Vertical caving terminology and methods > General hardware
A wheel ("sheave") that the rope can run over, providing much less friction than if it just runs through a carabiner. In site of their benefits in many situations, it is more common to simply run the rope through a carabiner, and pulleys are generally reserved for a few specific uses. There are several variations, including dedicated pulleys with a housing that can be clipped to a carabiner, down to a basic wheel that is put onto an oval carabiner, using the carabiner as its axle. Most designs have to be removed from the carabiner they are attached to, in order to connect or disconnect them from a rope, and a keeper cord may be needed to avoid dropping them. Some have fixed sides, where the rope needs to fit through the gap between them, so they need to be used with a wide carabiner which pulls equally on both sides, so they work best with an oval carabiner. Many use swing cheeks, where the two sides can be rotated separately, allowing them to be separated to get the rope between them, and these tend to have no gap when closed, so they can work with almost any design of carabiner. Lightweight, small designs are often preferred, but the strength requirements may sometimes mandate larger pulleys. Some designs have a cam like an ascender which allows the rope to move only in one direction, specifically for use with hauling, and are known as progress capture pulleys. Many of these can also be used as an ascender.
A pulley may be used to allow an object to move along a relatively straight rope with reduced friction, such as for crossing a Tyrolean traverse, or as part of a chest roller. In these cases, the rope remains still, and the load is attached to the pulley with a pull direction roughly perpendicular to the rope.
A pulley can also be used for redirecting a force, such as for hauling equipment, top roping, the double bungee variation of rope walking, part of a Z-rig tensioning system, and as part of a rope washer. In these cases, the pulley is attached to a fixed object, one or both ends of the rope are pulled, and the rope changes direction at the pulley.
A pulley can be used as a force multiplier, doubling a pulling force at the expense of halving the distance moved (or vice versa, but they are rarely used that way). They are used this way with the Italian technique, Z-rig tensioning systems, and various types of improvised rescue. In these cases, the pulley is attached to a moving load, the rope changes directions at the pulley, and one end of the rope is pulled, while the other is fixed. Various configurations, such as redirecting the fixed end back to the load, can then be used to give 3 or more times the force, or pulleys can be stacked to double an already doubled force.
Pulleys can also be used to share a load equally between two anchors. For this, the two ends of the rope are fixed to anchors, the rope is given an amount of slack, and the load is connected to the moving pulley. The pulley will move along the rope until the force applied to each anchor is the same. This has traditionally been used to hang a ladder on the middle of a rope stretched over a pitch, to create the effect of a Y-hang. However, it lacks redundancy, and a failure of either anchor causes the ladder to fall, so this approach is not recommended.
Efficiency of pulleys plays a major role in how useful they are, especially when they are being used in Z-rigs and other force multiplier situations (see that section for some practical measurements). A pulley with perfect efficiency (something that cannot actually exist) would be able to redirect a force completely. If using a pulley with a terrible efficiency of 50%, pulling on one end of the rope with 10 kg would cause only 5 kg to be seen by the rope on the other side of the pulley. 35-45% is the approximate efficiency of a carabiner, so a pulley with an efficiency of 45% is basically pointless, as it could be replaced with a simple carabiner. An efficiency of 70% is fairly standard for pulleys without ball bearings (they use a low friction "bushing" instead), while extremely good pulleys with ball bearings and a large sheave tend to have an efficiency of about 90% (manufacturers may claim higher, but actual testing generally gives 85-90% for the best pulleys). These efficiencies are reduced when mud is involved, and generally get worse over time, with bushings normally wearing out faster than sealed ball bearings. Efficiencies are normally measured as the proportion of force that can be redirected by a 180° deflection (so the rope changes direction by 180° at the pulley), and the pulley's sheave must always perform a full 360° rotation during testing, just in case it has some rough spots. The efficiency is normally 1-5% higher for a 90° deflection (it does not follow a simple mathematical formula, since it relates to the friction of the rope, pulley surface and pulley bearings). With no deflection (meaning that the pulley is not involved at all), the efficiency is 100%.
Pulleys were used in 1991-1802 BCE in Egypt, though these were fairly crude, with ropes running over a grooved stone cylinder, and could not be connected to objects as needed. They were used for construction, so that people standing on a flat surface could haul something up a sloped surface. Pulleys were used to raise containers of water by the Sumerians in Mesopotamia in 1500 BCE. They were depicted in Assyria in 900-800 BCE, as a wheel used to redirect a rope that lifted a bucket of water. It is not known exactly when these developed into self-contained units. Archytas devised the mathematics that showed how to multiply forces using pulleys in 400 BCE, in what was then Greece, now Italy. Archimedes demonstrated their use as a force multiplier in Greece between 265 to 214 BCE, using compound pulleys to allow a single person to move a ship, and to allow cranes to lift a ship. He is credited with making the first block and tackle. During the middle ages, their use expanded along with the rise in sailing. In 1321-1337, a pulley is thought to have been first used to access a cave now called Covolo di Butistone in Verona, now Italy. It was being used as a fortress, rather than for active cave exploration, but this is the earliest known use of a pulley for accessing a cave. The pulley was described in 1664, but will have been needed from whenever the winch was installed, or perhaps even earlier. Pulleys also formed an integral part of many winches, and so they will have been used in many caves, such as in 1595 by guano miners at the Gouffre de Padirac. However, this section will concentrate on pulleys that are separate from a winch's own structure. It is unknown when cavers and miners first started using pulleys in caves, but the first written record is from 1682, when British captain Greenville Collins explored Pen Park Hole using ropes and sailor's pulleys. A British team consisting of John Birkbeck, William Metcalfe, William Howson and 7 others used pulleys to help lower cavers from the British Long Churn into Alum Pot in 1847. In 1851, a pulley was used on a wooden structure to winch Colombian priest Romualdo Cuervo 115 metres down into Hoyo del Aire. By 1852, steeplejacks were using a type of progress capture pulley which they called a brake block or brake pulley, which could be used when being hauled up a structure, in case the person hauling accidentally let go. A specific design used by James Duncan Wright, better known as Steeple Jack, in 1852 was stated as being a "pulley [...] connected [to] a sort of handle, which acts, when pressed to the cord, with the same effect as a brake", showing that it could also be manually activated. Later designs were patented. An American design from 1873 used a wedge that would slide under the rope and jam it into the housing of the pulley when it was turned in the wrong direction. An American patent from 1888 shows a pulley with a one-way cogwheel on the side of the wheel, with a sprung lever that jams against the teeth when it is pulled in the wrong direction. The lever can be disengaged by hand. It is not known when this approach was first used with a pulley, but it is likely to be much older, since similar mechanisms are seen on medieval winches and weapons. This would not be as effective as a modern progress capture pulley, since it would just act as a static bar instead of a pulley, creating a little more friction, so the 1888 patent shows another part of the lever jams the rope against the pulley, just like a modern progress capture pulley. French caver Édouard-Alfred Martel initially used a log laid across a pitch as a very poor pulley for a winch in 1889. However, at some point before 1892, he switched to using an A-frame leaned over the pitch, holding an actual pulley. In 1892, he also used pulleys for a pull-through with a ladder in Aven de Vigne Close. The Kyndwr Club descended Eldon Hole using a boatswain's chair lowered on a rope fed through a pulley, in 1900. Cavers were using pulleys for vertical caving in 1935 in the Grenoble region of France, with French cavers Bouffé and Perche from the Lyons Speleo Club using one in the Dent de Crolles system. One was used as part of a maypole described by French caver Henry P. Guérin in 1944, in the same area. He also showed their use with ladders to create the equivalent of a Y-hang. French caver Pierre Chevalier describes their use for pull-up cords in 1946. Bruno Dressler made dedicated caving pulleys in the Grenoble region of France in the 1960s, before giving the design to Fernand Petzl, who probably started making them in 1968 (before Petzl existed as a company).
This history section only covers pulleys. This article also has a detailed history of many of the other devices and techniques that are used for vertical caving.
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