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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

- Lifting the rescue package
- Lowering under control
- Small jiggers for pick offs
- Pretensioned backties

Pulley Systems - Uses

- Lifting the rescue package
- Lowering under control
- Small jiggers for pick offs
- Pretensioned backties
- Directionals

Pulley Systems - Considerations

- Hauling area & incline

Pulley Systems - Considerations

- Hauling area & incline
- Throw length

Pulley Systems - Considerations

- Hauling area & incline
- Throw length
- Number of haulers

Pulley Systems - Considerations

- Hauling area & incline
- Throw length
- Number of haulers
- Load to be lifted

Pulley Systems - Considerations

- Hauling area & incline
- Throw length
- Number of haulers
- Load to be lifted
- Equipment needed

Pulley Systems - Considerations

- Hauling area & incline
- Throw length
- Number of haulers
- Load to be lifted
- Equipment needed
- Resetting

Pulley Systems - Considerations

- Hauling area & incline
- Throw length
- Number of haulers
- Load to be lifted
- Equipment needed
- Resetting
- Lowering ability

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

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

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%

Pulley Systems - Definitions

- Becket is a lower attachment point between the two sheaves
- Can be used to attach a rope or a second pulley

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

Pulley Systems - Definitions

- Directional is a pulley that is between the pulley system and the load
- Does not add any MA to the system

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

Pulley Systems - Definitions

- Pr is a ratchet prusik which is a type of progress capture device

Pulley Systems - Definitions

- Ph is a haul prusik for attaching to the rope

Pulley Systems - Definitions

- Collapsed Pulleys or Two Block is when the system can not be made any shorter

Pulley Systems - Types

- Simple is if all of the traveling pulleys move towards the anchor at the same rate of speed

Pulley Systems - Types

- Simple
- Compound is any combination of two or more simple pulley systems acting on each other

Pulley Systems - Types

- Simple
- Compound
- Complex does not follow any of the rules for a simple or compound pulley system

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

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

Pulley Systems - Types

- Compound Pulley System Rules
- Compound systems need people at each haul prusik for fastest action
- Anchors should be offset so that each simple system collapses at the same time

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

Pulley Systems – “T” Method

- Assumes no loss from friction or ideal mechanical advantage

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

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

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

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

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

Pulley Systems – “T” Method

- Simple, compound, complex?
- Total MA?
- Name?
- Input force?

2T

T

T

T

T

T

T

T

T

T

2T

5T

2T

- Pulley Systems – “T” Method
- Simple pulley system
- Total MA is 5
- Name would be (5:1)s
- Input force is 1T

Pulley Systems – “T” Method

- Simple, compound, complex?
- Total MA?
- Name?
- Input force?

4T

T

2T

2T

T

T

T

2T

2T

2T

4T

6T

- Pulley Systems – “T” Method
- Compound pulley system
- Total MA is 6
- Name is (2:1)(3:1)c
- Input force is 1T

Pulley Systems – “T” Method

- Simple, compound, complex?
- Total MA?
- Name?
- Input force?

3T

2T

3T

T

T

T

T

T

T

2T

5T

- Pulley Systems – “T” Method
- Complex pulley system
- Total MA is 5
- Name shorthand does not work for a complex system
- Input force is 1T

Pulley Systems – “T” Method

- Simple, compound, complex?
- Total MA?
- Name?
- Which anchor point should be the strongest?
- Input force?

6T

2T

T

T

T

T

T

T

3T

2T

3T

6T

6T

12T

- Pulley Systems – “T” Method
- Compound pulley system
- Total MA is 12
- Name is (3:1)(2:1)(2:1)c
- The right anchor point should be the strongest since the force on it is 6T
- Input force is 1T

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%

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

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 25% 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 246 lbs
- So, using our normal raising system, we would need about 4 people to lift a rescue load

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

139

- Pulley Systems – Ideal and Real MA
- Example using an

assumed input of

100 lbs and a pulley

effeciency of 90%

90

81

66

73

100

81

90

100

73

190

410

154

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