Vertical caving terminology and methods > Personal SRT gear
An unusual type of ascender that is not designed to be used for prusiking, and is instead designed to be used as a safety brake when abseiling. However, it gets used for many other purposes, often against the manufacturer's recommendations. It moves when the body of the device is pushed, but not when the device's lever is pulled downwards, known as a lever cam ascender. This is an approach used by much older ascenders, where the weight of the user is what causes the rope to be gripped, instead of a rotating eccentric cam. A shunt traps the rope against the front of the device when the lever is pulled, while almost all traditional lever cam devices trap the rope against the back of the device. Shunts are not designed for caving, and are aimed more at climbing. All attachments must be removed from a shunt in order to remove it from a rope, meaning that it can easily be dropped by mistake at a rebelay. The way to avoid this is to attach a keeper cord the smaller attachment loop, and tie it to yourself, meaning that there is now some string to add to your spaghetti. The device may not function well on muddy ropes, but is intended to work well enough on frozen ropes.
Intended to be used as a safety brake when combined with a descender, and may sometimes be used with a figure of 8 descender, or more rarely with other descenders that leave one hand free to hold the Shunt. It does this much better than most lever cam devices because it uses a smooth bar to contact the rope, and is unlikely to snag the rope unintentionally while descending. This allows a second point of contact to the rope while descending, offering redundancy for safety purposes. For this to work, it requires the body of the device to be pulled downwards to release it while descending, and during an emergency, it requires the presence of mind to release the device so that it can catch the fall, something that is very hard to do when it actually happens. The Shunt is normally attached to the up rope above the descender, but can be used extremely clumsily on the down rope below it instead. Sometimes used for self belaying, since it does not cause as much damage to the rope as most other ascenders would do when catching a fall. In fact, it will slip on the rope a little, adding some shock absorbtion. However, due to the way a fall can pull the Shunt in an unexpected manner, it can end up oriented in a way that causes the lever cam not to engage at all, or to release the rope completely, so that it will not succeed in catching the fall. These issues are far less likely on most dedicated fall arresters. It is important to note that even though it is used to catch falls, as an ascender and as a safety brake, the official Petzl Shunt is not classified as PPE.
In 1904, a lever cam device was patented by Austrian locksmith Michael Gayer, which he called a "clamping sleeve for climbing devices". This was sold as a "climbing device" by F. Turczynski Jagd- und Touristen-Asrüstingen, a mountaineering shop in Vienna, Austria, the city where Austrian mountaineer Karl Prusik lived, run by a member of the Wiener Alpenklub (Vienna Alpine Club), which Karl Prusik was also a member of. The design had a very limited range of rope sizes which it could work with, and used a fiddly bolt and wing nut to close a hinged section around the rope, which would have been very easy to drop by mistake. It was advertised as a fall arrester in Austrian mountaineer E. Fink's Touristen-Vademekum publication in 1904, for self belaying when climbing up or down, for climbers, quarry workers, miners, construction workers, roofers and plumbers. German mountaineer H. Sixt proposed a lever cam device, which German mountaineer Franz Kröner then improved and manufactured in 1911, called a "climbing lock". It was intended to be used in the same way as a Shunt, though its lever worked slightly differently. Austrian mountaineer Karl Prusik claimed in 1931 that the "climbing locks" could not be used when the ropes swelled because they got wet. The Shunt was first sold by Petzl in 1972 as an emergency backup device for use on frozen ropes, and the design has been virtually unchanged since then.
This history section only covers the Shunt. 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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