuator B via b+ as it will still be actuated by a+ and hence remain in the initial activated position.
A conflict for actuator A occurs for b- and a-
This ‘trapping’ always occurs when a sequence calls for a reversing of an actuator without any intervening motion of another actuator. A+ B+ a+ b+ B- b- A- a-
Start

26. Solution : Isolate Pressure Sourcesb- A- B+ B- a- b+
Start

27. Electro-Pneumatics Advantages Electrical transmission time quicker
Programming Flexibility
Greater Sensor availability
Disadvantages
small actuation forces
physically large and power consuming for large force applications

28. How do solenoid actuators work ?
An electrical conductor creates a magnetic field around it whose density ( B ) is proportional to the size of the current ( I ) passing through it
The greater the number of conductor turns ( N ) the stronger the magnetic field
A former ( mr ) is used to align and concentrate the resulting magnetic field
Ampere’s Law :

29. Electrical Symbols 1 :- Switches
Normally Open
Normally Closed
Mechanically Linked
General manual
Press activated
Pull activated
Rotate activated
Roller activated

30. Electrical Symbols 2 :- Indicators and Instruments
Horn
Lamp
Audio
LED
General Instrument
Ammeter
Voltmeter A V

31. Electrical Circuit Diagrams
Signal Flow
+24V A 0V
Energy Supplies
Input Elements
Processing and Final Control Elements

32. Logical Switching Circuits
NOT Gate
AND Gate
OR Gate
A B Z
A Z A B

33. Problem Exercises
Design and build an electric circuit that will activate a single acting linear actuator and an indicator light whenever a switch is operated.
Repeat the above but using a double acting linear actuator and a spring return valve
Repeat 2 above but use a double solenoid activated valve

34. Solutions : Y1
Exercise 1
Exercise 2 ?
Exercise 3 Y1
Start
+24V 0V

35. Design Exercise 1
Comment upon possible problems with the following circuits :
Circuit 1
Circuit 2
Start
+24V 0V Y1 Y2 Y1
Start
+24V 0V

36. Design Exercise 2
For failsafe operation spring return valves/actuators are often used.
Design an electro-pneumatic circuit to extend an actuator on application of a manual set switch and hold it extended via an electrical limit switch. Retracting the actuator only on application of a reset switch.

37. Exercise 2 Solution - Part 1Y1
OUT
Set
+24V 0V
Reset
Open when retracted
What Happens if the Set switch is released prior to the actuator becoming fully extended ?

38. Exercise 2 Solution - Part 2
To overcome this problem then move the limit switch to the retract position and use the normally closed contacts, i.e :
Set
+24V 0V
Reset IN Y1
Open when retracted

39. Relays
Electromagnetic devices which use a solenoid to control a number of contacts mechanically. They offer the following advantages :-
Switch large current systems ( via contacts ) from small currents ( to coil )
Switch multiple contacts
Provide ‘Memory’

40. Electrical Symbols 3 :- Relays
Electro-mechanical
Delay energised
Delay de-energised
Single active winding
AC relay
Thermal relay
Indicating DC resistance
Driving a Shut-off valve
500

41. How may we overcome the memory of the electro-pneumatic valve seen in exercise 3 previously ?K1
Start
+24V 0V Y1 Y2 Y2 Y1

42. Relay Latching for ‘Memory’K1
Start
+24V 0V
Reset
Set Dominant
Reset Dominant

43. ‘Failsafe’ Latching Design Exercise
For failsafe operation spring return valves/actuators are often used.
Using a relay design an electro-pneumatic circuit to extend and hold extended an actuator on application of a manual set switch, and retract the actuator on application of a reset switch.

44. ‘Failsafe’ Latching SolutionY1 K1
Set
+24V 0V
Reset