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Proper Train Handling For North American Diesels

Discussion in 'PC Discussion' started by JustWentSouth, Mar 3, 2021.

  1. JustWentSouth

    JustWentSouth Well-Known Member

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    I have seen this topic come up in several threads and thought I would try to consolidate things with a thread here.

    I will start off by referencing an excellent video by anthony.wood of Searchlight Simulations about proper train handling with the CP AC4400 in TS:



    From this, I infer that you should bail off the independent brake quickly after a set on the train brake. Indeed, the brake cylinder light flashes in this loco until the independent brake is bailed. I also infer that it is OK to place a set on the air brakes and ride it for a while. What loses the air are multiple sets and releases.

    So, for balanced braking, I either start off with the dynamic or an air set depending on the grade and, if the dynamics alone can't hold the train, try to wind up with a blend of air and dynamics that maintain a steady speed.

    However, I have no direct experience in the cab, so I could be wrong!

    For those like me who are always seeking a better understanding of the vagaries of the triple valve, I find that this diagram from a 2018 Trains Magazine article quite helpful in understanding how you can lose air going downgrade with multiple sets and releases if you don't allow the brake cylinder to recharge between sets.

    IMG_5223.jpeg
     
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  2. solicitr

    solicitr Well-Known Member

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    That pfft-pfft-pfft sound you often hear shortly after releasing the train brake is the air compressor re-filling the main reservoir (it kicks in below ~130 psi). As long as your brake cycles allow time for that to happen, you won't run out of air.

    The issue with riding the train brake down the grade isn't air, but overheating the brake shoes, which can cause them to fail (IDK if the game models this).

    The point of baling off is to reduce the amount of jostling caused by bunching: if you don't bale off, then when you release the train brake a quarter-mile's worth of cars will ram into the back of the loco, making for a very jerky ride. Baling off releases the loco brake, only, letting the loco run out the coupler slack. Baling off too soon while the train brake is applying (remember, it can take a long time for the pressure change to propagate down the length of the pipe) can cause the opposite, equally unpleasant: the loco being jerked up short as the wagons slow down behind it.
     
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  3. Crosstie

    Crosstie Well-Known Member

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    Interesting. I find it much more difficult to maintain a consistent downgrade speed when using the dynamic brake on the AC4400CW than with the older locos. I end up riding the auto brake more than I like (mostly in minimum application). I also find the dynamic brake to be inconsistent at braking, so I find myself moving it up and down the notches more than I think a real driver would.
     
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  4. stujoy

    stujoy Well-Known Member

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    That’s because it doesn’t work as it should in TSW2. Instead of a fairly consistent braking force typical of AC locos, the dynamic braking increases as your speed drops, meaning you then reduce your input. Then as the train speeds up, the dynamic brake force decreases and you have to apply more. This will repeat forever as the braking force will never stabilise. DTG are aware of the issue and a fix was on the roadmap In Planning section until the reformatting of the roadmap.

    The dynamic brakes on the other (DC) locos work correctly and the braking force will increase as the train gets faster, and once you have near enough the right input, will stabilise naturally until the gradient changes. That makes it possible to control the speed properly, with or without a bit of air brake. Impossible to achieve currently with the AC4400.
     
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  5. Crosstie

    Crosstie Well-Known Member

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    You're quite right. Good to know that someone's keeping track of this sort of thing. I guess this particular fix may have ended up in the circular file. Coincidentally, the upcoming Cane Creek route has the same locomotive. It will be interesting to see if the dynamic brake on this one works correctly, although I'm not sure of the grade profile on that route.
     
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  6. Matto140

    Matto140 Well-Known Member

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    As far as I know, max. gradient on Cane Creek is about 1.2% but on significantly shorter distance.
     
  7. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    With Westinghouse triple valve based brakes, once you equalise the air pressure in the car/wagon reservoir and the brake cylinder you cannot apply more brake force. This is what people usually refer to when they say "run out of air". This happens if you apply, and release then apply again repeatedly before your train brake pipe has charged all the reservoirs back up throughout the entire train. For a monster long freight this can take many minutes to recharge. For the trains I play with it takes about a minute. When you're getting close we're trained to use whats left to stop then, apply the loco brake and release and recharge the entire train and not move again until the guard confirms the rear of the train has come back up to full pressure. This old BNSF training video is a good set of information on triple valve based Westinghouse brakes.

    Paul
     
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  8. solicitr

    solicitr Well-Known Member

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    Which is why with a long consist, you need to monitor the EOTD brake pressure. Again, the way to proceed is to brake significantly enough to reduce speed by an appreciable amount, so that you won't have to brake again until the system has recharged.

    --------------------------

    By "riding the brakes" I mean setting some combination of train and loco brakes that maintains speed on the downgrade and leaving them there indefinitely. The game lets you get away with this, but in RL you'd be courting brake failure due to overheat.
     
    Last edited: Mar 6, 2021
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  9. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    In real life you'd melt your cast iron brake blocks on your steel wheels :)
     
  10. Monder

    Monder Well-Known Member

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    How long would the brakes probably last before this happening IRL?
     
  11. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    I suspect it would greatly vary depending on how steep the grade was, how good the brake blocks where and a million other factors. That is a useless answer I know, if you consider the San Bernadino train disaster sometime partway down from Cajon Pass the train overcame its dynamic brakes and the engineer attempted an emergency application of the air brake - this could not stop the train but probably did slow it down, for a while until friction simply wasn't enough - I would *guess* about that point the brake blocks had a layer of liquid metal. You can read about it at https://en.wikipedia.org/wiki/San_Bernardino_train_disaster

    I would love to give you a link to an authoritative source and while I found one it appears the NTSB website is down https://www.ntsb.gov/investigations/AccidentReports/Reports/RAR9002.pdf
     
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  12. Nozomi329

    Nozomi329 New Member

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    I just looked at this report and found that SP have maximum brake pipe reduction limits as well as speed limits for different train weight-brake force ratios. Wonder if the railroads today still have these limits?
     
  13. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    Yes they very much do. Even the heritage railway that I volunteer on has weight limits that are based on the locomotive(s) and section of track. These limits are both for the ability of the locomotive to lift the train up the steepest gradient in the section, but also the train's ability to safely descent the same gradient which is based both on the physical braking limitations but also on the locomotive's ability to recharge the brake line and reservoirs after an application.

    Paul
     
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  14. raretrack

    raretrack Active Member

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  15. solicitr

    solicitr Well-Known Member

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    What genius at the FRA thought it was a good idea to require that emergency brake application disabled dynamic braking?
     
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  16. cwf.green

    cwf.green Well-Known Member

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    As far as I know, you should bail off the independent brakes at the same time as you apply the train brake (i.e you never want the brake cylinder pressure to go above zero, unless you are below 10 mph). The way it is modelled in the TS2021 AC4400 you sometimes need to press the bail-off button twice or wait until after a brake pipe reduction to press it, so I'm not sure that the brake cylinder pressure gauge in TS2021 should be relied on to prescribe how you would handle the train irl.

    On the AC4400 (and many other NA diesel electric locomotives) the independent brakes are incredibly strong (they can hold a heavy train in relatively significant grades, after all) so you run the risk of making the locomotives slide, or overheat, if you don't bail off the independent brakes.
    Also, as someone mentioned, the strong brake force of the independents will very likely cause a run-in (train bunches up "violently") unless bailed off, which is bad.
     
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  17. solicitr

    solicitr Well-Known Member

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    That makes sense, but I wonder how that works in real life, as a physical matter, with a traditional control stand? You couldn't do it with one hand, and you couldn't use your right without turning and taking your eyes off the track.
     
  18. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    You would be surprised how rarely a driver looks at the track. They glance a few hundred metres ahead then head down with the controls when they're doing busy things like managing a train down a hill.

    Paul
     
  19. Monder

    Monder Well-Known Member

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    And this is just me guessing, but I think a skilled engineer knows the controls well enough, so they don't need to look at them all the time. You don't look at pedals and gearstick in a car all the time.
     
  20. solicitr

    solicitr Well-Known Member

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    It's not needing to look at them, but the need to use both hands on levers located to the left of and slightly behind the driver. You simply can't reach them with your right without turning around. I never look at the pedals in my car- but I do have both feet available!

    Besides, with the controller valve set to freight mode, the application of the loco's brakes is retarded to occur later than the cars' application, which ought to give plenty of time to bail off after setting the train brake.
     
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  21. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    Your hands and feet do tend to learn the locations and feel of the controls but you are watching your gauges and controls constantly, much more than you look out the window. You're also listening for tell-tale sounds and vibrations. Most locomotives have plenty to look at. They're not like cars, you're in control of a beast in a big diesel pre computer control. This is likely less true for the modern computer controlled diesels. The controls are also very picky - moving 2mm can be enough to cause a brake application for example. Every locomotive is also subtly (and sometimes very) different. On a real railway you're not likely to have the same one every day or even the same type every day unless you're trapped in passenger electric.

    Paul
     
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