Pneumatics
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Transcript

  • 1. Pneumatics
    • Pneumatic functions are very similar to electrical functions in many ways.
    • Compressed air ‘flows’ in a similar way to electric current.
    • Various hardware devices act like switches, or other electrical devices, to control the ‘flow’
  • 2. Pressure
    • Pressure determines the amount of force that is applied.
    • In very simple terms, it can be considered similar to current.
    • The higher the current, the greater the power.
    • The higher the pressure, greater the power.
  • 3. Flow
    • Flow determines the speed of pneumatic systems.
    • In very simple terms, it can be considered similar to dc voltage.
    • The higher the voltage, the faster the dc machine will operate.
    • The higher the flow, the faster the pneumatic operation.
  • 4. Pneumatic Components
    • Many simple pneumatic components can be compared to simple electrical components.
  • 5. Pressure Regulator
    • Reduces a high input pressure to a lower working pressure
    • Provides a steady output, despite changes in the input pressure
  • 6. Pressure Regulator
    • In many ways this can be compared to a voltage regulator or zener diode.
  • 7. Non-Return Valve (Check valve)
    • Allows air to flow in one direction, but blocks it from flowing back in the opposite direction.
  • 8. Non-Return Valve (Check valve)
    • In many ways it can be compared to a diode.
  • 9. Solenoid Valve
    • When electrical current is applied to a coil, the valve operates and allows air to flow.
    • Can be both Normally Closed (NC) or Normally Open (NO)
  • 10. Solenoid Valve
    • In many ways this can be compared to a contactor.
  • 11. Shuttle Valve
    • Allows air to flow to an outlet, from either of two inlets.
    • Blocks air from flowing from one inlet to the other
  • 12. Shuttle Valve
    • In many ways this can be compared to a diode bridge.
  • 13. Timer
    • Has a delayed action, after receiving a compressed air signal
    • Available in delayed-on or delayed-off formats
  • 14. Timer
    • Can be very closely compared with an electrical timer.
  • 15. Air Preparation
    • Usually consists of a filter, a regulator, a pressure gauge and a lubricator.
    • The filter removes moisture and debris.
    • The regulator and pressure gauge set a constant working pressure.
    • The lubricator injects an oil mist to help lubricate the moving parts of the system.
  • 16. Filter, Regulator & Lubricator
  • 17. Pneumatic Operation
    • Operation from the control cabinet in the crane
    • For a simple pneumatic spreader
  • 18. The solenoid valve energises and passes air to activate the Air Operated Valve
  • 19. The Air Operated Valve allows air to flow from the main line to the hooks Even when the push-button is released and the solenoid valve de-energises
  • 20. After a set delay, the timer activates and passes air to reset the Air Operated Valve The Air Operated Valve, closes, vents the line and cuts the air to the hooks
  • 21. Pneumatic Operation
    • Operation from the manual push-buttons on the side of the frame
  • 22. The manual valve closes and passes air to activate the Air Operated Valve
  • 23. The Air Operated Valve allows air to flow from the main line to the hooks Even when the push-button is released
  • 24. After a set delay, the timer activates and passes air to reset the Air Operated Valve The Air Operated Valve, closes, vents the line and cuts the air to the hooks
  • 25. Pneumatic Operation
    • Meanwhile, the amount of air in the air tank is going down.
  • 26. 8 bar 3 bar
  • 27. 7 bar 3 bar
  • 28. 5 bar 3 bar
  • 29. 5 bar 3 bar The differential pressure switch detects the falling pressure in the air tank.
  • 30. 3 bar 4 bar The contacts close, which causes the compressor to start and begin to refill the air tank .
  • 31. 5 bar 3 bar
  • 32. 6 bar 3 bar
  • 33. 7 bar 3 bar When the air tank is topped up to full pressure, the differential pressure switch detects this.
  • 34. 8 bar 3 bar The contacts open, which causes the compressor to stop.
  • 35. 8 bar 3 bar A non-return valve between the compressor and the air tank stops air from leaking back out from the air tank.
  • 36. Separate left and right release
    • Some of the pneumatic circuit is duplicated.
    • There are now two solenoid valves, one for releasing each side of the frame.
    • The example shown is one of the more complex designs.
  • 37. Solenoid 1 energises to release left hooks
  • 38. The solenoid remains energised by an electrical timer
  • 39. After a time delay, the solenoid de-energises and the air is vented.
  • 40. To release the other side, solenoid 2 energises.
  • 41. After a time delay, the solenoid de-energises and the air is vented.
  • 42. The manual release passes air to the timer, which then activates the air-operated solenoid
  • 43. When the pneumatic time delay is completed, the air signal to the air operated valve is cut.
  • 44. The return spring inside the air operated valve, closes the valve & cuts the air to the hooks
  • 45. “ Nagesco” Frames
    • These frames use a slightly different operating system.
    • All circuits operate at 110v.
    • There are Normally Open & Normally Closed solenoid valves
    • The release timing is via delay timers on the push-buttons.
  • 46. Nagesco Frames
    • Frame is marked with red & blue sides.
    • Control box has a 3-position switch:
    • Blue, ALL, Red
    • There is a single release button (with delay-off timer)
  • 47. Left & right solenoids are normally open type Main solenoid is energised and passes air through the open solenoids to the hooks
  • 48. Main solenoid is energised and passes air through the open solenoids to the hooks
  • 49. Push-button time delay expires and solenoid de-energises and vents line, causing hooks to lock
  • 50. Push-button time delay expires and solenoid de-energises and vents line, causing hooks to lock
  • 51. To release ‘blue’ side only, solenoid ‘R’ is energised which closes the flow to hooks on the ‘red’ side.
  • 52. The main solenoid is energised and air flows to the hooks on the ‘blue’ side only.
  • 53. So what can go wrong?
    • As you can see, the electrical and pneumatic circuits are quite simple so what can go wrong with these spreaders?
    • Well, not a lot really.
    • The cause of most faults are air leaks or failed electro-mechanical timers.
  • 54. Electrical Faults
    • Failed compressor.
    • Defective or wrongly adjusted pressure switch.
    • Blown fuse or tripped circuit breaker (sometimes resulting from impact).
    • Failed transformer
    • Loose wiring
  • 55. Electrical Faults
    • Defective electro-mechanical timer unit.
    • Wrong control box being used
    • Defective gantry cable
    • Water in power socket or damaged power socket.
    • Damaged control socket or plug
  • 56. Pneumatic Faults
    • Defective compressor
    • Defective or wrongly adjusted pressure regulator.
    • Damaged pneumatic hose to hook.
    • Defective hook (stuck or seal failure)
  • 57. Pneumatic Faults
    • Water in pneumatic system (drain tanks & check filter)
  • 58. Pneumatic Faults
    • The following is a common scenario:
    • All hooks unlock but will not re-lock
    • The compressor is running
  • 59. Pneumatic Faults
    • This is nearly always due to an air leak in the pneumatic system or because the release has been operated soon after the spreader was powered up.
  • 60. Pneumatic Faults
    • Check the air pressure on the main air cylinders.
    • Is it less than 3 bar?
    • If yes, then you probably have a large air-leak. The air is leaking out as fast as the compressor tries to fill the tanks.
  • 61. Pneumatic Faults
    • Some spreaders have a valve on the outlet from the tanks – close the valve and see if the air pressure in the main cylinders starts to rise.
    • Locate the air leak and repair it.
    • When the pressure has returned to around 5 or 6 bar, open the valve
  • 62. Pneumatic Faults
    • If there is no valve on the outlet of the main air cylinders-
    • Remove power to the spreader.
    • Repair the air leak
    • Restore power to the spreader.
    • Wait for the pressure in the main cylinders to rise to around 5-6 bar.
  • 63. 2 bar 2 bar A serious air leak will cause pressure in the main cylinders to fall below 3 bar.
  • 64. 2 bar 2 bar Below around 2 bar there is not enough pressure for the pneumatic timer to activate and reset the system
  • 65. 2 bar 2 bar Therefore the hooks will remain open and the leak will prevent the cylinder pressure from rising, despite the operation of the compressor