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Pulley Systems

Pulley Systems. Pulley Systems - Uses Lifting the rescue package. Pulley Systems - Uses Lifting the rescue package Lowering under control. Pulley Systems - Uses Lifting the rescue package Lowering under control Small jiggers for pick offs. Pulley Systems - Uses

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Pulley Systems

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  1. Pulley Systems

  2. Pulley Systems - Uses • Lifting the rescue package

  3. Pulley Systems - Uses • Lifting the rescue package • Lowering under control

  4. Pulley Systems - Uses • Lifting the rescue package • Lowering under control • Small jiggers for pick offs

  5. Pulley Systems - Uses • Lifting the rescue package • Lowering under control • Small jiggers for pick offs • Pretensioned backties

  6. Pulley Systems - Uses • Lifting the rescue package • Lowering under control • Small jiggers for pick offs • Pretensioned backties • Directionals

  7. Pulley Systems - Considerations • Hauling area & incline

  8. Pulley Systems - Considerations • Hauling area & incline • Throw length

  9. Pulley Systems - Considerations • Hauling area & incline • Throw length • Number of haulers

  10. Pulley Systems - Considerations • Hauling area & incline • Throw length • Number of haulers • Load to be lifted

  11. Pulley Systems - Considerations • Hauling area & incline • Throw length • Number of haulers • Load to be lifted • Equipment needed

  12. Pulley Systems - Considerations • Hauling area & incline • Throw length • Number of haulers • Load to be lifted • Equipment needed • Resetting

  13. Pulley Systems - Considerations • Hauling area & incline • Throw length • Number of haulers • Load to be lifted • Equipment needed • Resetting • Lowering ability

  14. Pulley Systems - Definitions • Sheave is the grooved wheel that the rope runs on • The larger the diameter of the sheave, the less friction and the more efficient • Usually made out of nylon or aluminum

  15. Pulley Systems - Definitions • Side Plate can have holes or not, and can swivel or not • Larger top attachment point allows for the use of larger or multiple carabiners

  16. Pulley Systems - Definitions • Bearing or Bushing are the points where the axle meets the other parts of the pulley • Bearings are more efficient than bushings • This pulley with bearings has an efficiency of 216% and with bushings it is 198%

  17. Pulley Systems - Definitions • Becket is a lower attachment point between the two sheaves • Can be used to attach a rope or a second pulley

  18. Pulley Systems - Definitions • PMP or Prusik Minding Pulley has side plates that help keep a prusik knot from being jammed in the pulley • The prusik knot has to be wider than the distance between the side plates

  19. Pulley Systems - Definitions • Directional is a pulley that is between the pulley system and the load • Does not add any MA to the system

  20. Pulley Systems - Definitions • Change of Direction is a pulley on the anchor that is closest to the haulers • Does not add any MA to the system

  21. Pulley Systems - Definitions • Pr is a ratchet prusik which is a type of progress capture device

  22. Pulley Systems - Definitions • Ph is a haul prusik for attaching to the rope

  23. Pulley Systems - Definitions • Collapsed Pulleys or Two Block is when the system can not be made any shorter

  24. Pulley Systems - Types • Simple is if all of the traveling pulleys move towards the anchor at the same rate of speed

  25. Pulley Systems - Types • Simple • Compound is any combination of two or more simple pulley systems acting on each other

  26. Pulley Systems - Types • Simple • Compound • Complex does not follow any of the rules for a simple or compound pulley system

  27. Pulley Systems - Types • Simple Pulley System Rules • The number of pulleys plus one equals the mechanical advantage (MA) • End of rope attached to the load means the MA is odd • End of rope attached to the anchor means MA is even • Cumulative friction from more than five pulleys significantly works against MA

  28. Pulley Systems - Types • Compound Pulley System Rules • Total MA equals the product of each simple pulley system’s MA (2:1 acting on 3:1 = 6:1) • The greatest MA created using the fewest pulleys comes from 2:1 acting on 2:1 (2:1 x 2:1 x 2:1 x 2:1 = 16:1) • Having the greater MA system acting on the lesser means less resets • Traveling pulleys move toward anchors, but not necessarily at the same speed

  29. Pulley Systems - Types • Compound Pulley System Rules • Compound systems need people at each reset prusik for fastest action • Anchors should be offset so that each simple system collapses at the same time

  30. Pulley Systems - Types • Complex Pulley System Rules • Determining total MA requires the use of the “T” method, which can also be used for simple and compound systems • Systems that have pulleys moving towards the load are complex • Differential pulleys can balance out differences in rope stretch and pulling speed

  31. Pulley Systems – “T” Method • Assumes no loss from friction or ideal mechanical advantage • Assumes that the rope angle through a pulley is very close to 180 degrees • Assumes the tension input on one side of a pulley equals the tension output on the other side of the pulley T=1 T=1

  32. Pulley Systems – “T” Method • Always assume that the tension (T) input is equal to 1, whether it is one person or a haul team T=1

  33. Pulley Systems – “T” Method • Trace the rope through the system and add Ts as the rope passes through a pulley or tension point T T T T

  34. 2T • Pulley Systems – “T” Method • Ts adds together at junction points T T T T 2T 3T

  35. Pulley Systems – “T” Method • Simple, compound, complex? • Total MA? • Name? • Input force?

  36. Pulley Systems – “T” Method

  37. Pulley Systems – “T” Method • Simple, compound, complex? • Total MA? • Name? • Input force?

  38. Pulley Systems – “T” Method

  39. Pulley Systems – “T” Method • Simple, compound, complex? • Total MA? • Name? • Input force?

  40. Pulley Systems – “T” Method

  41. Pulley Systems – “T” Method • Simple, compound, complex? • Total MA? • Name? • Which anchor point should be the strongest? • Input force?

  42. Pulley Systems – “T” Method

  43. Pulley Systems – Ideal and Real MA • Do you actually work less to move a weight using a pulley system? • Real world pulley systems lose efficiency through friction • 2” pulley with 7/16” rope has an efficiency of about 85% • 4” pulley with 7/16” rope has an efficiency of about 95% • Bushings have an efficiency of about 85% • Bearings have an efficiency of about 95%

  44. Pulley Systems – Ideal and Real MA • People are assumed to be able to pull about 50 pounds of force using gloved hands • Assuming a rescue load of 450 lbs and our “standard” 5:1 simple pulley system, it should only take 2 people to lift the load • 2 people pulling 50 lbs each is 100 lbs of force through a 5:1 pulley system generates 500 lbs of force • But, some is lost through friction at each pulley

  45. Pulley Systems – Ideal and Real MA • Assuming an IMA of 500 pounds, a loss of 90% per pulley results in 328 lbs of force • Further, assume a loss of 35% where the rope bends over an edge using the “ice tray” edge protection • It could be much greater for carpet or canvas • Our total force is now down to 213 lbs • So, using our normal raising system, we would need about 4 people to lift a rescue load

  46. Pulley Systems – Ideal and Real MA • What can improve the RMA? • Each person pulls more than 50 lbs • Edge friction is reduced • Use the most efficient pulley as close to the initial input as possible

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