Why Can't The Train Brake become the Engine Brake?

MarkInLA Jan 22, 2017

  1. MarkInLA

    MarkInLA Permanently dispatched

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    Through the 5 decades I've been a MRR I'm a tad ashamed that I either don't get something in the steeplechase of locomotive-braking discourse, air pressure/ glad hand app.? Or, have I in fact stumbled onto a control idea which is in place, or is on the drawing board somewhere as I type ? Look, just as universal the Westinghouse triple valve meant to creating George's air-braking system, why not/why can't this be done, too? Put another way, why can't an engine running lite, deadheading, be made to stop with the train brake, no need for separate engine brake ? Is it possibly dynamic-braking related ? (not that i'm complaining, mind you). Thanks for your interest....M
     
  2. Xmtrman

    Xmtrman TrainBoard Member

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    I'm not a railroader but I know one reason the independent brake is separate from the train brake is to allow the engineer to use it to "bunch the slack" in the train by braking the engine without braking the train.

    Also, if only a small amount of braking effort is required, it is much easier to to do it with an independent application, since using the whole train requires a lot more air pumping to release fully than does the independent.
     
  3. badlandnp

    badlandnp TrainBoard Member

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    Generally speaking, the Trainline or Automatic air is used for train control. Applying a small 5 or 10 pound set can keep the slack drawn out and helps to control speed on down grades and undulating small hills. In todays service with DP units on the end, the slack is kept bunched up, so I am sure that this has changed some.

    The independent does only control the locomotive(s) brake without any effect to the train. Generally, the independent is ineffective in slowing a moving train of any size. It is useful in holding a train parked and can be used to bunch a train that is in forward movement.

    In most freight locos, the dynamics may not be used with the air brake. There is a safety reason for this in protecting the dynamics. The exception to this is in passenger service where an expensive to install Blended Braking system is used. This allows for some use of dynamics and Automatic air simultaneously. However, the more air you set on the trainline, the lower your dynamic effect will be as the control system will reduce the amps of the dynamics.

    Remember, the air pressure on the trainline is at 130-140 pounds to keep the air released. A 'set' is also a 'reduction' of this pressure, which reduces the trainline pressure. This applies some braking to each car.
     
  4. BnOEngrRick

    BnOEngrRick TrainBoard Member

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    There are generally 2 types of air brakes on trains; "Automatic", which is the train air brake system and the "Independent", which is which is the locomotive air brake system.

    Every locomotive's air brake is tied into the train brake system. When an engineer makes a reduction, the brakes on the locomotives apply along with those on each car in the train. The engineer has the ability to "bail off" or "Actuate" the application on the locomotives separate from the train. On locomotives equipped with dynamic braking, there are 2 systems which control what happens regarding control with the independent brake; The Independent Pressure Switch will reduce dynamic braking force when a certain pressure is exceeded when the engineer applies the independent brake (usually above 15#). The Dynamic Brake Interlock provides an automatic actuation of the locomotive brakes when an trainline (Automatic) brake reduction occurs.

    Brake pipe pressure on freight trains is generally 90#. Passenger trains 110#. Some yard and switching operations are 80#. The reservoir pressure is normally maintained between 120-140# to provide adequate reserve for controlling air brakes. Locomotive brake pressure signal air is 45#. Depending on the type of "J" valve a locomotive has, the maximum brake cylinder pressure available will be between 32# and 72#.
     
  5. badlandnp

    badlandnp TrainBoard Member

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    Thanks for the clarifications. I am coming from the experience of remanufacturing locomotives and just talking to engineers. That means no actual practice. It has been a few years since I have been active in that field. We installed Blended Btaking on NJT and MARC units when I worked in Boise, and I never got to see that system in action. Any clarification on that system?
     
  6. BnOEngrRick

    BnOEngrRick TrainBoard Member

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    I have a friend that works for Amtrak and he uses blended braking all the time. He's tried explaining it to me but I can't grasp it until I see it in action.
     
  7. MarkInLA

    MarkInLA Permanently dispatched

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    Thanks for all the astute replies...They are quite informative. But I'm not sure anyone has answered my OP. You've pointed out when the 2, 3, or 4 braking aps that there are, are applied. Please answer why though that the train-brake lever can not become the independent brake so that cabs have only one brake lever which can become one or the other type...(perhaps by throwing some vertical lever to make the swap, say). Sorry if it's a lame idea....M
     
    Last edited: Jan 31, 2017
  8. Randy Stahl

    Randy Stahl TrainBoard Supporter

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    The train brake (automatic) will apply the locomotive brakes. Bailing or actuating the independent is optional consistent with good train handling.

    Blended brakes simply blend the air (automatic) and the dynamic brake in proportion to the amount of brake application.

    Randy
     
  9. badlandnp

    badlandnp TrainBoard Member

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    I think that the answer to your question in the OP is rather simple. The two brake handles are different and this is to help the crew know what's what. And, the plumbing to make such a change internally would be more complex than what is already a complex system.

    Keeping things as simple as possible is always a good engineering principle.
     
  10. RailMix

    RailMix TrainBoard Member

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    A former engineer told me that another use of the engine brake is to hold the train while pumping up the train line, which would also require the engine brake to be independent.
     
  11. MarkInLA

    MarkInLA Permanently dispatched

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    Thanks once again to all.. Aside from the other considerations, Tom's and Alan's (above) make the most immediate sense that I'd never thought of...M
     
  12. Charlie

    Charlie TrainBoard Member

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    I agree with what all the other engineers have said about braking. On the BNSF we use the independent during yard switching since cars are generally not switched with air. The METRA locomotives I ran in commuter service have a blended brake system with a quick release ability. It works real well especially since we have 26 station stops on the Chicago-Aurora "racetrack" and every station platform has a different "spot". Some guys like to call the independent brake "the parking brake".

    Charlie
     

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