Pulley Systems v Pulley Systems Uses Lifting the

Pulley Systems

v. Pulley Systems - Uses • Lifting the rescue package

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

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

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

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

v. Pulley Systems - Considerations • Hauling area & incline

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

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

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

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

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

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

v. 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

v. 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

v. 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%

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

v. 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

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

v. 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

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

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

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

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

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

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

v. 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

v. 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 = 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

v. 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

v. 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

v. Pulley Systems – “T” Method • Assumes no loss from friction or ideal mechanical advantage

v. 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

v. 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

v. 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

v. 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

v. 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

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

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

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

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

v. Pulley Systems – “T” Method T

v. Pulley Systems – “T” Method T T

v. Pulley Systems – “T” Method T T T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method 2 T T T 2 T

v. Pulley Systems – “T” Method 2 T T T T 2 T

v. Pulley Systems – “T” Method 2 T T T T 2 T 2 T

v. Pulley Systems – “T” Method 2 T T T T T 2 T 2 T

v. Pulley Systems – “T” Method 2 T 2 T T T T T 2 T 2 T

v. Pulley Systems – “T” Method • • Simple pulley system Total MA is 5 Name would be (5: 1)s Input force is 1 T 2 T 2 T T T T 5 T T 2 T 2 T

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

v. Pulley Systems – “T” Method T

v. Pulley Systems – “T” Method T T T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method T T T 2 T 2 T

v. Pulley Systems – “T” Method T T T 2 T 2 T 2 T

v. Pulley Systems – “T” Method T T T 2 T 2 T 2 T 4 T

v. Pulley Systems – “T” Method T T 2 T 2 T 2 T 4 T

v. Pulley Systems – “T” Method 4 T T T 2 T 2 T 2 T 4 T

v. Pulley Systems – “T” Method • • Compound pulley system Total MA is 6 Name is (2: 1)(3: 1)c Input force is 1 T 4 T T T 2 T 2 T 2 T 6 T 4 T

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

v. Pulley Systems – “T” Method T T T

v. Pulley Systems – “T” Method 2 T T

v. Pulley Systems – “T” Method 2 T T T

v. Pulley Systems – “T” Method 2 T T T 2 T

v. Pulley Systems – “T” Method T 2 T T T 2 T

v. Pulley Systems – “T” Method 3 T T 2 T

v. Pulley Systems – “T” Method 3 T T 3 T 2 T T T 2 T

v. Pulley Systems – “T” Method 3 T T 6 T 3 T 2 T T T 2 T

v. Pulley Systems – “T” Method • Complex pulley system • Total MA is 5 • Name shorthand does not work for a complex system • Input force is 1 T 3 T T 6 T 3 T 2 T T T 5 T 2 T

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

v. Pulley Systems – “T” Method T T T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method T T T 2 T

v. Pulley Systems – “T” Method 2 T T T 2 T

v. Pulley Systems – “T” Method 2 T T T 2 T T

v. Pulley Systems – “T” Method 2 T T T 2 T T 3 T

v. Pulley Systems – “T” Method 2 T T T 2 T 3 T

v. Pulley Systems – “T” Method 2 T T T 2 T 3 T 6 T T 3 T

v. Pulley Systems – “T” Method 3 T 2 T T T 2 T 3 T 6 T T 3 T

v. Pulley Systems – “T” Method 3 T 2 T T T 2 T 3 T 6 T

v. Pulley Systems – “T” Method 3 T 2 T T T 2 T 3 T 6 T 12 T T 3 T 6 T

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

v. 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%

v. 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

v. 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

v. 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

v. Pulley Systems – Ideal and Real MA • Example using an assumed input of 100 lbs and a pulley efficiency of 90% 139 66 73 81 73 410 171 90 81 100 90 100 190 154