Part III: What’s the difference between screw coupling and Digital Automatic Coupling?

01. 06. 2021

Digital Automatic Coupling represents a revolution in European rail freight transport.

In our new series "DAC FAQs", we answer the most important questions about this new technology in the rail freight industry!

In the third part of our series, we have answered the most important questions about the differences between screw coupling and DAC4 for you.

Screw coupling (SC)

  • High manual and time-intensive work
  • Manual coupling and uncoupling
  • Entering the space between the buffers (known as the “Berner Raum” in German) is required (danger zone!)
  • No power lines or data cables
  • Difficulty recruiting shunters

Digital Automatic Coupling (DAC) with integrated power lines and data bus cables (level 4)

  • Automatic coupling using air pipes, power lines and data cables
  • Simplified uncoupling using a rope hoist (partially automated)
  • Sufficient power supply and secure data cables
  • Enables further automation and digitisation of operational procedures such as the train integrity monitoring, automatic brake test, and Wagon order capture
  • Electro-pneumatic brakes (simultaneous braking) can be used
  • Improves Operational Health & Safety
  • Increases productivity

Where have all the buffers gone?

In order to prevent damage to wagons during shunting, they are equipped with what are known as side buffers.  When DAC comes into play, the buffers and the danger zone in the space between them are no longer an issue. As a form of middle buffer coupling, the buffers in a DAC are integrated into the coupling as a spring & damping device.

Are different types of coupling systems compatible with each other?

The different coupling designs are not compatible with each other because each coupling head has a different structure. This is also why the European rail freight transport sector has to agree on one specific coupling design before all trains can be retrofitted.

Which DAC prototypes are currently available?

Are the prototypes fully compatible with the conventional push-pull system (screw coupling)?

DAC is set to replace screw coupling. Central buffer coupling does away with side buffers. The two systems are not compatible, so one system has to be phased in and the other one phased out simultaneously.  Initial simulations of this were carried out in the migration strategy funded by the German BMVI (German Federal Ministry of Transport and Digital Infrastructure). At RCG, we are checking these scenarios and simulations as part of the group-wide TARO project funded by the BMK and FFG. In Europe, these are evaluated at a higher level as part of the European DAC Delivery Program.

Will the maximum load on the DAC be equal to, higher than, or lower than the draw hook load?

Level 4 DACs differ according to pressure and tension. According to the specifications, they can withstand greater loads than conventional screw coupling.

What does the coupling process look like?

As part of the funded TARO project – funded by the Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK) and the Austrian Research Promotion Agency (FFG), the RCG is working on processes that will help it get “DAC ready”.

In the next part, you’ll find out more about the DAC prototype tests!