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View Diary: More Mystery Surrounds Canadian Ghost Train: Where are the locomotives? (160 comments)

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  •  Except That... (3+ / 0-)
    Recommended by:
    jrooth, science geek, Wreck Smurfy

    Your scenario is vaguely plausible, except that assumes the braking system was designed by idiots.  Requiring continuous air pressure to be maintained to keep the brakes engaged is just stupid.

    It also doesn't explain how the locomotives apparently:

    1. Became cleanly uncoupled from the rest of the train (this never happens; when one car falls off the track, it drags its neighbors with it);
    2. Escaped all apparent damage;
    3. Rolled uphill for a bit after passing through town and then stopped on its allegedly failed brakes without rolling back in to town.

    Again, nothing we've been told so far makes any sense.

    •  No, not stupid (5+ / 0-)
      Requiring continuous air pressure to be maintained to keep the brakes engaged is just stupid.
      that's why trains have handbrakes - so when the freakin' thing is shut off, it can be secured by a second mechanism.
      •  When pressure is OFF, brake is ON (2+ / 0-)
        Recommended by:
        Sychotic1, Roadbed Guy

        With compressed air braking, such as these and all north American trains have, the brake is OFF until pressure is applied, i.e. pumped up.
         These can be circumvented by the hand brake which loosens the brakes individually on the car, say in times when you WANT the car to move by itself.

        Happy just to be alive

        by exlrrp on Thu Jul 11, 2013 at 05:05:31 PM PDT

        [ Parent ]

        •  maybe not...not like semis...nt (0+ / 0-)

          This machine kills Fascists.

          by KenBee on Fri Jul 12, 2013 at 01:00:25 AM PDT

          [ Parent ]

        •  Your title, which is (0+ / 0-)
          When pressure is OFF, brake is ON
          isn't fully compatible with the (more correct) statement in the body of your post:
          the brake is OFF until pressure is applied,
          I think what confuses people is that the locomotive supplies "line pressure" which does two things

          1) it pumps up a reservoir in each car, which can be used to apply the brakes on that car when needed

          2) it acts as a sensor that in effect keeps point number 1 from happening while a train is operating normally.

          But when line pressure is lost (say, the locomotive is turned off or the cars become detached from the locomotive),  the line pressure is lost, triggering the reservoir in each car to release air to the brakes on that car and thereby apply the brakes.

          Therefore in a way it is true application of the brakes requires loss of pressure but that only applies in a indirect manner.  More directly air pressure (from the reservoir) IS REQUIRED to apply the brakes.

          OK, once the brakes have been applied this way, the reservoir is sufficient (usually!) to stop the train.  However, the air will slowly dissipate (in minutes or hours) - therefore if the handbrakes have not been applied and the train is on a grade, it will eventually start moving again.

          That's what happened here!

          Everybody in these threads keeps talking about how the brakes function in stopping the freakin' train.  That really has only minimal relevance (because the engineer had already done that!).  What IS relevant is how the train started moving again . . ..  ((which is explained a paragraph or two above).

    •  Loco heavier than a car? (0+ / 0-)

      The loco being quite a bit heavier than a car might not behave the same way.  We are talking about masses well beyond what we deal with in everyday life moving at 70mph.  If the car topples putting a twisting moment on the coupling why wouldn't the coupling just shear off.   Especially, if the loco has a lower center of gravity it will resist toppling more than a car which given most of its weight would be in the cargo it would be more top heavy and prone to tipping.  As compared to a car-car coupling where weights and center of gravity are approximately equal. So, loco-car coupling shears off, loco rocks but does not topple.

      Then, the only damage to the loco would be a broken coupling, assuming the loco did not have to crash through the cars.  Which given the comments about a switch being involved might have been the case.

      So:

      1) Toppling car shears off coupling. So, no apparent damage except to coupling.

      2) There is something about a switch being involved.  That could provide a force to direct cars away from the loco.  Although this requires locos to have jumped the switch or destroyed it.  Which seems plausible given the masses and velocities involved.

      3) Failed completely or failed enough to provide insufficient braking to counter the gravitational force of the cars.  But enough to hold just the loco in place.

      Completely speculative, but the point is that this much mass at the velocities involved and the materials involved just don't behave intuitively.

    •  I agree, ewhac. And here's the other thing (2+ / 0-)
      Recommended by:
      auron renouille, Joieau

      that doesn't make sense to me.

      Look at the chart at the top of the diary. The difference in elevation between Nantes and Lac Mégantic is 373 feet, or about 125 metres. This grade is over a distance of 13.1 km, or 13,100 metres. According to my calculation, that's a grade of a bit less than 1%, on average. That's hardly a "grade" at all. If you were walking it, or bicycling, you'd never notice it.

      Now I understand that once the train was in motion, with no brakes, gravity would have done its thing, since rails and railway wheels are close to frictionless. What I can't understand is how the runaway could have started on such a minimal grade, if even just a few of the handbrakes were set.

      -8.38, -7.74 My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world. - Jack Layton

      by Wreck Smurfy on Thu Jul 11, 2013 at 05:07:18 PM PDT

      [ Parent ]

      •  Not having been there, I suppose that it's (2+ / 0-)
        Recommended by:
        Joieau, Sychotic1

        possible that the siding it was parked on (assuming it was on a siding at all - after all, it would otherwise block the tracks while he was off duty) is on a grade larger than 1%.  It strikes me as insanely stupid to allow a sliding to have any kind of grade - why give gravity an advantage over you when sidings inherently will contain parked trains?  Even in the absence of a catastrophe, a graded siding would wear down brakes.  I would think that a rational builder would take the necessary steps to ensure that areas with parked trains are either perfectly flat or, if sloped, are sloped in such a direction to cause a train to come to rest against a block (e.g. the enormous heavy mechanisms that you can see in subway and commuter rail termini - I can't think of the term atm).

        Having said that, I'd say that the siding had to have had enough of a grade to allow the train to begin to move.  I mean, I'm going to assume something got it started here, I haven't heard of any Bigfoot sightings there.  Anyhow, basic physics - objects at rest, in the absence of some force (gravity, most likely) will stay at rest.  In the absence of gravity, there was no force.

        And that would just add to the insanely bad luck here.  Obviously, something went wrong with the brake, either mechanical failure or human error, but other than that, this is just such a bizarre situation that I don't think much will be learned from it, simply because it contains a series of events that seem unlikely to repeat in this precise fashion.  Maybe we'll get new zoning ordinances in some jurisdictions that say that you can't build propane storage or gas stations next to curves in railroad tracks or other places where a derailment could send a train car into a populated area.

        "The first drawback of anger is that it destroys your inner peace; the second is that it distorts your view of reality. If you come to understand that anger is really unhelpful, you can begin to distance yourself from anger." - The Dalai Lama

        by auron renouille on Thu Jul 11, 2013 at 06:00:32 PM PDT

        [ Parent ]

        •  Unlikely they'll ever go back (0+ / 0-)

          and rebuild the beds/railway tracks anywhere in North America in our lifetimes, maybe in forever. But you're right about 'something' setting the thing in motion, not even Bigfoot is big enough to start a train rolling on a 1% grade, though. Trains are seriously heavy beasties. As in a thousand tons or more (just the engines are ~90+ tons apiece, plus loaded tankers/cars at up to 140 tons apiece). That's some serious inertia at relative rest, you can't start it rolling just by pushing on it with all your muscles. Even if Bigfoot brought the whole family.

          I am not buying the 70 mph assumption (in comments here). Momentum of that much mass in motion doesn't need that kind of speed to wreck spectacularly upon a coupling switch gone bad. They filmed the movie The Fugitive near here, some of the most impressive footage of derailment ever - 2 locomotives and 4 empty cars (pushed from behind). That sucker wasn't going more than 40 mph.

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