Hello folks. I have a question for the German train experts. I noticed that the Sbahns like the br 425 or 423 have a main air line display, but it is not filled (5 bar) do they run without compressed air? Thanks.
As opposed to what? 5 bar is still ~73psi which is plenty, and most German electric locos and EMUs blend in a significant portion of dynamic brakes to supplement the air.
No, I meant that the pressure gauge (which should normally show 5 bar when the brakes are released) is at zero. That means they stay at zero, even if I brake or release. I'm assuming these trains don't use compressed air? (Br 425, 423, 422)
I noticed that too. And it seems to be correct. I attached a cab ride video featuring a BR 423 that shows the gauge for the HLL (Hauptluftleitung = brake pipe, far right) at zero during stops and running alike, whereas the brake cylinders (gauge to the right of the speedometer) get pressure during stops (to hold the train in place apparently, especially when the doors are open): (Didn't know before that they run underground on LZB, as it seems, btw). On the wikipedia page for the BR 422, 423 and 425 you can read that "Betriebsbremsungen" (regular brake applications) are performed using "elektrodynamische Bremsen" (dynamic brakes) (only). I assume that during regular operation the pressure in the brake cylinders is regulated electronically (ep-brake) and the HLL only exists as a backup system. If anyone has better intel, I would love to listen and learn..
Many thanks for the answer. That's exactly what I suspected and did a little research. I got the same result. Supposedly they only use compressed air when they are being towed, for example, outside of normal operation.
They still use compressed air and they wouldn't get brake release without it, as the parking brakes would remain applied (they're spring loaded and when air is in the main reservoir it holds the spring off). At higher brake demand the train will use blended braking which makes use of both dynamic and friction braking.
