A coupler, or coupling, is a device for joining rail vehicles in a train.
There are two different kinds of couplers in the units: Automatic couplers on both unit ends (driver cab car), which permit the coupling with another unit, and semi-permanent couplers, which permit a permanent connection between cars forming a unit.
There are 3 very general types of couplers used on railways worldwide:
1- Manual Couplers with manual only mechanical, pneumatic, and electric connections.
2- Semi-Automatic Couplers with automatic mechanical connection, but manual only pneumatic and electric connections.
Semi-permanent coupler is designed to ensure a permanent mechanical and pneumatic connection between the different cars that make up the unit. It does not need to be uncoupled unless there is an emergency or when in a maintenance workshop.
Both the coupling and the uncoupling of the semi-permanent couplers are carried out manually, and must be carried out with both cars still.
The semi-permanent coupler has a vulcanized metal-rubber articulation that allows relative movement between the cars. This coupler allows the coupled cars to resist both horizontal and vertical bends, as well as rotational movements.
One of the two couplers between cars is provided with an energy absorption device that absorbs the stresses transmitted from the carbodies.
3- Automatic Couplers with fully automatic mechanical, pneumatic, and electric connections.
Automatic coupler is in charge of mechanically coupling two units, by means of a simple approximation at a recommended speed of 5 km/h, and without the need of manual assistance.
The electric and pneumatic connection of the units is carried out automatically at the same time as the mechanical coupling.
This coupler allows the coupled units to resist both horizontal and vertical bends, as well as rotational movements.
Uncoupling of the units is also automatic. It is carried out from the driver’s desk, although in case of emergency it can be carried out manually by means of an uncoupling handle.
The automatic coupler is provided with an energy absorption device that collapses under strong impacts, hence protecting the cars frames.