| Technical Articles | Pulleys & Systems for Rescue & Industrial Rope Access
Victims in the field of rescue often times find themselves stranded somewhere well above head level on cliffs, mountains, bridges, buildings and other structures. The obvious challenge of importance to the rescue attempt is the need to get the victim down. Any ultimate benefit from the rescue maneuver hinges upon this one factor. Without success here there is no success and there is no rescue.
How does one go about getting the victim down? Sheer brute strength can serve the purpose however it is not always practical. Trekking an extended distance while supporting another can result in the dreaded sewing machine knee and/or the burning of the quads, neither of which is an enjoyable side-effect the day after. Outside of helivacs, pulleys and pulley systems offer the ideal solution for getting the victim down in the remote access areas often presented to rescue teams.
When it comes to pulleys the force of gravity can be used to assist in the work while the use of friction on a rope is used to control that force. Gravitational forces and the friction used to control a descent are the integral principles of a rescue technique. This harnessing of the power of both the force of gravity and the control factor of friction can reduce the need for manpower and equipment while allowing for a system in which things move quickly to evacuate the patient package in timely descent.
However, down is not always the path of least resistance or the quickest route to the rescue termination. Moving the victim up may sometimes be necessary, prudent and expedient particularly when the vantage point of additional rescue resources mandates an attack from above rather than below. In a rescue strategy of upward evacuation the forces of gravity can work against the team's effort; but even so, in many cases there are effective methods by which the overall effort invested into the rescue can be greatly minimized.
So how does a team overcome the gravity working against the upward direction of such a rescue? Just as pulley systems are the ideal solution for getting the victim down, so too they are the answer here. The various ropes and pulleys incorporated into pulley systems are the preferred, lightweight option to counteract these forces of gravity when working in remote areas. To help compensate for the many variables, obstacles and challenges thrown at a team in the field a thorough assemblage of pulley system components along with a thorough knowledge and understanding of the principles of pulley systems and mechanical advantage will go a long way in preparing the appropriate logistical solution of attack.
The history of the development of civilization is chock-full of examples of men working with their hands using simple, compound and complex pulley systems. A system of tools so simple was at the core of powering the industrial revolution that set America on the road to resources development and economic power. The simple tools that proved so beneficial to our predecessors will likewise serve well those brave men and women rushing to the heights to the aid of the unfortunate, stranded victim.
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The usefulness of pulley systems extends well beyond simply the lifting of the rescue package:
- LIFTING the rescue package is what first comes to mind
- LOWERING under control (river rescue)
- SMALL JIGGERS(adjunct tasks, scoops, pick offs, etc.)
- LINEAR ANCHORS (between anchor points called pretensioned backties)
- GUYING of artificial high directionals at the edge
- APPLYING-HOLDING TENSION
- POSITIONING within space
In addition to lowering load packages pulleys are used to haul a load upward and to move objects in any direction and many times their use incorporates a multiplicity of directions of movement such as in the raising/lowering of a person in a rescue situation. Some pulleys have an integrated rope clamp to make certain tasks easier. Certain pulleys also allow for movement along a rope or cable, again… for moving loads or evacuating a person. Tower Rescue, Confined Space Rescue and Industrial Rigging are excellent examples of this…
Pulley systems for hauling, lowering and holding require a very clean working knowledge of the equipment needed and the challenge that is presented. Some examples can be seen in the following videos…
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An optimum advantage of comprehending pulley systems is the fact it frees the rigger to assemble the system specific to the need. The following are key considerations before building a pulley system:
- Hauling area — What space is available for the hauling team?
- Throw length — What is the throw length? Is it sufficient?
- Haulers present (input) — How many haulers are available for the task to be undertaken?
- Load to be lifted (output) — The actual mass to be lifted: Climbing, rescue or extreme rescue load. Highline tensioning?
- Rope needs — How much rope is available for the pulley system you intend to construct?
- Equipment needs — How much equipment is available for the task you intend to undertake?
- Hauling area incline — Can you pull downhill? Wouldn’t you rather?
- Adaptability — Can you easily change the mechanical advantage?
- Resetting — Resetting can use valuable time & energy. Does the pulley system minimize this?
- Lowering ability — Can the pulley system lower easily under control? Also, will it respond quickly? River rescue? Live bait?
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Simple, Compound, & Complex Pulley Systems
- SIMPLE: The rope is tied to either the load or the anchor and is run alternately through pulleys on the load or the anchor until the loose end finds itself in the grasp of the pullers.
- COMPOUND: A simple pulley system pulling on the end of a simple pulley system. (Each simple system is referred to as a component of the sum. May be more than two components)
- COMPLEX: A pulley system that is neither simple or compound.
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An established nomenclature serves to keep everyone on the same page in terms of what words are used for communication in any given system of specificity. Definitions of the words used within any nomenclature are key to insuring everyone using it is speaking the same language. Some of the terms in the nomenclature listed here may vary from terms you have used to describe the same principle.
- PULLEY: A small grooved wheel used with a rescue rope to change the direction and point of application of a pulling force and in combination (as in pulley system) to increase the applied force especially in a raising operation.
- PULLEY SYSTEM: An assemblage of rope and pulleys used to increase the force to the level required for the lifting or tightening to be undertaken.
- CHANGE OF DIRECTION: A pulley on the anchor closest to the haulers (cd or cod). A cd adds no mechanical advantage to the system.
- DIRECTIONAL: A Pulley or pulleys between the pulley system and the load to be raised (d). Both low and high directionals are common. Not to be confused with a change of direction.
- GANGED PULLEY SYSTEM: Any pulley system which is attached by a haul grab to a second main rope for the purpose of lifting or lowering a load.
- IN LINE PULLEY SYSTEM: A system where the rope lifting or lowering the load and pulley system are one and the same.
- THROW: The available distance between maximum pulley system extension and two-block (Note: Simple pulley systems have only one throw. Compound pulley systems have a minimum of two throws)
- HAUL FIELD: The available distance a hauler or haulers can run out or the space that they have to stand and pull
- HAUL GRAB: The rope grab closest to the load in any pulley system throw or compound pulley system component throw
- PIGGYBACKED: A compound pulley system with like same components. Example: (2:1) (2:1) (2:1)= 8:1 piggyback (3:1) (3:1)= 9:1 piggyback
- TWO BLOCK: The point at which the throw of any pulley system or pulley system component is collapsed. Also known as Chock-o-block
- RESET: The act of extending the pulley system throw out after “two block”
- RATCHET: The progress capture device allowing resetting of the pulley system after two block
- RATCHETMAN: A person who tends the ratchet for up or down on the pulley system
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Acronyms (Used for pulley system notation and written communication)
||Progress capture device (Ratchet)
||Ideal mechanical advantage
||Practical mechanical advantage
|Abt or PTBT
||Pretensioned backtie (Non Working)
||Ratchet prusik (Type of PCD)
||Ratchet camming device (Type of PCD)
||Change of direction
Rock Exotica's Aztek Pulleys are Perfect for the Job
Every aspect of the Aztek pulleys has been optimized for the job. They have built-in swivels. There is no conventional becket because that would give an unwanted increase in length. Instead the rope end is held on the side of the pulley so the pulleys can be pulled very tightly together when needed in operaton or for storage. The two pulleys are different colors to match up with their attendant Prusiks. The Prusiks are quickly activated with a quick release pin. Of course, the sheaves are all ball bearing.
Complete system with two Aztek pulleys, main rope (8 or 9mm), two Prusiks and a travel restrict Prusik.
While using a complete system is highly recommended, the pulleys are available separately for those building their own system.
Strength as a system, even with 8mm rope, is 36kN.
Here is a compact mechanical advantage system that continually amazes rescuers with its many uses and versatility.
Some of the uses are as a pick off, travel restrict, adjustable directional, high directional guyline, high angle attendant tether, high angle litter scoop, load release hitch and much more. Both Aztek pulleys have their own color-coded Prusik and can be easily activated or deactivated. This means you can have the ratchet at either the top pulley or the bottom pulley. The special 3 on 2 Prusik cannot come off the rope, so the deactivated Prusik will stay ready to be used as soon as you need it. Complete systems use sewn Prusiks and a sewn eye on the main rope, which makes things neater and more compact than knots. You cannot appreciate how smooth and easy use of the Prusiks is until you experience it. Because the Prusik only sees a fraction of the total load in an MA system, they don't get too tight and they are easy to release and very controllable.
This system grew out of extensive use and experimentation of small MA systems. It is light years ahead of anything else. If the world as we know it ends and you need an MA system to help you rebuild civilization, this is the one.
Pulley Systems in Petzl Confined Space Diagram
Pulleys in Petzl Rescue Evacuation Diagram
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