In
railroad
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a prep ...
ing, slack action is the amount of free movement of one car before it transmits its motion to an adjoining coupled car. This free movement results from the fact that in railroad practice cars are loosely coupled, and the
coupling is often combined with a shock-absorbing device, a "
draft gear", which, under stress, substantially increases the free movement as the train is started or stopped. Loose coupling is necessary to enable the train to bend around curves and is an aid in starting heavy trains, since the application of the locomotive power to the train operates on each car in the train successively, and the power is thus utilized to start only one car at a time.
United Kingdom
The UK formerly used
three-link coupling
Buffers and chain couplers (also known as "buffers and screw", "screw", "screwlink", and "English" couplers) are the de facto UIC standard railway stock coupling used in the EU and UK, and on some surviving former colonial railways, such as in ...
s, which allowed a large amount of slack; these were soon replaced on passenger stock by
buffers and chain couplers where the couplings are held tight by buffers and shortened by a turnbuckle while in most other parts of the world automatic couplings, such as the
Janney coupler and the
Scharfenberg coupler, were adopted from the late Nineteenth Century on. Three-link couplings are a rarity in modern use.
Gallery
File:Consett-tankwagon41 - buffer beam.jpg, Three-link coupling on an antique tank wagon
Image:Railroad coupler.agr2.jpg, AAR
AAR or Aar may refer to:
Geography
* Aar, a river in Switzerland, tributary of the Rhine
*Aar (Lahn), a tributary of Lahn river in Germany, descending from the Taunus mountains
* Aar (Dill), a tributary of Dill river in Germany, also in the bas ...
Type E couplers on flatcar
A flatcar (US) (also flat car, or flatbed) is a piece of rolling stock that consists of an open, flat deck mounted on a pair of trucks (US) or bogies (UK), one at each end containing four or six wheels. Occasionally, flat cars designed to carry ...
s
File:Carrage couplings on ABT Railway (3939380014).jpg, Screw-tensioned three-link coupling, shown attached but not yet tensioned; when tightened, the turnbuckle draws the buffers together, eliminating jarring and shocks when starting or slowing the train. The narrow buffers of the left-hand vehicle are sprung, the thicker buffers on the right contain a hydraulic damper. The sprung buffers allow for some train articulation even when the cars are drawn firmly together
See also
*
Draft gear
References
Rail technologies
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