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Railway coupling
A coupling or coupler is a mechanism, typically located at each end of a rail vehicle, that connects them together to form a train. The equipment that connects the couplers to the vehicles is the draft gear or draw gear, which must absorb the stresses of the coupling and the acceleration of the train.
Throughout the history of rail vehicles, a variety of coupler designs and types have been developed worldwide. Key design considerations include strength, reliability, easy and efficient handling, and operator safety. Automatic couplers engage automatically when the cars are pushed together. Modern versions not only provide a mechanical connection, but can also couple brake lines and data lines.
Different countries use different types of couplers. While North American railroads and China use Janney couplers, railroads in the former Soviet Union use SA3 couplers and the European countries use Scharfenberg and screw couplers. Challenges and complications arise when coupling vehicles with different couplers. Barrier cars, also called match cars, cars with dual couplers, or adapters are used to accomplish this task.
Compatible and similar couplings or couplers are frequently referred to using widely differing make, brand, or regional names, or nicknames, which can make describing standard or typical designs confusing. Dimensions and ratings noted in these articles are usually of nominal or typical components and systems, though standards and practices also vary widely with railway, region, and era.
Buff: when the consist (one or more cars coupled together) of cars is in compression; opposite of tension.
The basic type of coupling on railways following the British tradition is the buffer and chain coupling. A large chain of three links connects hooks on the adjoining wagons. These couplings followed earlier tramway practice but were made more regular. Buffers on the frame of the wagon absorbed impact loads, as the train overran a slowing locomotive.
The simple chain could not be tensioned, and this loose coupling allowed a great deal of back and forth movement and bumping between cars, as well as jarring when trains started. While acceptable for mineral cars, this coupling made for an uncomfortable ride in passenger coaches, so the chain was improved by replacing the center link with a screw with a left-hand thread on one side and a right-hand thread on the other. In the center of the screw is the handle housing with a hinged ball handle attached. This turnbuckle style arrangement allows the vehicles to be pulled together by tightening the screw with the attached handle. Typically, the screw is tightened until there are two threads left next to the handle housing. A support is attached to the trunnion nut on the coupling link side to rest the handle of the screw to prevent loosening of the screw while the coupling is in use. The official name of this type of coupling is screw coupling or UIC coupling according to the European standard EN 15566 Draw gear and screw coupling.
A simplified version of this, quicker to attach and detach, still used three links but with the centre link given a T-shaped slot. This could be turned lengthwise to lengthen it, allowing coupling, then turned vertically to the shorter slot position, holding the wagons more tightly together.
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Railway coupling
A coupling or coupler is a mechanism, typically located at each end of a rail vehicle, that connects them together to form a train. The equipment that connects the couplers to the vehicles is the draft gear or draw gear, which must absorb the stresses of the coupling and the acceleration of the train.
Throughout the history of rail vehicles, a variety of coupler designs and types have been developed worldwide. Key design considerations include strength, reliability, easy and efficient handling, and operator safety. Automatic couplers engage automatically when the cars are pushed together. Modern versions not only provide a mechanical connection, but can also couple brake lines and data lines.
Different countries use different types of couplers. While North American railroads and China use Janney couplers, railroads in the former Soviet Union use SA3 couplers and the European countries use Scharfenberg and screw couplers. Challenges and complications arise when coupling vehicles with different couplers. Barrier cars, also called match cars, cars with dual couplers, or adapters are used to accomplish this task.
Compatible and similar couplings or couplers are frequently referred to using widely differing make, brand, or regional names, or nicknames, which can make describing standard or typical designs confusing. Dimensions and ratings noted in these articles are usually of nominal or typical components and systems, though standards and practices also vary widely with railway, region, and era.
Buff: when the consist (one or more cars coupled together) of cars is in compression; opposite of tension.
The basic type of coupling on railways following the British tradition is the buffer and chain coupling. A large chain of three links connects hooks on the adjoining wagons. These couplings followed earlier tramway practice but were made more regular. Buffers on the frame of the wagon absorbed impact loads, as the train overran a slowing locomotive.
The simple chain could not be tensioned, and this loose coupling allowed a great deal of back and forth movement and bumping between cars, as well as jarring when trains started. While acceptable for mineral cars, this coupling made for an uncomfortable ride in passenger coaches, so the chain was improved by replacing the center link with a screw with a left-hand thread on one side and a right-hand thread on the other. In the center of the screw is the handle housing with a hinged ball handle attached. This turnbuckle style arrangement allows the vehicles to be pulled together by tightening the screw with the attached handle. Typically, the screw is tightened until there are two threads left next to the handle housing. A support is attached to the trunnion nut on the coupling link side to rest the handle of the screw to prevent loosening of the screw while the coupling is in use. The official name of this type of coupling is screw coupling or UIC coupling according to the European standard EN 15566 Draw gear and screw coupling.
A simplified version of this, quicker to attach and detach, still used three links but with the centre link given a T-shaped slot. This could be turned lengthwise to lengthen it, allowing coupling, then turned vertically to the shorter slot position, holding the wagons more tightly together.