Buffers and chain coupler

The screw coupling, clutch or even UIC UIC standard clutch, the clutch is used in most European railway vehicles. In contrast to modern clutches the screw coupling can only transmit tensile forces and must be connected or released by hand.


Each fitted with screw couplings car has a hook, on which hangs the tab. At their turn is movable with a nut, the spindle attached to the clapper. On the spindle is attached with another mother of the bracket. All connections can be rotated to the track about axes transverse, the bracket about the axis in the longitudinal direction of the track. With the clapper, the spindle can be rotated, comprising on the one hand and left-hand threads on the opposite side of a right-hand thread, which are designed as a round thread. By rotating the spindle, the distance between the two nuts is shortened or lengthened. This process is briefly turn in the railroad jargon and called long turn.

For connecting two vehicles the bracket is hooked in the coupling hook of the adjacent wagon, and the connection by rotation of the spindle by means of the clapper briefly rotated until the buffer can be easily pressed. After turning short stay on both sides of the spindle free each not exceeding two threads between the nut and threaded collar of the spindle. The engine supports the operation of coupling by during which presses against the train - called press in technical language. In addition, depending on the type of vehicles even electrical cables and pneumatic hoses of the brakes must be connected.

For coupling a railway staff under the page buffer has to pass into the center of the track to rise to perform the work. This process involves a number of accidents due to the cramped conditions and is especially dangerous in snow and ice. To enable the work to be kept free of the space between the vehicles is defined as the Bern area. The climbing in and out between the vehicles is facilitated by the handles under the page buffers.

A properly connected screw coupling results in a play-free connection between the vehicles, which is under a slight bias. If the clutch screws are not short rotated sufficiently, this can lead to some violent jerking in front pulling part, especially if in the first phase of braking the rear pulling part runs on the front, or pushed trains. When is too much play, it can also come to break the selfsame due to the sudden load on the clutch.

Normal screw couplings have to re- set in -use vehicles according to TSI WAG have a breaking load of 850 kN. Previously, a breaking load of approximately 700 kN was common, so screw couplers are resilient only at low route gradient with a maximum of 4000 t train mass or about 550 kN tensile load during service. For heavier trains other couplings must be used or an intermediate or helper locomotive is required. For the heavy ore trains between the North Sea ports and steel mills Peine -Salzgitter, for example, special cars were purchased with particularly reliable automatic couplings design Unicupler, and converted a number of locomotives of the series 151 accordingly.

For railcars, which are only coupled to each other, to have automatic central couplings such as enforced the Scharfenberg coupler.

In Poland, a semi-automatic screw coupling was developed. You allowed with a guide and two pneumatic actuators catch the clutch bracket, to allow lift and attach it to the tow hook. Two degrees of freedom of the system allow the coupling of two rail vehicles in the curve. To use the semi-automatic screw coupling used by train drivers or the switchyard control buttons, which are usually attached to the vehicle front sides of the locomotive.


With the screw coupler beginning of the 20th century, the chain couplings previously used were replaced, which could not withstand the higher trailer loads. To simplify the work, there has been since the Second World War, several plans to replace the clutch screws on all cars with automatic couplers. Many modern vehicles, all built in principle since the mid-1960s, are prepared for this change constructively. Due to technical and especially financial difficulties and because it was at the time of the opinion that such change in the whole of Europe would have to take place simultaneously, but everything remained the same, and it is also not expected that the screw coupling medium actually another by a system will be replaced. The Mixed clutch that easily enables a coupling between vehicles with screws and SA-3 and UIC central buffer coupling was, at the time only allowed in shunting. In Finland, Mixed coupling was used early on in normal operation, even for the coupling of passenger trains. In the meantime, Unilink and Transpact central buffer couplings have been developed with integrated dome chain with the types that do not require additional Mixed coupling devices more.

Coupling failure

Breakthrough of the coupling occurs even today occasionally Zugtrennungen ( as on December 8, 2007 with a Regional-Express DB AG in Furth, see ERI 2/2008 p.54). As a result of tearing off the main air line both train parts are then automatically braked. Dangerous is the train separation for travelers who happen to be at the interchange. It is also possible the two train parts collide due to different braking behavior, especially when the rear pulling part has its own driving power features ( or second locomotive hauled train ).

After a train separation, the sections may be reconnected, as each car has at each end of the car a full clutch ( hook and screw ), of which only one item ( hook or screw ) is required during operation. Detachable connections of the main air line and the main air reservoir pipe is duplicated so that the train after re- domes can continue driving, provided that no further damage has occurred.