Dodgy physics

[arizonachris]

Funny, in RW I never see the brake pressure over 90psi. These tunnel motors are still baffling me, the brakes are so bad. It must have been the goat that programmed them.

[Rich_S]

Funny, in RW I never see the brake pressure over 90psi. These tunnel motors are still baffling me, the brakes are so bad. It must have been the goat that programmed them.

Hi Chris,
Brake pipe should be 90 PSI when the brake pipe is fully charged. The main reservoirs should be at 140 PSI when they are fully charged. I'm not sure where RSC is getting their brake information from? As for the movement of the Automatic brake handle, well I've been setting mine to the values available in RW_Tools.

Regards,
Rich S.

[Kali]

Hi Kali,
Here's another one for you. If you shut the engine down via the "Z" key and just coast down the track, somehow the air tanks magically get recharged as you use air? This is very funny since most EMD's have shaft driven compressor's and most GE's have 3 phase compressors. In both cases if the diesel engine is not running, you don't have an air compressor to recharge the tanks One last note, on most modern locomotives the compressor shuts off at 140 PSI and kicks on at 130 PSI, but you'll find cases were you might drop down to 125 PSI before the compressor kicks on. It usually take several quick applications and releases of the independent brake to drop the pressure from 140 PSI to 130 PSI.

Well they got the reservoir pressures right :) I'm going to have to script the whole lot, so I can make the compressors dependent on RPM. Someone's going to have to give me ideas about recharge times in different power notches.

And yes, the independent brakes do seem to work backwards in RW. When apply the brakes there is no drop in main reservoir air pressure, but when you release the independent brake then the main reservoir pressure drops and instantly recharges? The main reservoir pressure should drop as you apply the brakes. Another thing I've noticed is RW seems to treat a independent brake application like a Automatic brake application which is totally incorrect. The independent brake sends air directly to the brake cylinders on the locomotive, so there should not be any delay like you get with a Automatic brake application. I know this is a problem Kuju had before trying to make one size fit all, but in doing so we end up with braking systems that are not working correctly

Regards,
Rich S.

The "instant recharge" is because the compressor is as overpowered by default as the dynamic brakes are - if you go and edit "compressor power" - it's something like that - and move the decimal point two digits to the left, then suddenly it takes half a minute to recharge one PSI. That was why I was asking about how big the reservoirs are, because by default 5-6 applications of the independent brake pretty much kill the reservoir. Given the size of a locomotive brake cylinder I can't imagine you'd even see the needle move much, let alone losing 10% of the reservoir...

The brake delay for the straight-air brake can be got rid of easily - it was pretty annoyingly long by default on the SW1500s. Thankfully it's a seperate brake system.

[Rich_S]

Someone's going to have to give me ideas about recharge times in different power notches.

Hi Kali,
The only thing I can tell you is the GE Air Compressor has a constant output regardless of throttle setting, because it's driven by a 3 phase A/C motor. The EMD's are different because they are shaft driven off the diesel engine so their output does increase up to about notch 4. If I remember correctly beyond notch 4 and you are just spinning the compressor faster but not really increasing it's output.

Regards,
Rich S.

[arizonachris]

You're right, Rich, I'm looking at brake pipe pressure, not resevoir.

[Kali]

Maybe I should ask this in a different way;

You've made a pretty heavy application to stop so you've got 70psi in the train pipe, 140 in the main reservoir, and now you want to get going again. Ok, so you release, the train pipe starts climbing slowly and all the brake cyls discharge, and off you go. Lets say you have 3 head units and 80 cars ( just because that's what every other question has had ), how much can you expect the train pipe pressure to have raised by the time the main reservoir pressure falls to meet it? I'm not looking for absolute numbers here, just rough ideas... maybe if you've got full reservoir tanks the MR pressure won't even drop to pipe pressure with one release/recharge, I don't know.

One thing I don't want to do is code something that leaves people sitting around for half an hour while a system recharges - I can do that as an option obviously, but most people don't want to stare at a game doing nothing when they fire it up.

[Rich_S]

Maybe I should ask this in a different way;

You've made a pretty heavy application to stop so you've got 70psi in the train pipe, 140 in the main reservoir, and now you want to get going again. Ok, so you release, the train pipe starts climbing slowly and all the brake cyls discharge, and off you go. Lets say you have 3 head units and 80 cars ( just because that's what every other question has had ), how much can you expect the train pipe pressure to have raised by the time the main reservoir pressure falls to meet it? I'm not looking for absolute numbers here, just rough ideas... maybe if you've got full reservoir tanks the MR pressure won't even drop to pipe pressure with one release/recharge, I don't know.

One thing I don't want to do is code something that leaves people sitting around for half an hour while a system recharges - I can do that as an option obviously, but most people don't want to stare at a game doing nothing when they fire it up.

Hi Kali,
This is where you start getting into the one size does not fit all category If you've dropped the brake pipe pressure by 20 lbs, you've put 50 lbs into the brake cylinders on each car. So now you not only have to raise the brake pipe pressure by 20 lbs, but you also need to replenish the 50 lbs for each cars main reservoir. So let's just say we use the values of the Wabtec 3CD compressor, the compressor output at 1000 RPM is 307 CFM or 8694.24 liters/min and 140 PSI max (which I wonder about as well, because the compressors have a 150 lbs pop-off). This is the part where I ask how many cubic feet of air are in a 90 PSI tank? But like you mentioned earlier, you also don't want people to wait 15 minutes to pump up the brake pipe either, so hopefully there is a happy medium in here somewhere?

Regards,
Rich S.

[Kali]

The advantage your system has over ours is you can drive off while you're still bringing the train pipe back up to pressure. ( the advantage of ours is of course the main reservoir is the entire length of the train so it doesn't matter ). But generally are you expecting one release/recharge cycle to empty the main reservoirs - at least to the pipe pressure? I have no idea how big the reservoirs are. I have actually been wondering how much volume there is in the air system in an average freight car, it's not the easiest thing in the world to dig up because who usually wants to know that stuff.

Ugh, vacuum brakes were so easy. Brake cylinder and reservoir all in the same device, and impossible ( well, improbable ) to run out of vacuum. You have to charge the entire system to get the brakes *off*.

[Rich_S]

The advantage your system has over ours is you can drive off while you're still bringing the train pipe back up to pressure.

Actually you should not because you have a great chance of dragging empty cars causing flat spots. This is also something that happens during a heavy brake application, a empty car may slide it's wheels while the loaded cars are slowing the train, but I'm getting off topic

But generally are you expecting one release/recharge cycle to empty the main reservoirs - at least to the pipe pressure? I have no idea how big the reservoirs are. I have actually been wondering how much volume there is in the air system in an average freight car, it's not the easiest thing in the world to dig up because who usually wants to know that stuff.

No, Yes, not really, ummmm. Actually this has to do more with air compressor volume than anything else When you move the brake handle from lets say a full application back to release, the compress will begin charging the brake pipe and the brake pipe will begin charging the air tanks on each car. This is a continuous action, not a stop and start action, so you don't see the air pressure rise and fall. Think of filling your bath tub with water, you don't keep turning the water on and off, you leave the water on until the tub is full. Think of your bath tub as the brake pipe. Now that the tub is full of water (i.e. all of the cars air tanks are full and the brake pipe pressure is at 90 lbs) you want to make a brake application so you drain some water out of your tub, lets say 10 PSI worth. At this point the compressor does nothing, and now the brake pipe went from 90 PSI to 80 PSI and the air tanks on each freight car sent 25 PSI to the brake cylinders. As long as you don't move the brake handle nothing else will happen. Ok now the train has stopped so you move the brake handle to the release position. Now your tub is low on water, that is the system knows you should have 90 PSI in the brake pipe at release not 80, so the air compressor turn on (you open the faucet and begin refilling your tub) as the compressor puts air back into the brake pipe the triple valve on each freight car sees the brake pipe pressure is greater than the air tank pressure and does two things. 1) it starts to vent the air in the brake cylinders to the atmosphere and secondly it uses the air in the brake pipe to recharge the air tanks on each car. What you see in the cab is the Brake Pipe and Equalizing Reservoir pressure begin to increase. The last piece of the puzzle, you will see the main reservoir pressure drop when you move the handle to release to lets say 110 PSI, but because of the output of the compressors you will not see the needle rise and fall, it will be a steady climb (slow but steady depending on the length of the train) until the complete system is recharged. So long story short, you never empty the main reservoirs unless there is a drastic problem, but yes you could see the MR drop down to 120 PSI when you move the automatic brake handle to release, the compressor will kick on as soon as the pressure drops to 130 PSI and begin supplying air to the MR which supplies air to the Automatic brake value, which supplies air to the brake pipe, which finally supplies air to the freight car air tanks. I hope this makes some sense?

Regards,
Rich S.

[GaryG]

NitPick - The air tank supplies air to the brake stand/trainline and the compressor supplies air to the air tank(s) of the loco.

All the connected locos do have one MU hose connecting all the loco air tanks together. See http://www.railway-technical.com/us-musp.shtml

Not that it really impacts this discussion too much but it does effectively mean a larger main air tank is available with multiple compressors.

GaryG

[Kali]

The last piece of the puzzle, you will see the main reservoir pressure drop when you move the handle to release to lets say 110 PSI, but because of the output of the compressors you will not see the needle rise and fall, it will be a steady climb (slow but steady depending on the length of the train) until the complete system is recharged. So long story short, you never empty the main reservoirs unless there is a drastic problem, but yes you could see the MR drop down to 120 PSI when you move the automatic brake handle to release, the compressor will kick on as soon as the pressure drops to 130 PSI and begin supplying air to the MR which supplies air to the Automatic brake value, which supplies air to the brake pipe, which finally supplies air to the freight car air tanks. I hope this makes some sense?

Regards,
Rich S.

That was what I was after - I wasn't sure if recharging the system was faster than the compressors or not, if it wasn't then the MR would slowly empty to the level of the train pipe until that was fully charged and stable.

RE: empty/loaded issues, do they not auto adjust for weight? ok that isn't foolproof :). What's the issue with them not releasing with the others though? not anything I can simulate, but one of those nice-to-know quirks.

[tbundy1982]

RE: empty/loaded issues, do they not auto adjust for weight? ok that isn't foolproof :). What's the issue with them not releasing with the others though? not anything I can simulate, but one of those nice-to-know quirks.

Auto adjust for weight? There are some North American freight cars that have a load sensing device. From what I remember, tankcars that I used to deal with for ethanol loading had load sensors that would sense the compression of the truck springs by judging how close the truck frame was to the car frame, or, specifically, the bolster of the car at the "B" end. Also, from my experience, most all of these load sensors were not being used, perhaps being manually cocked up and away from the truck frames. I think I have seen this kind of device on newer coal gons as well. Few, if any, were used on covered hoppers that I remember. Sadly, my experience is limited by the car types that the railroad handled where I worked. Working on a shortline in the midwest, it was primarily covered hoppers and tankcars. Maybe this can be expanded upon by more experienced individuals.

I'm not entirely sure what you meant by some not releasing with others.

This may have been mentioned in a previous post, but when the automatic brake is released, standard US freight cars go into a "full release" mode that is triggered by air pressure change. Once the air pressure begins to rise in the brake pipe, each car's triple valve senses that change and it takes only a small amount of change to send the car into "release" mode. Too small of a change, and the brakes will not release at all. An example might be making an application, accidentally releasing it, and then moving the application handle back to it's applied position, all within a few seconds. I would think that this would be frowned upon because of the odd consequences it could have with sticking brakes or some cars being released with others applied. An additional example would require the controlling locomotive to have a non-self-lapping brake, like a 6 or 24 brake that could allow the engineer to make a reduction of only 2-4 PSI. That could certainly cause some of the problems described above as well. An experienced engineer could probably elaborate on this subject more.

I wish I knew more about this subject, or at least a better way of communicating the knowledge I do have. I was never an engineer, but learned much as a conductor about brakes and how trains worked.

Thanks you all of you for putting in the time and thought to try to make this a better game. I too was disappointed with the game physics but I'm reading and tinkering as well.
Tyler

[Kali]

I'm not entirely sure what you meant by some not releasing with others.

It was in response to RichS's comments about not driving off until everything's recharged because you might end up dragging a car or two with it's brakes on. I think, anyway! that was some time ago. I don't quite get that, for the very reasons you've said - IE enough increase in trainpipe pressure will trigger a release. I guess if one of the sensing mechanisms is sub-optimal then you wouldn't get a release without bringing the pipe right up to 90?

[Rich_S]

It was in response to RichS's comments about not driving off until everything's recharged because you might end up dragging a car or two with it's brakes on. I think, anyway! that was some time ago. I don't quite get that, for the very reasons you've said - IE enough increase in trainpipe pressure will trigger a release. I guess if one of the sensing mechanisms is sub-optimal then you wouldn't get a release without bringing the pipe right up to 90?

Hi Kali,
There are so many different variables when referring to brake systems, one size does not fit all, but if we were talking about ideal conditions on a 100 car freight train with each car being 50 feet in length and zero brake pipe leakage. It takes about 2 lbs of increase in brake pipe pressure to trigger a release. It also takes about 12 seconds for the last car in the train to begin to see the brake pipe increasing, at this point the very first car already has it's brakes released. The next variable is how much of a reduction did you take? Not only do you have to raise the brake pipe pressure but you also have to recharge the air tanks on each car. So again in ideal conditions making less than a full service application it may take 2 minutes to completely recharge the brake pipe. So my point was, just because you moved the handle to release does not mean your ready to open the throttle, sure within 20 seconds all of your brakes on the ideal 100 car freight train are probably released, but do you really want to start off down the track without having all of the air tanks fully recharged and the brake pipe still below 90 lbs. What gets tough is when you start thinking about mixing different cars lengths in your train, the longer the brake pipe the slower the response time. One last thing to go along with this, Rail Works does not handle engine loading properly. Unless you've received a penalty application, the engine will load regardless of brake pipe pressure. Yes you can load the engine with the independent brakes fully applied and the automatic brake in full service. If you do something bad may happen, but you can do it. For some unknown reason Rail Works will not allow the engine to load if brakes are applied? So there is still more work to do, but hopefully we will get there someday?

Regards,
Rich S.

[Kali]

UK locomotives cut the power over a certain brakepipe pressure, I assume that's why it's that way.