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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Lifting the rescue package
Lowering under control
Small jiggers for pick offs
Pretensioned backties
Pulley Systems - Uses
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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
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Hauling area & incline
Throw length
Number of haulers
Load to be lifted
Pulley Systems - Considerations
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Hauling area & incline
Throw length
Number of haulers
Load to be lifted
Equipment needed
Pulley Systems - Considerations
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Hauling area & incline
Throw length
Number of haulers
Load to be lifted
Equipment needed
Resetting
Pulley Systems - Considerations
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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 reset 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
 Differential pulleys can balance out
differences in rope stretch and pulling
speed
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
T
T
Pulley Systems – “T” Method
• Ts adds together at junction points
2T
T
T
3T
T
T
2T
Pulley Systems – “T” Method
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Simple, compound, complex?
Total MA?
Name?
Input force?
Pulley Systems – “T” Method
Pulley Systems – “T” Method
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Simple, compound, complex?
Total MA?
Name?
Input force?
Pulley Systems – “T” Method
Pulley Systems – “T” Method
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Simple, compound, complex?
Total MA?
Name?
Input force?
Pulley Systems – “T” Method
Pulley Systems – “T” Method
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Simple, compound, complex?
Total MA?
Name?
Which anchor point should be
the strongest?
• Input force?
Pulley Systems – “T” Method
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 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
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