I have some fascination with trains, but don't know a whole lot about them. In a broader scale, my interest in them extends in large part from my fascination with transport accident/losses. I continually read loss reports from all aspects of transportation, my most informed area of which is aircraft operations. Train ops are a big unknown to me.
I was just re-reading a detailed summation of the events leading to the Lac-Mégantic rail disaster, where the train loaded with Bakken crude rolled down the grade and derailed in town with resulting fire and explosions. And a couple of simple general questions I'd had before resurfaced, I figured I could ask here and get some informed answers.
First is that the engineer apparently shut down because one engine was having mechanical problems, a poor engine repair was causing an extreme blow-by condition and it was consuming a lot of oil and discharging it from the stack as both smoke and oil mist.
He'd mentioned to the cab driver who picked him up from where the train was parked that he felt uncertain about leaving it running to provide brake air supply with the engine compromised in such a way.
What I wondered, was apparently this engine was one of five, so why'd he need to leave THAT one running? There must be a simple answer, as it's too obvious that he could have let a different one idle. All I can think of immediately is perhaps the arrangement of how the power units were ganged for control purposes prevenets this, i.e. the damaged unit was the "master" and had to be running if any of the others was operating?
Next question. I'm famailiar with air brakes, as a former truck driver. But apparently train air brakes are different. With big trucks, there's two air lines, one that is high pressure supply, and one low pressure signal line. Very powerful springs in the brake diaphragm cans try to apply the brakes continuously, that supply of high pressure air is modulated by the signal line pressure, so that when moving, the high pressure air is holding the springs at bay and allowing wheel movement. When you apply the brakes, the signal pressure causes the control assembly to reduce the high pressure side, allowing the springs to apply the brakes.
In this set-up, if the brakes have no high pressure air supply, they default to the fully applied state. In other words, that truck will not move if there is no air pressure present in the system. This makes certain that an uncoupled trailer will not move, and a non-running truck cannot roll away.
But apparently train brakes are a bit more primitive, with high pressure air applying the brakes, and mechanical manual devices to set the brakes on each individual train car, for the purposes of parking or immobilizing a decoupled unit.
Actually, in the course of typing this, it occured to me that having its natural state be a "roller" is probably necessary for the purpose of humping and maybe other operations? I may have answered my own question...but it does seem to me that I kind of like the safety aspect of brakes that want to hold if something goes wrong or the vehicle is umpowered....
Anyway...love to hear any and all apects of why it's done the way it is. Thanks!
Do a search for Lac Megantic in the Search the Community box and you will get all the answers (good and bad) that you can spend hours trying to understand. One thread to start you on your way
http://cs.trains.com/trn/f/111/t/218974.aspx
Never too old to have a happy childhood!
For an understanding of railroad air brakes, try this version of Al Krug's well known air brake primer:
http://www.alpharail.net/sumpter/sumptertraining/Air%20Brakes%20for%20Dummies.pdf
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Jeffco67,
The engineer stopped and left the train at Nates because he was at the end of his shift on duty, not because of the mechanical problems with the lead locomotive. You are right about the mechanical problem allowing a form of blow by that carried lube oil to the top of the piston. It was reported as a hole in one piston. I assume that cylinder was not firing, so it conducted lube oil and diesel fuel into the exhaust manifold.
I know of no reason why the engineer could not have shut that engine down and started another. He would have had to make a few changes to change another engine to the operating cab. It seemed by the news report of the conversation with the cab driver, that the engineer had been told to simply leave the locomotive running as it was rather than shutting it down and changing to another one as the controlling unit. Perhaps he was out of time for his shift.
Train air brakes offer the same functionality as truck air brakes, but the details of the system are different. With train brakes, air does the work of setting the brakes, and it also does the work of transmitting pneumatic signals to control that setting and releasing. One brake line carries both functions. Like a truck with its springs applying the brakes, if there is no air, train brakes too are failsafe in that regard.
They default to the applied state if there is a loss of trainline (or brakepipe) air. They are able to do that because it is not the trainline that is pressurized to directly activate the brake cylinders. The air that accomplishes that is stored in a reservoir on every car. The trainline or brakepipe, is used as a supply line to charge the car reservoirs, and then it is used as a control line to release air from the reservoirs, and letting that stored air activate the car brake cylinders. This air brake system for the whole train is called the “Automatic Brake.” There is also a separate air brake system just for the locomotives called the “Independent Brake.”
There are also completely manual hand brakes that you set and release for securement, acting like parking brakes. For yard switching operations, the cars are typically made into free “rollers” with no air brakes in operation, as you surmise. In this mode, the trainline is exhausted by uncoupling it from the locomotive, and leaving the anglecock open to atmosphere. Initially, this causes the car brakes to completely set, but then the reservoir and cylinder are bled by a manual bleeder valve on each car, leaving the car totally without air.
Leaving the automatic or independent brakes set to secure an unattended train is considered unreliable, and it is against the rules. Unattended trains must be fully secured by the proper number of hand brakes without any reliance on either automatic or independent air brakes. After setting the prescribed number of hand brakes for a given location, a push/pull test must be performed as a practical check that the hand brakes will hold the train in place.
In the Lac Megantic incident, the engineer did not set enough hand brakes to hold the train. He achieved the adequate securement by a combination of hand brakes and the independent air brakes. As I recall (if I am not mistaken), he did do a push/pull test, which was successful, but the success relied on the holding power of the independent brakes to supplement the holding power of the hand brakes. So when the engine was shut down, the independent brakes leaked off and the train rolled away despite the hand brakes.
So yes, he could have shut down the bad engine and started another one to maintain air pressure; but in the larger perspective, he should not have been relying on air pressure at all.
Jeffco67
Welcome to the forum
Thanks to all and you in particular for a detailed response. That answered my nagging question about how these brakes operate.
Don't know all the details of the run away oil train up north but do know one or more engines could have been left running in the consist to supply air assuming they were not equiped with "Smart-Start" which would only start an engine when the air in the reservior became depleted below 90 pounds (brake pipes usually are set to this pressure). I can tell you that railroad air brakes are a closed system which operate on pressure differential within the control valve. The Brake Pipe is charged troughout the train to a pressure set by a manual feed valve located in the controlling cab (usually 90 psi). When the automatic brake valve is moved from running to apply the Brake Pipe pressure drops and that causes the control valve on the car to move and allow an application to the brake cylinder. The amount of reduction determines the application to the car brake cylinder. That cylinder extends a piston and through a mechaical connection multiplys the cylinder's pressure greatly in terms of braking force where the brake shoes contact the wheel tread. When the BP is restored, the apllication is vented to atmosphere and the control valve will recharge the car air reserviour to the point of equilization with the BP. On modern equipment, there is a maintaining feature which sense leakage during a set and replinishes the BP but below the rate which would cause the car control valve to go to release. Locomotive air brakes are all straight air through a seperate feed valve. The two systems are tied together in the locomotive distributing valve so that an automatic train brake application also applys the engine brakes which must be manually overridden by the Engineer in the cab when he depresses a bail feature on his independent engine brake valve to avoid adverse slack generated by his engine brakes againtst the train. That is pretty much how it works.
Richard Benton
Retired Locomotive Engineer
Euclid I know of no reason why the engineer could not have shut that engine down and started another. He would have had to make a few changes to change another engine to the operating cab. It seemed by the news report of the conversation with the cab driver, that the engineer had been told to simply leave the locomotive running as it was rather than shutting it down and changing to another one as the controlling unit. Perhaps he was out of time for his shift.
Euclid, and Euclid only, please tell us why he would have had to change operating cabs if he had shut down the lead engine and started up a trailing unit.
Jeff
jeffhergert Euclid I know of no reason why the engineer could not have shut that engine down and started another. He would have had to make a few changes to change another engine to the operating cab. It seemed by the news report of the conversation with the cab driver, that the engineer had been told to simply leave the locomotive running as it was rather than shutting it down and changing to another one as the controlling unit. Perhaps he was out of time for his shift. Euclid, and Euclid only, please tell us why he would have had to change operating cabs if he had shut down the lead engine and started up a trailing unit. Jeff
I don't know what exactly would be required to shut down the bad engine and start another one. At some point in earlier discussions, we were talking about why they did not take the time to do that. In the course of that discussion, someone said you need to change to make another unit the controlling unit, but that would not take much time. What would you need to do and how much time would it take?
It seems as if the engineer wanted to shut down the bad engine, but was overruled by his supervisors. That was indicated by his coversation with the cab driver.
Before the Lac M incident, in Canada, depending on the railroad it was common practice and actually THE RULE to ONLY use the air brakes when leaving a train as long as the lead engine was running and you left the handle in full service.
Before that we NEVER put handbrakes on the train when leaving them.
The MMA may have had this rule.
10000 feet and no dynamics? Today is going to be a good day ...
traisessive1 Before the Lac M incident, in Canada, depending on the railroad it was common practice and actually THE RULE to ONLY use the air brakes when leaving a train as long as the lead engine was running and you left the handle in full service. Before that we NEVER put handbrakes on the train when leaving them. The MMA may have had this rule.
That seems like astouding information in the wake of the all of the discussion about securing trains and how it related to the Lac Megantic runaway. What was the theory that made that reliable? I guess it was assumed that the set automatic brakes would not leak off very fast compared to what happened at Lac Megantic. With that runaway, the automatic was fully released.
As I understood it, handbrakes and a push/pull test were required for the Lac Megantic train that ran away, and no reliance on air brakes was allowed.
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