Hi, all. I'm a bit confused about something. My understanding is that modern train braking systems are based on an original design by Westinghouse back in the 1800s. These systems are "fail safe" systems in that air pressure is applied to reservoirs to actually release the brakes rather than to apply them. This means that if the brake system runs out of air, the brakes apply fully rather than release, which allows the system to "fail safely." In game, though, it appears that the brakes work in the opposite way. The cylinder pressure increases, which applies the brakes. Is my understanding just wrong, or are modern train brakes not actually fail safe systems based on the Westinghouse design? https://en.wikipedia.org/wiki/Railway_air_brake
I'm wondering if my confusion comes from the fact that the locomotive uses direct air brakes (where pressure applies the brakes) but the cars use the failsafe system. We obviously aren't seeing a pressure gauge from the cylinders on the cars... EDIT: Ah, this might explain why when you apply the brakes (at least on the German trains I'm driving) you see the cylinder pressure increase, but the brake pipe pressure decreases. Maybe the locomotive brakes (being direct air brakes) are applied by increasing pressure, but the brakes on the cars are applied by dumping pressure from the brake pipe to atmosphere? This doesn't quite mesh with something I recall hearing Matt say in his YouTube talk on train brakes -- that often the brake pipe on American trains will leak, causing the brakes to release and allowing the cars to roll. It seems to me that a car disconnected from a brake pipe should have its brakes applied rather than released, right?
Alright: the brake cylinders do fill to apply pressure; but they fill based on a reduction in pressure in the brake pipe (the cylinder air is actually stored in reservoirs, with the connecting valves held closed by BP pressure.) Lowering the BP pressure (by lowering the pressure in the equalizing reservoir in the loco by way of the brake handle) causes some air pressure to vent into the brake cylinders, moving the pistons and thus the brake shoes. If the brake pipe empties completely (say a train separation, or a crewman hitting the emergency valve), the pipe dumps to atmosphere, the valves spring wide open and the reservoirs vent it all into the cylinders, slamming the brakes on.
Since the OP is talking about German trains, I would not recommend videos from a solely US-focused Youtuber like Hyce.
Ah, that makes sense! And also explains why repeatedly applying and releasing the brakes can run them "out of air" on American trains -- the reservoirs on the cars don't have enough time to fill up, so there's nothing to move into the cylinders even when the brake pipe pressure drops.
I'm pretty sure German trains use similar principles for their train brakes. I'm prepared to be wrong about that though...
Ah. The brake pipe is already empty (consequence of the pipe being disconnected and the valve left open). What is leaking there is the air in the brake cylinders, which aren't expected to restrain an unconnected car for days. Over ~12-48 hours depending on temperature and condition, the brake system will bleed out, which is why parked cars are "pinned" with handbrakes.
German trains use a more sophisticated system (before we even get to epü). The biggest difference is that German brakes can be partially released. That can't be done with a traditional Westinghouse triple valve, which can only be released completely and re-set.
The main difference between the US brakes and european is in the US it's a triple valve system, and in europe it's a Distributor system - triple valves don't support partial release while distributors do. I believe triple valves are simpler and cheaper? and given the number of US freight cars I suspect that's always been a driving force - plus having triple valves in a large amount of stock before distributors came along is probably a reason to continue with what you've got, stock interoperability is more important. The problem of brakes releasing is because of when you *dont* open the valves and do what's called "Bottling the Air". In this case you have a brake pipe that's at say 75psi at the point you cut the cars off, and before you did so you closed the angle LOVE to bottle the air on the cars. In theory, in a perfect system, the brake pipe will remain forever at 75psi, the brake cylinders will remain where they are and all are happy. TSW reflects that perfect world, for info. The reality however is that nothing is perfect. Each freight car has some equipment to help release the brakes faster to improve train handling. The danger here is that if there's a leak that lets air flow back from the emergency reservoir (which is at 90psi and thus greater than your 75psi brake pipe) into the brake pipe then the brake pipe pressure will slowly rise over time. After it's gone up by just 1.5 psi the accelerated brake discharge will then specifically open valves to let air from the emergency reservoir into the brake pipe to help the brake pipe recharge, this then means that other cars feel the increase to the brake pipe and gradually they each start pushing their emergency reservoir into the brake pipe and before long, the brake pipe is cheerfully back up to 90psi, the cars brakes are all released and... disaster awaits. Bottling the air is illegal by FRA laws. Any train left standing must be vented completely and maintained on its parking brakes. I *think* i've understood the process by which the incident happens, if not, it's something like that anyway For older cars that dont have the newer (1980's) ABDW valve, you dont have the quick release at 1.5 psi increase - but - that just means it'll take longer to happen, it'll still happen. I gather from reading online, some railroads will bottle air for short change-end manoeuvres but by and large the risks outweigh the benefits and it's usually a banned practice for any purpose. Matt.
Do you know of any sources on air brake distributor valves? I'm trying to improve the wikipedia article.
All I can suggest is googling phrases like "bottled air", "bottling the air" and "ABDW" - googling those got me some interesting reference to check what I was posting above. I am absolutely no expert on such things - but there are many out there on trainorders.com and other sites who are Matt.
Have you ever considered adding some advanced simulation to coupling systems overall, with controllable hoses and valves? It sounds like a logical step after brake controls were added to all wagons across the board in german content. And it would add so many new gameplay loops and fun to shunting, rather than just running around at 25 km/h but doing nothing otherwise. (I wrote a lengthy suggestion on this.)
US air brakes do seem to work differently, which is why you can hump shunt in Run 8 or you end up with runaway disasters like Lac Magantic in Canada. I also really need to spend time studying the differences!
You can hump shunt in Europe as well, it's the main way how trains are sorted. Some also do even more reckless things with unbraked trains, like bumping locos over the catenary border in Tarvisio. Until they once bumped it accidentally too much and it ran down the hill at 160 km/h..
If somebody is really interested into the workprinciples of a train brake system i recommend to study it while taking time. Also in my personal opinion its recommend to start on freight wagons before trying to study the pneumatic diagrams of a locomotive. The entire "fail safe" part is still depending on the knowledge and responsibility of humans. Below an example of ignored procedures and lack of understanding about train brake systems. 1: The brake test was not successfull (brakes were not releasing on the consist) 2: To "solve" the "problem", all wagons were vented until the entire reservoir / Chambers were empty and the brakes released 3: "Problem solved", due all 3 railwaymen on this ballast consist were killed, it was never clear another brake test was performed, but when looking at the top picture, its clear they didnt. 4: The ballast train was pushed downhill with only the locomotive brakes working. 5: A controlled derailment into a construction train was the least horrible scenario 6: The Brakes worked fine, the air connection handles between the Locomotive to the wagons were all closed. (No air could pass to the wagons) 7: A human mistake, which caused brakes not to release, was "solved" by making a death trap out of the consist.
