DIFFERENT TYPES OF COUPLERS IN RAILWAYS:
In order for two railway vehicles to be connected together in a train they are provided with couplers. Since there are a large number of railway vehicles which might have to be coupled at one time or another in their lives, it would seem sensible to ensure that the couplers are compatible and are at a standard position on each end of each vehicle.
There are a variety of different couplers around. However, there is a high degree of standardization and some common types have appeared around the world.In order for two railway vehicles to be connected together in a train, they are provided with couplers.
Since there are a large number of railway vehicles which might have to be coupled at one time or another in their lives, it would seem sensible to ensure that the couplers are compatible and are at a standard position on each end of each vehicle. There are a variety of different couplers around. However, there is a high degree of standardization and some common types have appeared around the world.
Link and Pin:
The simplest type of coupler is a link and pin. Each vehicle has a bar attached to the center of the headstock (the beam across the end of the vehicle, variously called the end sill or pilot in the US) which has a loop with a center hole attached to it.
Each coupler has a bell mouth around the end of the bar to assist in guiding the bar with the hole into place. The loops are lined up and a pin dropped into them. It’s not very sophisticated but it was used for many railways during the 19thcentury and has persisted on a few remote lines to this day. The narrow gauge Alishan Railway in Taiwan is one such line.
Bar:
The next type of coupler is the bar coupler. This is what is known as a semi-permanent coupler. It cannot be disconnected unless the train is in a workshop and access underneath the train is available. It is normally used in EMUs which are kept in fixed formations of two, three or four cars.
The bar couplers are located within the unit, while the outer ends of the unit have some type of easily disconnected coupler. Bar couplers are simple, just consisting of a bar with a hole at the inner ends through which the car body is connected by a bolt. Others consist of two halves which are just bolted together.
3-Link Coupling:
This type of coupling is exactly what it says -a set of three links which are hung from hooks on each vehicle. A development of this is the “Instanter” coupler, which has a middle link forged into a triangular shape 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.The coupler required a person to get down on the track between the two vehicles and lift the coupling chain over the hook of the other vehicle. Sometimes a “coupling pole” was used for quickly uncoupling freight wagons
Screw Coupler:
This is a development of the 3-link coupling where the middle link is replaced by a screw. The screw is used to tighten the coupling between the two vehicles so as to provide for cushioning by compressing the side buffers. In addition to the mechanical couplings required to connect the vehicles, trains had to have connections for brakes, lighting, and heating. All the work involved in connecting the two vehicles was carried out manually.
Buckeye/Knuckle Coupler :
By far the most common coupler seen around the world is known variously as the”Knuckle”, “Buckeye” or “Jenney” coupler. This is an automatic, mechanical coupler of a design originating in the US and commonly used in other countries for both freight and passenger vehicles. It is standard on the UK hauled passenger vehicles and on the more modern freight wagons.
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 coupler. It was invented in ]879 by a US civil war veteran named Eli Jenney, who wanted to find a replacement for the link and pin couplers then standard in the US.
Link and pin coupler required staff to stand between cars to couple and uncouple and there were many injuries and even deaths as a result. Jenney’s invention solved these problems and was taken up by a number of lines. The device eventually became standard when the link and pin coupler was banned by the US government in 1900.The coupler itself is simple.
It consists of a cast steel head containing a hinged jaw or “knuckle”.The coupler () is made of cast steel and consists of four main parts. The head itself, the 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 which frees the knuckle and allows it to rotate.
To couple two vehicles, the knuckles must be open. When the two vehicles are pushed together, the knuckles of the two couplers close on each other and are locked from behind by a vertical pin dropping a steel block into place behind a raised casting on the knuckle. To uncouple, one of the pins must be pulled up to release the block locking the knuckle. This is done by operating a lever or chain from the side of the vehicle.
Fully Automatic Couplers:
More and more railways are using fully automatic couplers. A fully automatic coupler connects the vehicles mechanically, electrically and pneumatically, normally by pushing the two vehicles together and then operating a button or foot pedal in the cab to complete the operation. Uncoupling is done by another button or pedal to disconnect the electrical contact and pneumatic connection and disengaging the coupler mechanically.Fully automatic couplers are complex and need a lot of maintenance care and attention.
They need to be used often to keep them in good working order. IR passenger stock is mostly built with side buffers and screw couplers that have to be manually connected. The recently acquired Alsthom coaches have CBC (centre-buffer-coupler).All new freight stock and container rake wagons for CONCOR, have CBC couplers. But there are still some older freight cars which have hook couplers with side buffers, as well as many with screw couplers.
There is also a ‘transition’ coupler, which has a CBC mechanism for coupling to other CBC couplers, but which also has a central screw coupling provision which allows it to be coupled to wagons which do not have CBC. There are two side buffers provided as well.
These were useful when CBC couplers were just being introduced and there was a lot of freight stock that had screw couplers, but it has now gradually lost its importance as more and more of the freight stock is fitted with CBC couplers. These days only locos and brake vans tend to have transition couplers.Locomotives have transition couplers to allow them to hook up to either CBC or screw-coupled stock, and they also have side buffers.
EMUs use Scharnberg couplers which are a center buffer type which automatically connects the electricity and air links as well. The coupler face is rectangular (from above) and has semicircular ends. A large pin project from the end of the coupler, which mates with a corresponding hole in the coupler of the other car. DMUs also use these couplers with regular twin brake pipes; although in some cases (e.g. Jallandhar DMUs) they are modified to have different brake hoses than the integrated ones that are part of the couplers. In IR parlance, these couplers are called ‘Shaku’ couplers.