German locomotives have two Notch 1 brake positions, 1A and 1B. From what I’ve read, and please correct me if I’m wrong, the driver goes straight into 1B and has 1A available as a partial release state. I’m wondering why the brake system is designed like this. I’m looking for real world context and use scenarios just to satisfy my curiosity. (If I had to guess, I’m gonna say it has something to do with the fluid dynamics that exist in a pneumatic brake system. Maybe the brake system needs a certain amount of pipe reduction before the brakes will apply, but the same restriction does not exist when you’re trying to release. Again, just a guess) Thanks!
When starting to brake, 1B is the first notch that does anything with the indirect brakes, it reduces the brake pipe pressure to 4.6 bar. This is to ensure that all brakes along the train register the pressure drop and start to brake. They only become active if a pressure drop is "large enough" over a certain amount of time. This guarantees that no brakes erroneously get stuck in running. When releasing you get 4.7 bar in notch 1A because the problem does not exist.
