What are they and what do they exactly do? I heard that the NBÜ/ep switch controls the passenger emergency brakes and the el/pn probably switches between electric and pneumatic braking, but I'm unfamiliar with the operation of these.
There are places on the railway where it is not appropriate for an emergency train to stop, tunnels, bridges, embankments where there is no access for rescuers. This NBU switch sets the mode when the emergency brake is not activated. When the passenger applies the emergency brake in the tunnel, the brake is activated only behind the tunnel. The individual modes are how the train will communicate with the system on the railway line.
el / pn - braking mode Selector switch for the operating mode of the driver's brake valve • el = electronic • pn = pneumatic
Modern passenger cars have electronically controlled brake valves. On the wagons that support it is the brand of el. Communicate the electronics with the locomotive. Other wagons have brake valves controlled by a drop in air pressure in the main line. In this case, pn.
Newer coaches use electrically initiated brake systems. Older coaches and freight wagons use pneumatically (air) initiated systems.* The switch is set according to what the loco is pulling. To date the only German passenger coaches modeled are 4th-generation Dostos, which are electric. *El systems are still ultimately pneumatic, using air pressure to apply the brakes. But whereas the old way is to actuate the brakes by decreasing the pressure in the brake pipe, a daisy-chain of hoses connecting all the cars, some modern rolling stock dispenses with that (which can be rather slow to propagate to the back of the train), and uses electronic relays instead so that all cars' brake application is more or less simultaneous
Thank you, Until read your explaination do I understand it's Electronically controlled pneumatic brakes, some of other threads mistake it to the pneumatic and electric brake itself
Whilst enough people have answered your question I want to bring in a little more information: ep-switch: The ep-switch is there to turn off the electro-pneumatic brake. The indirect ep-brake, which can be found on locomotives and coaches, is used to have better and faster control over the brakes. Modern air brakes have an actuation speed of ca. 250-280m/s. That means that on trains like the DB IC, the last coach would start braking roughly 1s after you started braking in the front. That can lead to an uncomfortable ride and hurt the braking performance of the entire train. Therefore modern rolling stock has an indirect ep-brake. To use the ep-brake you'll also need a reservoir pipe (HBL) to feed the brake pipe (HL) locally. Via two valves and a control unit, every coach is now capable of releasing or feeding air into the brake pipe. So the actuation time is now reduced from depending on the distance to the brake valve, to the short actuation time of the distributing valve of each coach. When the driver puts the brake valve into a certain position, this information is transmitted via the data line (ISL) to the control unit, which then releases or feeds air to the brake pipe. If you put the switch into "pn" the ep-brake is disabled and the brakes will function like a normal train brake. NBÜ-switch: The NBÜ (Notbremsüberbrückung) is the emergency brake override, used to prevent trains from stopping in tunnels or other places on the network that are dangerous for a train and its passengers when evacuating. There are multiple different variants of the NBÜ, hence the selector switch. As the UIC hadn't standardized a system yet, DB developed its own system in the 1980s, which used the already cramped 18-pin UIC line. Then the UIC standardized the ep-brake line and also introduced their NBÜ system. Both of the systems mentioned above were actual overrides: When the emergency brake was pulled, the train applied full braking force and only released the brakes if the driver used the override. That changed with the new NBÜ 2004, also developed by DB, where the emergency brake no longer directly causes a full application, but rather sends an alarm to the cab. If the driver doesn't respond with either an emergency brake application or an override himself, the emergency brake is activated normally. This system was later adopted by the UIC. Whilst both UIC standards use the same ep-line to communicate between the cab and the vehicles in the train, the protocols and pin assignment are incompatible between the two systems. That's why there is a switch to change between those systems.
