Brake System Questions

Discussion in 'TSW General Discussion' started by voltajtepes#7278, Feb 14, 2021.

  1. voltajtepes#7278

    voltajtepes#7278 Member

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    Ok I'm doing some reading to better understand how the air brakes actually function, and the purpose of the gauges and auto-brake positions.
    Just a few questions.
    I've found diagrams showing Main Reservoir (I assume in the loco), Aux Reservoir (I assume in each car), Brake Cylinder (in each car).. I understand those three and the basic theory. I found those three gauges and I think I understand what they represent. I found some good diagrams with the air flow showing for the different cases.
    However, I'm confused on a few things:
    There is a fourth gauge labeled "EQ-LG" Reservoir
    I don't see this in the diagrams that I have found. Where is this located? Is it on the loco or does each car have one?
    The positions of the auto-brake. Is there a position on the North American train auto brakes that corresponds to the "Lapped" position? OR is there a description specifically dealing with the North American trains?
    So far I think I have the theory .. sort of down lol...
    Any links or websites are greatly appreciated!
     
    Last edited: Feb 14, 2021
  2. solicitr

    solicitr Well-Known Member

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    Air brake systems can be either manually lapped (as seen in the Class 66 and the F40PH) or self-lapping (the CSX locos). The latter system (known in the US as "26L") allows you simply to set a given brake force according to the position of the brake handle, not unlike an automobile's brake pedal. Self-lapping brakes can also be "feathered," in other words the brake force can be reduced without fully releasing. Manual lapping ("24RL" in US parlance, as well as the obsolete Type 6) is apparently the system you've been studying, where the driver has to set the handle to "lap" when the brake cylinder pressure reaches the desired level.
     
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  3. voltajtepes#7278

    voltajtepes#7278 Member

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    Ok this is all making sense. And in the loco I now understand the four gauges. The only confusing thing left for me is if each car has a brake cylinder, why is there only ONE brake cylinder pressure gauge. Same goes for the Aux reservior.
     
  4. solicitr

    solicitr Well-Known Member

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    Well the dash would get pretty crowded if there was a dial for every car in a 100-car coal train!
     
  5. Olaf the Snowman

    Olaf the Snowman Well-Known Member

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    So if you had a 12 coach train (e.g. Class 395), you would like to see 12 brake cylinder gauges in the cab? :o
    Not only would it be a mess and an overload of information, it’s completely unnecessary. The brake cylinder gauge in the cab shows the brake cylinder pressure for the leading vehicle/locomotive. You can assume all the other vehicles have the same braking effort*- I use the phrase braking effort not brake cylinder pressure because the brake control computers will automatically determine how much brake cylinder pressure is needed depending on how much dynamic braking effort is available. So on another vehicle, you may not necessarily get the same brake cylinder pressure as your vehicle/loco but braking effort will be the same. If you’re talking about loco-hauled stock, then it’s even simpler because there is no dynamic braking on vehicles and no computer to determine how much brake cylinder pressure is needed.

    *Unless you’re using independent brake

    It’s the same reason why you don’t have multiple ammeter gauges. On a HST, there are 4 traction motors per power car yet you only have one ammeter gauge. Of course, on modern units, you don’t even have an ammeter gauge. It’s unnecessary information and would clutter the desk.


    Main reservoir runs throughout the train. So you’ll have main reservoir connected between locomotive and coaches. You’ll also have brake pipe and if you’re a passenger train, ETS cable too.


    Equalising reservoir: In very simple terms when you make a brake application, you’re actually effecting the equalising reservoir. The brake pipe then mimics what you do to the equalising reservoir. The reason being is if you controlled the brake pipe directly, the brake pipe is extremely long which means it will be hard for the driver to know how much brakes are being applied. Only once the brake pipe has stabilised would you get a reliable reading. So they designed a small reservoir called the equalising reservoir to overcome the above.
     
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  6. breblimator

    breblimator Guest

    Brake Cylinder (BC) - loco brake pressure // 0 PSI = released
    Main Reservoir (MR) - total air 'to disposal'
    Equalizing Reservoir (ER) - target air pressure for Brake Pipe
    Brake Pipe
    (BP) - whole train brake pressure // 90 PSI = fully released

    read-me

    PS For US trains - definition of released brakes:

    Air Flow <60 (AFM indicator)
    Rear >75 PSI (ETD/EOT)

    UPDATE The engine in the locomotive is such a generator that runs on fuel. Produces electricity that drives the traction motors and a compressor (you can hear it turn on sometimes). When the train brakes, air escapes from BP - it is irretrievably lost. When you try to unbrake the train again (to increase PSI), you use an MR air. The compressor replenishes the deficiencies in MR, de-facto pumping BP. A big simplification. BR
     
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  7. voltajtepes#7278

    voltajtepes#7278 Member

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    Excellent! Thanks to all of you! I would be ok with 500 gauges lol.. that way I know how each car is going :) I'm a numbers/data freak.
    Don't know where I would fit those, however .. maybe I would have a secondary car that contained just gauges.
     
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  8. breblimator

    breblimator Guest

    Oh, really? Then here is the version for you, fully official :D
    source
     

    Attached Files:

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  9. Olaf the Snowman

    Olaf the Snowman Well-Known Member

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    If the system wasn’t fail safe, I would agree. You would need to manually check each gauge to ensure you’re getting correct braking force for each vehicle. But the system is fail-safe. So you can be sure the brakes will work. If there’s any air leak, this would cause emergency brakes to apply because the system needs air in order to hold off the brakes. Vacuum brake is the same principle- a lack of atmospheric pressure is needed to release the brakes. As well as modern units with electropneumatic brakes are also fail safe because anything that causes the train wires to be de-energised will result in an emergency brake application. Even the parking brake system is fail-safe because modern parking brakes require air to hold off the spring to release parking brake. If there is an air leak in the parking brake system, the parking brake will apply.

    At least in the UK, all drivers across the network must perform a running brake test at the first available opportunity in their journey which will also prove that brakes are functioning as elected. On loco-hauled stock, a brake continuity test is done to ensure the continuity of the brake pipe.
     
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  10. voltajtepes#7278

    voltajtepes#7278 Member

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    That makes sense. They could put pressure sensors in each cylinder and have a main reading then a click through thing where you could select any car... but yeah I get your point.
    Learning all this made me realize thing that I never knew and that now scares me. I always thought air brakes on a train meant that if you lose air pressure your brakes are forced on using a spring, such that if you had no air the brake was on. This made sense to me. So the air just pulls the piston away to release the brake. Boy was I wrong!.
    This means you CAN run out of air if something bad happened and have a run-away train. I understand that there are probably safety functions built in nowadays but even so, that's interesting to me.
     
  11. breblimator

    breblimator Guest

    that way :)
    WIKI for more data
     
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  12. solicitr

    solicitr Well-Known Member

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    Except that, if the BP ever loses pressure, the air in the AR (+ the emergency reservoir) will slam the pistons hard over and lock the brakes. In fact, that's how emergency braking works- it vents the brake pipe to atmosphere. (The same mechanism also keeps cars from moving when uncoupled, because their brake pipes vent as soon as disconnected)
     
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  13. breblimator

    breblimator Guest

    A good example of BP integrity compromised :D
    PS coupler physics is missing in TSW - maybe someday \o/
     
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  14. Olaf the Snowman

    Olaf the Snowman Well-Known Member

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    With regards to running out of air, this is the exact reason why you have a parking brake. You use the parking brake when the wagon/loco is going to held for a long period of time. And on modern units, the parking brake is automatic. So when Main reservoir drops below 5 bar, the parking brake will automatically apply- as said previously, this system is fail safe because it requires air (main reservoir > 5 bar) to overcome the spring which applies parking brake. For normal train brake on modern trains, main reservoir needs to be above 7ish bar before the train wires are energised and thus brake release can be obtained.

    No, in simple terms you’re actually correct. There’s two parts to the air brake which I think you’re getting confused about. First is the brake pipe which will decrease in pressure when brakes are applied. And then the second is the auxiliary reservoir which will feed the brake cylinder. Even electropneumatic brakes (on modern trains) still use air for the brake cylinder albeit the method to communicate to the brake cylinder is done electrically (train wires instead of brake pipe).

    To complicate matters, it’s actually the auxiliary reservoir which feeds the brake cylinder. So saying that a reduction in brake pipe will cause a brake application is not strictly correct in the triple valve system. Because if you’ve just applied the brakes and then released them and then suddenly reapplied them again, you’ll get a brake pipe reduction but you won’t get brakes applying. This is because whilst the brake pipe may have recharged to 90psi, the auxiliary reservoir hasn’t recharged. So what causes a brake application is the concentration gradient between brake pipe and auxiliary reservoir- when aux reservoir > brake pipe, this will cause brakes to apply. But if you’ve suddenly applied, released and applied again, you won’t have that concentration gradient because aux reservoir hasn’t recharged or if you do have a concentration gradient, you won’t get as much as you would expect. This is what drivers mean when they say they've ''run out of air.'' They still have emergency braking available but obviously not ideal.

    The above reason is also one of the three main reasons why brake pipe in passenger trains is higher than in freight (110 psi vs 90 psi). As you have 110 psi in passenger, you're less likely to run out of air as opposed to if brake pipe is only charged to 90psi.

    First application:

    Brake pipe: 90 psi -> 80 psi
    Aux reservoir: 90 psi -> 80 psi
    Brake cylinder: 0 -> 25 psi

    You've released:

    Brake pipe: 80 psi -> 90 psi
    Aux reservoir: 80 psi -> 85 psi
    Brake cylinder: 25 psi -> 0 psi

    You've reapplied before aux reservoir has fully recharged:

    Brake pipe: 90 psi -> 80 psi
    Aux reservoir: 85 psi -> 80 psi
    Brake cylinder: 0 -> 12.5 psi when you would have expected 25 psi
     
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  15. mldaureol2

    mldaureol2 Well-Known Member

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    Hence the saying “if it won’t blow, it won’t go”
    Mike
     
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  16. voltajtepes#7278

    voltajtepes#7278 Member

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    Thanks again for the responses. It is very clear to me now. I found a few diagrams on the internet and I can follow your sequence with these.
    Very cool stuff!
     
  17. voltajtepes#7278

    voltajtepes#7278 Member

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    Wow that video!!! COOL!
     
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  18. solicitr

    solicitr Well-Known Member

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    I think its cool that you can actually see the cars venting, since in the cold air vapor is condensing and you get little white jets from each car.
     
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  19. geloxo

    geloxo Well-Known Member

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    In order to command brakes on the wagons you have a total air pressure measured by the main reservoir. You set brake effort on each wagon cylinder by changing the pressure on the whole train line (the brake pipe). As air flow starts in the leading locomotive that indication is the one given in the brake gauges, expecting it to be replicated on each wagon afterwards via the brake pipe. The equalizing reservoir is the one that helps you to set a brake pipe new pressure (braking effort target) which is the other indication in the gauges.

    If you use too much air by applying and releasing brakes too frequently the available air will be depleted before compressor can create more and you may lose your braking capabilities because the brake pipe pressure is too low and therefore the difference between the current pipe pressure and brake cylinders is going to be too small as well, so you could command less effort to the cylinders each time unless new air is generated to fill the brake pipe. This is mainly a problem on very long trains as in the the shorter ones compressor usually can work efficiently to generate new air even if you apply and release them very quickly, as the pipe is shorter and therefore less air is needed.

    This braking constraint is simulated in game. For instance is the following case I will only reach around 20 in the cylinders if I apply full brakes at that time as the pipe is already close to that value because I have applied and released full brake many times and very quickly before. Even if my equalizing reservoir is set to 90 (standard full release target) the pipe did not had time to be filled with air, so 20 is now my limit and therefore the max amount of air I can command into the cylinders. If this happens in a downhill you will have problems as you could not brake enough when you need it or even have no brakes at all. That´s why it´s very important to use dynamic brake, monitor your gauges and do not use brakes like there´s no tomorrow.

    TS2Prototype-Win64-Shipping 2021-02-15 01-05-44.png

    Another important topic is the brake overcharge that is available in some brake levers (in german locomotives there´s sometimes a switch in the desk for it). This is also simulated in game. As the operating pressure of brakes presents some tolerances, sometimes the brake valve of a vehicle does not set this operating pressure exactly as the one of another vehicle. Therefore, after coupling/decoupling or starting a service in some cases you may notice that brakes are not fully released. There you need to overcharge brakes to force a complete release. This is very frequent in the old british engines even while driving but I have used it in the german Dostos as well in some cases.

    Cheers
     
    Last edited: Feb 15, 2021
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