Quacking Duck Posted February 4 Posted February 4 (edited) There are two brake-related buttons on the control panel of the Dragon 2 locomotive whose functions I do not understand. When the "brake releaser" button is pressed, it rapidly reduces the indicated brake cylinder pressure to 0, but only while it is pressed. When the button is released, brake cylinder pressure returns to approximately its original level. I had originally assumed that this button could accelerate the process of releasing the train's brakes. However, using this button while the brakes are releasing, after having charged the brake pipe to above 5 bar, does not appear to accelerate brake release in any useful way. It appears that there is a "true" level of brake cylinder pressure which can only decrease slowly. When the button is released, indicated brake cylinder pressure returns to that level. Under what circumstances, if any, does this button actually help to release the brakes? Toward the right side of the control panel, near the brake gauges, there is a "brake assimilation" button. Pressing it has no obvious effect. What does this button do, and under what circumstances is it used? Edited February 4 by Quacking Duck 1
jeroezie Posted February 4 Posted February 4 The brake releaser do only work on the locomotives brakes. With old stock, like EU08, EP08 etc. this drains air from a very slow filling reservoir, so the effect will last long. On more modern stock such as Br 186 and dragon locomotives, it drains the locomotives brakes only when being actually pressed. The brake assimilation increased the brake line pressure from 5,0 bar to 5,4 bar. This is to deal with pressure differences in the brake pipe. It will also ensure all triple valves (this valve translates the brake pipe pressure to cylinder pressure that goes to the actual brakes) have an adequate pipe pressure, so they release the brake full, even if they are overcharged (for example by a previous pressure spike). The brake assimilation or fill position, depending on the locomotive, does use a higher pressure and/or a bigger 'hole' in the brake leaver, to fill the brake pipe, so it is a much faster process and filling it only using drive/release position. But you have to be careful to NOT overcharge the triple valves.
Quacking Duck Posted February 14 Author Posted February 14 Thank you for explaining what those buttons do. In what situation, and for what purpose, is the brake releaser intended to be used?
Agent B-7 Posted February 20 Posted February 20 On 2/14/2026 at 10:52 AM, Quacking Duck said: Thank you for explaining what those buttons do. In what situation, and for what purpose, is the brake releaser intended to be used? I use it to unlock the pneumatic traction lock on the locomotives that have it. Allows to apply the power while the rear of the train is still releasing the brakes, helps with hillstart etc (the brakes in the back will be eventually released and you already have some traction). Another thing is if you're switching and the brakes are in the T/G mode. If you intend to use only the local brake, you can keep it there and release the first time quickly with it. I know Americans use the independent brake bail to modulate the brake force or to use only dynamic brake on the loco itself, but it's definitely not intended use in Europe.
jeroezie Posted February 20 Posted February 20 12 minutes ago, Agent B-7 said: I use it to unlock the pneumatic traction lock on the locomotives that have it. Allows to apply the power while the rear of the train is still releasing the brakes, helps with hillstart etc (the brakes in the back will be eventually released and you already have some traction). Another thing is if you're switching and the brakes are in the T/G mode. If you intend to use only the local brake, you can keep it there and release the first time quickly with it. I know Americans use the independent brake bail to modulate the brake force or to use only dynamic brake on the loco itself, but it's definitely not intended use in Europe. One should not have the loco in G when shunting.... This is one of the first things they will ask if you have a accident/spad when you are shunting (or driving an P brake train).
Quacking Duck Posted February 21 Author Posted February 21 What are "T" and "G"? Does the "brake assimilation" button do exactly the same thing as the "fill" position on the brake lever? If no, what is the difference, and what is the significance of the difference?
Agent B-7 Posted February 22 Posted February 22 10 hours ago, Quacking Duck said: What are "T" and "G"? There are three main brake timing options (in Germany, Poland, Austria etc, but could be different otherwise): T or G (Towarowy/Güter, freight), P (in the past, passenger, now mostly fast freight), and R (rapid, fast passenger, but now basically any passenger). This determines how fast the brakes are released after pressurizing the main line on the locomotive and affected cars. The point is to delay the release on the front of the consist to make the release moment closer to the end of the consist, to make the brake release more uniform. 10 hours ago, Quacking Duck said: Does the "brake assimilation" button do exactly the same thing as the "fill" position on the brake lever? If no, what is the difference, and what is the significance of the difference? No, not sure if the Polish valves are any different, but in German context, the Fast Release (Fill) position is venting the main res to the brake line but doesn't intentionally overcharge over 5 bars, the relief valve is still active and will prevent excessive pressure. The point is to get the line to 5 bars ASAP. Brake overcharge/assimilation gets the pipe pressure above 5 bars (in Germany the typical limit is around 5.5), and the point is to not just release the brakes on the whole consist, but also fully charge auxiliary reservoirs on all the cars (that feed the brake cylinders on cars, they charge only when the brakes are fully released). 1
schmusegewürzkatze621 Posted Monday at 09:05 PM Posted Monday at 09:05 PM (edited) On 2/14/2026 at 2:52 PM, Quacking Duck said: Thank you for explaining what those buttons do. In what situation, and for what purpose, is the brake releaser intended to be used? Primarily when coupling or uncoupling a locomotive to/from a consist. It allows to keep the train braked while pushing the locomotive against the first wagon to compress the buffers so the coupler gets some slack in it. On 2/22/2026 at 3:45 AM, Agent B-7 said: There are three main brake timing options (in Germany, Poland, Austria etc, but could be different otherwise): T or G (Towarowy/Güter, freight), P (in the past, passenger, now mostly fast freight), and R (rapid, fast passenger, but now basically any passenger). This determines how fast the brakes are released after pressurizing the main line on the locomotive and affected cars. The point is to delay the release on the front of the consist to make the release moment closer to the end of the consist, to make the brake release more uniform. Yes and no. The difference between G and P is timing, that is correct; G brakes both apply and release much more slowly than P. But the timings on P and R are the same. Historically, with tread brakes (Klotzbremsen), R meant that the brake has a mechanism to switch to ‘high brake force’ (Hochabbremsung, hohe Abbremsung) above a certain speed (something around 60 km/h) which increases the brake cylinder pressure significantly to counteract the unfortunate property of tread brakes that the same brake cylinder pressure yields worse deceleration the faster the wheel is turning. Disc brakes, however, have a pretty constant deceleration over speed, so R disc brakes simply increase the pressure in the cylinder. R brakes also typically have wheelslide protection, while P brakes typically do not. On 2/22/2026 at 3:45 AM, Agent B-7 said: No, not sure if the Polish valves are any different, but in German context, the Fast Release (Fill) position is venting the main res to the brake line but doesn't intentionally overcharge over 5 bars, the relief valve is still active and will prevent excessive pressure. The point is to get the line to 5 bars ASAP. A German driver's brake valve does not generally protect against overcharging if you hold it in ‘fill’. But since you'd have to actively hold the handle pushed forward, it's not much of an issue, really. On 2/22/2026 at 3:45 AM, Agent B-7 said: Brake overcharge/assimilation gets the pipe pressure above 5 bars (in Germany the typical limit is around 5.5), and the point is to not just release the brakes on the whole consist, but also fully charge auxiliary reservoirs on all the cars (that feed the brake cylinders on cars, they charge only when the brakes are fully released). It depends on what kind of distributor you have. For old models like Kkg/Kkp/Kks, this may be true. In the KE, invented in the 50s and the most widespread design in Europe since then, the reservoir is recharged from the brake pipe if its pressure drops too low no matter if the brake is applied or released. The most important thing about brake assimilation not mentioned here is that the brake line pressure is raised and then lowered back to 5 bar very slowly, so that the brakes don't register it as brake application but their reference pressure still drops accordingly. With this, one can recover from slight overcharging, and in push-pull trains, this may also be needed after changing cabs, to account for inaccuracies in the 5 bar reference pressures of the different driver's brake valves and the slight drop in brake pipe pressure along the length of the train now going the opposite way. Edited Monday at 09:07 PM by schmusegewürzkatze621 1
Quacking Duck Posted 6 hours ago Author Posted 6 hours ago Much of what has been said in this thread appears to imply that the driver can choose between these brake timing settings. Is there some switch in the locomotive with which to do so? How do I know which setting is correct for a specific train? Similarly, in ETCS data entry, the driver has to choose between several brake timing options. How do I know which one accurately describes my train? I broadly understand that it is bad to overuse the "fill" position. What is the exact problem caused by doing so? How do I know when I have caused such a problem? Thank you for your patience as I try to understand Polish air brakes.
jeroezie Posted 3 hours ago Posted 3 hours ago Most vehicles come with a valve to sett the G, P or R (or whatever fancy a passenger vehicle comes with, or it may only have normal R for a simple passenger vehicle). Some trains do have it in a computer screen, such as the Dragon 2. It used to be, that you could not set it in the Dragen2 but you can actually change it nowadays. But what to set it to? That is complicated since the trains do not come with a proper brake information sheet or timetable. But in MP, it should spawn in set currently up. In SP the scenario maker should somehow provide the info. But even the SimRail made scenario's do not always have it. But you can figure it out! When shunting, use never G but always P or R (R setting does not do anything useful at low speed, so P and R are kinda the same when shunting). When driving a train, you can use dev menu to look up to what brake setting the wagons are set, press the (default) key bind F8, then open player trainset. After the vehicle number the will be in [ ] the brake setting. If all vehicles have G, use G. If the first 5 wagon units have G and the rest have P, use G. If its all P, you can use P. If all has R, use R if possible, otherwise P. This does only not account for the case where the loco should run in G but all wagons in P, but you wont derail if you sett the loco illegally in P. In Dragon2, use TDD 2, then the G or P under Tryb ham.: to set the triple valve setting (G or P).
jeroezie Posted 3 hours ago Posted 3 hours ago (edited) This is what it looks like on a cargo wagon. The small pull thiny on the far right is the air drain, when you need to purge the air from an wagon. In the middle, the red valve pointing straight down, the triple valve isolation valve (for isolating the brakes, if defective, do not forget to purge the air after isolating it). The yellow valve with round know is the GP changeover valve, here with Polish T and O inscriptions (The French like to use M and V). On the left, the square empty/loaded changeover leaver, for altering the brake force when running empty (or partially loaded) or almost fully leaded. The yellow text on the main beam is the brake inscription, O-GP SAB DRV2A-450. Edit: I just noticed the numerals on the empty/load changeover leaver are wrong, how fun. Edited 3 hours ago by jeroezie
jeroezie Posted 3 hours ago Posted 3 hours ago A picture from the other side of the same wagon. Notice the || design of the triple valve isolation valve, this is on purpose, for easy recognition among all rolling stuck, even if a unknown wagons is suddenly in your train, that normally runs on the other end of the continent. Most locomotoives use a very similar design too. The round design of the know of the GP valve is good too see here too, as is the square design of the empty/loaded lever (here with more sensible numbers).
schmusegewürzkatze621 Posted 13 minutes ago Posted 13 minutes ago 5 hours ago, Quacking Duck said: Much of what has been said in this thread appears to imply that the driver can choose between these brake timing settings. Is there some switch in the locomotive with which to do so? How do I know which setting is correct for a specific train? It's the job of whoever puts the consist together to apply the various rules and regulations of which brake settings to use where and when. As a driver driving a ‘finished’ train you normally don't have to worry about that. 5 hours ago, Quacking Duck said: I broadly understand that it is bad to overuse the "fill" position. What is the exact problem caused by doing so? How do I know when I have caused such a problem? If the pressure in the reference reservoir (A-Kammer) in the distributor gets too high – say, 5.5 bar – and the brake pipe pressure drops back to 5 bar too quickly, the distributor will apply the brake. (After all, 5.5 bar reference and 5 bar brake pipe is indistinguishable from 5 bar reference and 4.5 bar brake pipe.) And then you will be accelerating, thinking the brakes are released, but actually they're applied and running hot. Or, alternatively, you won't be able to get the train moving at all. If this happens and the difference in pressure is not too great, brake assimilation will fix it. If not, then the only thing you can do is pull that handle you see in the post above to ‘purge the air’ as jeroezie called it. On an ancient single-release triple valve, this would empty out the one and only reservoir that supplied both reference pressure and air for the cylinder. On a modern (KE or similar) distributor, this empties out the reference reservoir without touching the one that supplies the cylinder. 5 hours ago, Quacking Duck said: Thank you for your patience as I try to understand Polish air brakes. It's UIC/European air brakes in general. They all work pretty much the same.
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