# Tech question about train brakes....



## Brakeman Jake (Mar 8, 2009)

As most probably know,a terrible accident involving a train happened in Lac-Megantic (Quebec) friday night.Estimated casualties should be around 48 people.

Obviously,there's a lot of questions as to what has caused such an event but most of the findings so far definitely lead to an inappropriate use or defective condition of the train's braking system.What seems to be the most probable cause is the fact that because one of the engines (there were five) was stopped by firemen to control an on-board fire,the air supply to the brake system went down,thus releasing the brakes with the following tragedy.

Now,that theory doesn't fit in my mind.I've worked with air brakes most of my career (trucks of all sorts) and unless train brakes don't work the same way,this doesn't seem possible to me.What seems obvious is that the crew who parked the train had stopped it using the "service" brakes alone so that pressure was required to keep the train stopped.Obviously,stopping the air supply (shutting the engine+air leaks) would lead to this horrible event and that's likely what happened.

Where I don't get it is why the "parking" brakes didn't step in.In trucks,when the air pressure gets lower than + or- 80 PSI,parking brakes (or Maxi-Brakes) automatically engage and you need to supply air pressure to release them.The result is simple...no air no move.

Word is that the loco had been left running to supply air to the brakes...wouldn't have been much simpler (and safer) to apply the parking brakes before leaving the train?To my knowledge,all locos and cars do have a parking brake system........Can someone explain this one to me?.....


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## cv_acr (Oct 28, 2011)

Brakeman Jake said:


> Where I don't get it is why the "parking" brakes didn't step in.In trucks,when the air pressure gets lower than + or- 80 PSI,parking brakes (or Maxi-Brakes) automatically engage and you need to supply air pressure to release them.The result is simple...no air no move.


Doesn't work the same way with trains. Air pressure in the reservoir is required to apply the brakes. If the engines all got shut down somehow, eventually the air will slowly bleed off and the air brakes will eventually release.

It's designed to be somewhat failsafe IN OPERATION, in that a drop in air pressure in the train line causes the control valve to apply the brakes using the air pressure in the reservoir. The reservoir gets repressurized by the train line, so if the brakes are applied and there's no pressure in the train line anymore, it's possible for the pressure to all bleed off after a while. That's why handbrakes are supposed to be applied on cars left sitting on spurs as they won't have air brakes anymore. It's a bit different for a standing train, but one would kind of think that some handbrakes should be applied as a backup.



> Word is that the loco had been left running to supply air to the brakes...wouldn't have been much simpler (and safer) to apply the parking brakes before leaving the train?To my knowledge,all locos and cars do have a parking brake system........Can someone explain this one to me?.....


The "parking" brake is a handbrake. It must be manually applied/released (on individual cars). There's been no information released as to if or how many handbrakes were applied when the train was tied down, so anything is just speculation at this point.


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## Brakeman Jake (Mar 8, 2009)

So if I understand this right,it is usual for train crews to simply apply air brakes and leave the train with the engine(s) running under no supervision whatsoever so incoming crew just jumps in,releases the brakes and go.

If so,last weekend has proven this to be highly hazardous to say the least.That is assuming (trusting) the engine won't quit by itself for any reason or no body will turn it off.In this case,firemen confirm turning the engine off,likely not knowing better as they wouldn't have been able to extinguish the fire with the engine running anyway.

Personally,my blame would go to the leaving crew that I believe should have waited for the replacement crew to arrive.I suspect they used to do this all the time but let's guess this will change in the future.

Another point that tickles me somewhat...one of the other four locos could have been substituted to the damaged one to keep air supply to the train,I suppose.Seems none of the MMA employees who were there thought of this either.

We'll know someday what happened.Right now,it pretty much seems like a lack of communication,ignorance,unappropriate company procedures and may be some carelessness may have joined to cause this terrible incident.


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## cv_acr (Oct 28, 2011)

It's not that uncommon to tie down a train without a crew outside of a yard somewhere for various reasons usually due to crew changes or crews hitting their maximum hours on duty. (Or maybe just a full yard? I've seen a train tied down for the night just a few miles from its actual destination before.)

I wouldn't blame the leaving crew simply for leaving. If he followed the railroad's standard procedure for tying down the train, it's not his fault. He did everything he was supposed to.

The new crew may not have been arriving until the morning.

Pointing fingers or identifying causes is pretty speculative yet at this point, but I wouldn't be surprised for the TSB investigation to take a hard look at the procedures for tying down the train (and I have no reason to suspect that MMA's procedures would be different than any other railway's - and no I don't work for any railway, so I don't really know the specifics) and whether handbrakes were properly applied and how many (again I don't have specific information on whether they were or not so this is _highly speculative_, but that should have prevented a rollaway).


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## ktcards (Sep 22, 2012)

Back in the day when my father was a conductor on the railroad they were allowed to work so many hours. When they exceeded their hours they were deadheaded and stopped the train wherever they were (even 40 miles from nowhere) and waited for a taxi to take them back to town.

Secondly, they never shut a diesel engine down. They are so difficult to get restarted and usually have to be jump started from another engine. Also many of them don't even have their batteries connected so they couldn't get started on their own if they wanted to.

R


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## Steve S (Jan 7, 2012)

Here's a website showing how the air brakes work. Scroll down a ways to see diagrams explaining it...

http://www.railway-technical.com/air-brakes.shtml

Steve S


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## Brakeman Jake (Mar 8, 2009)

Well,thanks for the info.My curiosity is satisfied.However,though proven quite reliable,the system has a major flaw in my mind...the train can be moved without air and this in my mind is dangerous,as a late event has proven.

I've worked in trucks for most of my career,and though their air brakes systems are somewhat more complex (two color keyed hoses and a few more valves),they are much safer in my mind at least.

Trains wouldn't need an as complex system (like ABS air brakes for instance) to be safe....simply rig the locos and cars with dual chamber brake boosters (one for service brakes and the second one spring loaded that you need air to release) like trucks have and a simple air supply valve dedicated for parking brakes alone.

Train operators wouldn't have to climb aboard every car they want brakes applied on as removing the air would apply them automatically on EVERY single car.A simple visual inspection on a few cars to confirm the system works and they could leave the train in total safety.And even if they elect to leave the loco running and supplying air to the brakes,a safety valve would automatically apply the park brakes.Climb in the loco,turn or push the parking brake valve,allow may be a minute or two to refill the air chambers and they'd be ready to go.

I always thought trains were like trucks...well I guess a major event has to occur for engineers to re-think a system.


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## gunrunnerjohn (Nov 10, 2010)

Well, I suspect that sometimes they don't want to brakes on all the cars, perhaps in the yard when building consist's.


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## MRLdave (Nov 1, 2011)

Jake...the problem with your system is that in a lot of instances, you DON'T want the brakes to automatically apply as on a truck.......for example in a hump yard. It's a little hard to get a car to roll down a hill if it's brakes are locked on. And the current system is better than the "old days" when the cars didn't have ANY air brakes.....workers had to run along the walkways and manually crank the handbrakes on each car if the loco couldn't slow the trail on it's own.....there was no such thing as a "panic stop", which is why they made the law up that the train ALWAYS has the right of way at crossings...if the train can't stop, then make everything else stop.


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## Brakeman Jake (Mar 8, 2009)

Very good point...hadn't though of this.But what if,let's say,locomotives had such safety brakes (that's feasible BTW),would it be enough to hold a train "halted"?I'd guess so in most cases and that wouldn't be a PITA for operators.


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## Big Ed (Jun 16, 2009)

Many moons ago I used to pickup chemicals in a facility that had 3 sidings for their tankers.
You would weigh in and get your paper work then drive to your tanker that you where going to load out of and wait.
The loaders would eventually come out and hook up hoses to the bottom and pressurize the tanker with nitrogen or air to load you up. It depended on the hazard of the liquid as to what they used to load you up.
The end of the rail was about 20 feet from the Newark bay in Jersey. One little bumper to stop it in case of a runaway. No derailers were used back then and no wheel chocks. 
When the train came in to spot the tankers they would only crank the brake to the car that was hooked to the locomotive. Maybe 20 cars would be held by the one braked car. The tracks looked level. 

One day they were having a meeting and it was taking forever for the loaders to come out.
The dope that was waiting by the braked car that held the rest for some reason released the brake wheel! I was waiting down by the end near the bay when all of the sudden the cars started rolling! The dope that released the brakes was running after them and luckily cranked the brakes right before it hit the little bumper.
The cars moved around 30 feet when the loaders came out they noticed right away that the cars had moved. I said I know/saw nothing, I was taking a nap while waiting. I knew the dope that released them. 

Even though the rails looked level I guess there was a little pitch towards the river it didn't take anything for the cars to start rolling!
If he didn't catch it they would have gone right into the drink!
After that they used wheel chocks and installed a derailer at the end. 

The rail yard where I pickup today uses wheel chocks made of hard rubber they are so small I don't know how it would stop a tanker from rolling.:smokin:
They are sort of like these but made out of a hard rubber. They don't have the handle on them. It looks like the wheels would just roll right over them if a locomotive started pulling the train out.









Something like this looks like it would secure the train better. 
It locks/clamps on the rail. :thumbsup:


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## gunrunnerjohn (Nov 10, 2010)

I think you'd be surprised how a very small chock would hold even a heavy load on a significant grade. You have to remember the wheel has to climb that hill, that takes a lot of energy.

Drive your car up to a small 1" bump in a curb, see how much power it takes just to go over it.


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## MRLdave (Nov 1, 2011)

I was at the Colorado Railroad museum this week, and they just wrap a length of chain around the wheel (in front, then behind, then across the back and hooked together on the outside to hold cars in place.


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## Big Ed (Jun 16, 2009)

gunrunnerjohn said:


> I think you'd be surprised how a very small chock would hold even a heavy load on a significant grade. You have to remember the wheel has to climb that hill, that takes a lot of energy.
> 
> Drive your car up to a small 1" bump in a curb, see how much power it takes just to go over it.



The little rubber chocks will hold them if no locomotive comes along and tries to move it. 

Read the last sentence of my post.
(It looks like the wheels would just roll right over them if a locomotive started pulling the train out.)

The first set of chocks would do nothing at all, the second set might as they are clamped to the rail.
As your last sentence says, "power" I think a Locomotive has enough "Power" to pull the wheels right over those little rubber chocks. Even the clamped ones might drag down the rail till they break off.


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## gunrunnerjohn (Nov 10, 2010)

Ed, I said nothing about a locomotive trying to pull the car over the chock, I was just observing that a chock on the car would probably hold it from rolling. I agree that a locomotive could probably pull through most of them. Maybe over, crush, etc., but 5,000 HP can do a lot of damage.


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## Big Ed (Jun 16, 2009)

gunrunnerjohn said:


> Ed, I said nothing about a locomotive trying to pull the car over the chock, I was just observing that a chock on the car would probably hold it from rolling. I agree that a locomotive could probably pull through most of them. Maybe over, crush, etc., but 5,000 HP can do a lot of damage.


I know I did. 
I said nothing about them holding cars stationary . 

I still would want the bigger clamped on chocks if it was my railroad.


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## gunrunnerjohn (Nov 10, 2010)

Well, when you get your own RR, you can park your BigBoy in front to keep the cars from rolling.


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## Big Ed (Jun 16, 2009)

gunrunnerjohn said:


> Well, when you get your own RR, you can park your BigBoy in front to keep the cars from rolling.


That would be cool huh? :smilie_daumenpos:

Though I would still use the clamp on chocks for that. 
Maybe 2 of them. :smokin:


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## T-Man (May 16, 2008)

The law of motion, an object at rest tends to stay at rest and an object in motion tends to stay in motion. Trains have mucho mass and take lots of power to get started. Therefore they need lots of power to stop. Brakes have only so much power so they make up for it by using distance. This is the same reason you never cut in front of a truck just before a stop. The truck may need that space to stop and you will be out of luck.

A wheel wedge just keeps a wheel from rolling at the start.


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