IL 0 Group II Group I Select GP I Select GP II Solution Basi

IL 0 Group II Group I Select GP I Select GP II

Solution

Basic Pneumatic Circuitry For control and automation 2. Contents Introduction Symbols Circuit layout Actuator control 2/2 Valve Actuator control 3/2 Valve Actuator control 5/2 Valve Sequential control Sequence solution 5/3 Valves Poppet/spool logic Balanced spool logic Feedback Click the section to advance directly to it 3. 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 electropneumatic 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 4. 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 5. Symbols single acting actuators Single acting, sprung instroked Single acting, sprung outstroked Single acting, sprung instroked, magnetic Single acting, sprung outstroked, magnetic 6. Symbols double acting actuators Double acting, noncushioned Double acting, adjustable cushions Double acting, through rod, adjustable cushions Double acting, magnetic, adjustable cushions Double acting, rodless, magnetic, adjustable cushions 7. Symbols rotary actuators Semi-rotary double acting Rotary motor single direction of rotation Rotary motor bidirectional 8. Symbols valves 2/2 Valve push button / spring 3/2 Valve detented lever operated 1 3/2 Valve push button / spring 2 10 12 2 10 12 3 2 10 12 3 1 1 9. Symbols valves 3/2 Valve differential pressure operated 2 12 3 10 1 5/2 Valve push button / spring 5/3 Valve double pressure operated spring centre 14 4 5 4 2 5 1 3 2 12 1 3 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 12 10 3 1 11. 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 12 10 3 1 12. 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) 4 2 14 12 5 1 3 13. 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) 4 2 14 12 5 1 3 14. Symbols operators manual General manual Lever Push button Pedal Pull button Treadle Push/pull button Rotary knob 15. Symbols operators mechanical Plunger Pressure Spring normally as a return Pilot pressure Roller Differential pressure Uni-direction or one way trip Detent in 3 positions 16. 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 17. Symbols function components Non-return valve Flow regulator unidirectional Flow regulator bidirectional 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 18. 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 19. 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 20. 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 Note: the a0 valve symbol is drawn in the operated position because the actuator A is instroked a0 a1 A 12 a0 3 2 1 10 2 10 12 a1 3 1 21. Example circuit a0 a1 b0 A b1 c0 B c1 C Sequence Run/End A+ B+ BC+ CARepeat Run/End a0 10 bar max b1 a1 6 bar To all inlet ports marked b0 c1 c0 22. Actuator control 2/2 valve 23. 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 12 OUT 2 10 1 12 IN 1 10 2 24. 2/2 Valve actuator control 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 12 OUT 2 1 10 12 IN 1 10 2 25. 2/2 Valve actuator control 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 12 OUT 2 10 1 12 IN 1 10 2 26. 2/2 Valve actuator control 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 12 OUT 2 10 1 12 IN 1 2 10 27. 2/2 Valve actuator control 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 12 OUT 2 10 1 12 IN 1 10 2 28. 2/2 Valve actuator control 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 2 10 12 OUT 1 1 10 12 IN 2 29. 2/2 Valve actuator control 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 2 10 12 OUT 1 1 10 12 IN 2 30. 2/2 Valve actuator control 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 12 OUT 1 1 10 12 IN 2 31. Actuator control 3/2 valve 32. 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 2 10 12 3 1 33. 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 12 3 2 1 10 34. 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 2 10 12 3 1 35. 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 desired results for the instroke speed 2 10 12 3 1 36. 3/2 valve actuator control 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 2 10 12 3 1 37. 3/2 valve actuator control 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 2 10 12 3 1 38. 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 2 10 12 3 1 39. Actuator control 5/2 valve 40. 5/2 Valve actuator control 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 - 14 + 4 2 5 1 3 12 41. 5/2 Valve actuator control 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 - 14 + 4 2 5 1 3 12 42. 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 - 14 + 4 2 5 1 3 12 43. 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 - 14 + 4 2 5 1 3 12 44. 5/2 Valve actuator control 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 - + 4 2 5 12 1 3 14 45. 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 - + 4 2 14 12 5 2 10 12 + 1 3 3 1 2 10 12 - 3 1 46. 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 - + 4 2 14 12 5 12 + 3 2 1 1 3 2 10 12 10 - 3 1 47. 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 - + 4 2 14 12 5 2 10 12 + 1 3 3 1 2 10 12 - 3 1 48. 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 - + 4 2 14 12 5 2 10 12 + 1 3 3 1 2 12 - 3 1 10 49. 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 - + 4 2 14 12 5 2 10 12 + 1 3 3 1 2 10 12 - 3 1 50. 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” + a1 A 4 2 14 12 5 2 10 12 + 1 3 3 1 2 10 12 - a1 3 1 51. Fully-automatic control - + a0 a1 A 4 14 2 12 5 1 3 2 10 12 Run/End 3 12 a0 3 1 2 1 10 2 10 12 a1 3 1 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 52. Sequential control 53. Circuit building blocks a0 A a1 b0 b1 B Run/End 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 54. 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- DA- B+ C- A+ B- C+ C+ A+ B- C- A- B+ 55. Repeat pattern sequence a0 a1 b0 A b1 B Run/End b0 b1 a1 a0 The two cylinders A and B are to perform a simple repeat pattern sequence as follows: A+ B+ A- BApply 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 56. Repeat pattern sequence a0 a1 b0 A b1 c0 B C Run/End c0 c1 a1 a0 b1 b0 For three cylinders A, B and C also to perform a simple repeat pattern sequence as follows: A+ B+ C+ A- B- CApply the rule “The signal given by the completion of each movement will initiate the next movement” c1 57. Non-repeat pattern sequence a0 a1 b0 A b1 B Run/End a0 b0 a1 b1 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- 58. Opposed signals a0 a1 b0 A b1 B Run/End a0 b0 a1 b1 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- 59. Mechanical solution a0 a1 b0 A b1 B Run/End a0 b0 a1 b1 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 60. 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 electromechanical relays PLC. The standard solution for medium to complex sequential systems (except where electrical equipment cannot be used) 61. 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- ATwo 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 Group l 14 Select l Group ll 4 5 2 12 1 3 Select ll 62. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 63. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 64. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 65. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 66. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 67. Cascade (two group) a0 a1 b0 A b1 B b0 a1 Gp l Gp ll Sequence Gp l A+ B+ Gp ll B- ARun/End a0 b1 68. 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 Gp l 4 14 2 10 12 Sel l 12 5 Run/End 3 1 Gp ll 2 1 3 Sel ll 69. Cascade building blocks This three group building block establishes an interconnecting pattern that can be extended to any number of groups Gp l Run/End Gp ll Sel l Sel ll Gp lll Sel lll 70. 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+ a1 in x a1 in y A+ in Group x A+ in Group y a1 Note: can often be rationalised to less than these three components 71. 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- ASelect 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 72. Three position valves 73. 5/3 Valve 5/3 valves have a third mid position The valve can be tristable e.g. a detented lever operator or monostable 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 4 2 14 5 1 3 14 4 2 12 12 5 1 3 14 4 2 5 1 3 12 74. 5/3 Valve actuator control 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 4 14 2 5 1 3 12 75. 5/3 Valve actuator control 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 4 14 2 5 1 3 12 76. 5/3 Valve actuator control 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 4 14 2 5 1 3 12 77. 5/3 Valve actuator control 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 4 14 2 5 12 1 3 78. 5/3 Valve actuator control 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 4 14 2 5 1 3 12 79. 5/3 Valve actuator control 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 preexhausted when changing from the mid position 14 4 2 5 1 3 12 80. 5/3 Valve actuator control 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 14 4 2 5 1 3 12 81. Logic functions for poppet and spool valves