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WSR Couplings
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 • How couplings work...
Screwlink, Threelink, Instanter and Buckeye. No, not the well known company of solicitors, but the main methods of coupling railway rolling stock together. On the West Somerset Railway all of the above four named types are used. I will endeavour to describe the different types and how they operate without baffling you with too much technical jargon. In order for two railway vehicles to be connected together in a train they are all provided with some form of a coupling device, which is both strong and practical. As the old saying goes, a chain is only as strong as its weakest link. The same can be applied to the couplings on a train of any description.
Jon Tooke unravels the mysteries of couplings and explains how the vehicles in the train are kept together. Jon is a regular Guard on the Railway.and also took the pictures below. Jon Tooke
 • Three Link Coupling
This type of coupling is exactly what it says - a set of three links that are hung from draw-hooks on each vehicle.
On each end of each piece of rolling stock, amongst all the other components, there will be a draw-hook and a three-link coupling. One end of the three-link coupling is permanently fixed under the draw-hook, and the other end is free. When one piece of rolling stock is to be coupled to another, the free end of the three-link coupling will be dropped over the draw-hook on the next vehicle, and so on along the length of the train.
Therefore, every vehicle will be coupled to the next by using only one of its own three-link couplings, and one of its own draw hooks.
Because there was always going to be a certain amount of slack in the coupling, the two vehicles could move freely in-between the coupling, and this resulted in the once familiar clanging noise as the buffers came together as a train either sped up or slowed down.
The three-link coupling was very common in railways early days, but has been superseded. Today, the three-link coupling is found on older goods wagons, see picture for an example of the three-link coupling.
Three Link Coupling
 • Screw Coupling
This is a development of the 3-link coupling. To overcome the slack in the three-link coupling, a screwed thread replaces the middle link. By winding the weighted adjustment bar around the threaded screw, this would be take up any slack between the two end links. The adjustment bar is weighted at one end so that it will always hang downwards when not being used. When the threaded screw is tightened sufficiently, the two vehicles will be bought together so that their buffers just touch. This would then act so as to provide for cushioning by compressing the side buffers. Today, screw couplings are used in-between a locomotive and the rolling stock, in-between the coaches and power cars on the DMU, and on goods stock. Please see picture for an example of a screw link coupling.
Screw Link Coupling
 • Instanter Coupling
Another development of the three-link coupler is the "Instanter" coupler.
Rather than a middle link or a threaded adjustable screw, the middle link is forged into a triangular shape with a keyhole shape in its middle, to allow the distance between vehicles to be (crudely) adjusted. This is to allow the side buffers used with the coupler to be adjacent to each other and provide some degree of slack cushioning.
As shown in the picture, the Instanter is in the slack position and is ready for uncoupling.
When running, the Instanter will have the top part of the keyhole uppermost which will be holding the two links in a tighter position to that shown.
Instanter couplings are found on goods wagons.
As with all the above three different sorts of couplings, to either couple or uncouple the vehicles, a skilled person, either a guard or a shunter, had to get down on the track between the two vehicles and lift the coupling chain over the hook of the other vehicle. Sometimes a specially designed "shunting pole" was used for quickly uncoupling freight wagons. Please see the picture for an example of a Instanter coupling.
Instanter Link Coupling
 • Buckeye Coupling
By far the most common coupling seen around today, both on the WSR and on the mainline railway, is the Buckeye coupling. This is an automatic, mechanical coupler of a design originating in the USA, It was invented in 1879 by a US civil war veteran named Eli Janney. The term Buckeye comes from the nickname of the US state of Ohio "the Buckeye state" and the Ohio Brass Co. which originally marketed the coupling. Rather than using links or screwed devices, the Buckeye coupling itself is simple. It consists of four main parts, a cast steel coupler head containing a hinged jaw or "knuckle", the hinge pin, about which the knuckle rotates during the coupling or uncoupling process and a locking pin. The locking pin is lifted to release the knuckle. It does this by raising a steel block inside the coupler head that frees the locking pin, which is lifted to release the knuckle.
When coupling two coaches together, the Buckeye couplings have to be in the "up" or horizontal position to receive each other, and at least one of the jaws MUST be open. When the two coaches come together, the jaws of the two Buckeyes close around each other and will stay coupled together.
To uncouple one Buckeye from another, a chain is pulled to the side of the coupling which releases the block inside the coupler head, by moving the locking pin, this unlocks the coupler and allows the jaws to open on that particular Buckeye.
However, if a locomotive is to be attached to the coach, the Buckeye coupling MUST be in the "down", or vertical position because the locomotive will be coupled using the screw link coupling from itself to the draw-hook on the coach. Please see the pictures for examples of the Buckeye coupling.
Whether a Buckeye coupling be up or down, a securing pin slots through it to stop it swinging about, or, if in the up position, to hold it in that position. The securing pin has a hinged "tell tail" on the end of it which will always fall downwards to stop the pin vibrating out of place.
Buckeye couplings are found on all the WSR coaching stock. A complete Buckeye coupling weighs some 14 stone, and there is a certain technique used to move the Buckeye from the horizontal to the vertical position.
Buckeye Coupling
 • In conclusion...
Jon adds "I hope that you have you find this brief insight into couplings interesting and educational, and next time you visit the WSR, you’ll know exactly what that funny piece of metal is called at the end of a vehicle!".
This page is not from the official West Somerset Railway website   
© Stephen Edge