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
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
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
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.
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.
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.
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.