Quote from: Speeddog on July 10, 2013, 01:20:24 PM
Oddly enough, in searching for how train brakes work, Wikpedia had this reference:

http://www.reuters.com/article/2013/07/09/us-train-narrative-insight-idUSBRE96801Q20130709

Best explanation I've seen yet on how this unfolded.
But didn't explain the apparent lack of truly fail-safe brakes.

This:
https://en.wikipedia.org/wiki/Railway_air_brake

Explains how the Westinghouse air brake works.

Apparently, it's only fail-safe as long as there's air supplied under pressure.
And only functional as a parking brake if it's a two-pipe system.

I find that odd.  Considering tractors (tractor trailer tractors) and straight trucks with air brakes have a safety that can't fail because of lack of air.  On a modern (within at LEAST a couple decades, likely more) truck. with air brakes the actual parking brake is a spring system that holds the brake shoes in place.  It takes at least 60 PSI of air to hold back the spring-loaded parking brake.  That means two things:  1.  A lack of air pressure means the parking can't be removed unless you manually get under the vehicle and back the shoes off like old-school drum brakes and 2) A lack of air pressure should have automatically LOCKED all brakes in the system, because once the air pressure in the air system is too low to hold off the spring brakes, the spring brakes slam on and hold. 

Cliff notes:  On most modern air brake systems, A cut airline results in the parking/emergency/spring brakes being applied unless they are manually backed off (time consuming and often requires special tools)...

JM

Quote from: the_Journeyman on July 10, 2013, 01:45:11 PM
I find that odd.  Considering tractors (tractor trailer tractors) and straight trucks with air brakes have a safety that can't fail because of lack of air.  On a modern (within at LEAST a couple decades, likely more) truck. with air brakes the actual parking brake is a spring system that holds the brake shoes in place.  It takes at least 60 PSI of air to hold back the spring-loaded parking brake.  That means two things:  1.  A lack of air pressure means the parking can't be removed unless you manually get under the vehicle and back the shoes off like old-school drum brakes and 2) A lack of air pressure should have automatically LOCKED all brakes in the system, because once the air pressure in the air system is too low to hold off the spring brakes, the spring brakes slam on and hold. 

Cliff notes:  On most modern air brake systems, A cut airline results in the parking/emergency/spring brakes being applied unless they are manually backed off (time consuming and often requires special tools)...

JM

True, I have seen many times on "Ice Road Truckers" when the air lines even freeze, the brakes lock up. Didn't think of that till now.

Frozen brakes suck.  It's either the won't release & you can't move or they release and every time you hit the brake pedal it's whiplash.  Frozen brakes suck.

JM

quote from popular mechanics

The air brake protects against a runaway train like the one that barreled through the small town of Lac-Megantic, Quebec, on Saturday and derailed, its cargo of crude oil from North Dakota bursting into flames and engulfing the community's downtown in an inferno that killed at least 15 people. In the immediate aftermath many are asking how the train's air brakes could have failed so disastrously. But how do they work, anyway?

In some ways, a train's air brake is a lot like the brake on your car. In your car, slamming on the brake pedal transfers your foot pressureâ€"through brake fluidâ€"to a piston, which clamps a pair of pads tightly over the brake disk in your car's wheel. Air brakes also use pressure to squeeze the moving railcar's wheels to a standstill. But instead of brake fluid, they use compressed air.

Rex Beatty, a conductor for 35 years and the president of the Teamsters Canada Rail Conference, says that today each train car has an isolated air tank filled with pressurized air. As a failsafe, this air reservoir is constantly supplying the pressure needed to brake the wheels. "So when you pull the brake on the train, you're just using that reservoir in the car," he says. "That's how you get the brakes."

Essentially, the brakes are always on. For the train to actually move, the operator has to disconnect this air tank. He or she does this by pumping air into a separate line called the brake line, which switches a valve to separate the tank from the brakes. And as soon as the brake line stops delivering pressure, the valve automatically flips back and reconnects the air tank, engaging the brakes.

The beauty of this system is that, in normal circumstances, it requires pressurized air for the train to move. In the old days, a single leak could make a train lose all its pressurized air, and it wouldn't be able to stop. Today "if you lose all your air," Beatty says, "the brakes will automatically [activate]." And if one of the air tanks somehow malfunctions, the rest of the train can compensate because each car has its own.

So how could the disaster in Canada have happened?

The only danger with air brakes is if all the air tanks lose pressure. Beatty says that because of unavoidable leakage, the tanks are always gradually seeping air. "Air can leak around the piston and can leak through the various connections between each car," Beatty says, "but there will eventually be leaks." Normally, the train's engine is constantly resupplying the railcar's tanks with air, and this slight leakage isn't a problem.

But trains parked for an extended period of time rely on hand brakes which, just like the old days, are manually engaged at the back of each railcar. This anchors the locomotive without relying on its airbrakes, whichâ€"without a running engineâ€"are gradually losing their power. And when the train starts back, the operator won't move the train without making sure the air tanks are refilled.

Investigators have not released details about the Quebec train derailment, but it's probable that for some reason, the air brakes were left on too long without engaging the individual cars' hand brakes. When firefighters responded to a blaze and shut off the train's running engine, the locomotive might have eventually lost pressure in the air tanksâ€"and lost its stopping power. This could have caused the train to roll away and gain speed, resulting in the disaster this weekend.

The true cause of the Quebec train derailment won't be known until officials complete their investigation, but properly used, air brakes have been reliably stopping trains for almost 150 years. "I found the air braking system on trains very safe and effective," Beatty says, "but like everything else, it involves certain procedures that need to be followed."

Good info to know.  I wasn't 100 % sure how train air systems were different from semi trucks.  Seems they're plenty different.

JM

My best friend from HS is a retired hoghead (locomotive engineer), Denver & Rio Grande Western RR.
It's even more interesting, there is a lag from the time you move the brake lever in the lead engine until the brakes actually start slowing you down, also there is a lag when releasing the brakes. Plus the train brakes are separate from the engine brakes and you have dynamic brakes (using the traction motors as generators and dumping the power into resistor banks).
In rolling hill country half way down a hill you release the brakes, just before the lead engine gets to the bottom apply power. The brakes in the back half of the train are still on even through the lever is in the off position. All a matter of timing and experience.
Just before cresting a hill, reduce power, 1/4 to 1/3 of the way down apply brakes. Remember the back half is still going uphill.
Done well it's a thing of beauty, done poorly = snapped drawbar which breaks the air hose, locking up all the brakes.

I never thought of the slinky effect in rolling hill country. I can definitely see how conducting in these conditions can be an art.

Quote from: scaramanga on July 11, 2013, 02:10:06 PM
I never thought of the slinky effect in rolling hill country. I can definitely see how conducting in these conditions can be an art.

Two slinkies, the slack in each draw bar, (1 to 2 feet X 100+ cars = a lot of slack), and the mile long air pipe that works the train brakes.
Back in the day when trains still had cabooses, the engineer could radio back and have the rear brakeman apply the air brakes from the caboose. Coming into a station with a passenger train, by having a gentle brake application from the rear you come to a smooth jostle-free stop.

Quoting from the Reuters article:

"He secured the train at 11:25 p.m. on Friday, setting the air brakes and hand brakes, according to MMA. Burkhardt said the engineer set the brakes on all five locomotives at the front of the train, as well as brakes on a number of cars, in line with company policy. Four of the train's engines were switched off, but the front locomotive was left on to power the airbrakes. The engineer, who Burkhardt declined to name, then retired to a hotel in Lac-Megantic.

Soon after, things started to go wrong. Nantes Fire Chief Patrick Lambert said the fire department got a call about a blaze on one of the locomotives at 11:30 p.m. He said the fire was likely caused by a broken fuel or oil line.

Firefighters reached the scene within seven minutes.

"It was a good sized fire, but it was contained in the motor of the train," Lambert told Reuters. "By 12:12, the fire was completely out."

But as they extinguished the fire, the 12 volunteer firemen also switched off the locomotive, in line with their own protocols, to prevent fuel from circulating into the flames.

One of the many unknowns in the story is precisely what happened next.

Lambert said the fire department contacted the railway's regional office in Farnham, Quebec, and spoke to the dispatcher. "We told them what we did and how we did it," Lambert said. "There was no discussion of the brakes at that time. We were there for the train fire. As for the inspection of the train after the fact, that was up to them."

It was not known what the dispatcher did after receiving the call. Burkhardt said he was not sure if the dispatcher was told that the engine had been shut down, or what the dispatcher did after receiving the call. The company is still investigating the incident, as are Canadian authorities."

1. Engineer locks up according to protocol (1 locomotive running to power brakes, handbrakes set every so many cars, etc...) and leaves the train.
2. Fire breaks out but is contained
3. Firefighters switch OFF locomotive that powers air brakes to prevent more fires/damage according to their protocol
4. Firefighters contact railway and notify of events.
5.

Did the firefighters notify the dispatcher of shutting off the locomotive? Did the dispatcher understand the importance of not having a locomotive running and contact the Engineer? Did anyone give a flying f%$# enough to bother making sure everything was fine?

Let me re-quote  Fire Chief Patrick Lambert:  "There was no discussion of the brakes at that time. We were there for the train fire. As for the inspection of the train after the fact, that was up to them."

I'm not criticizing firefighters, far from it, not based on one article, and especially not when 19 of them died recently. But I think they should have taken the time to follow things through to make sure everything is done right, to make sure the dispatcher is aware and the engineer is awake and has been informed of what's happened. For that matter go the extra yard: go pick up the guy and get him to his train. That would have saved 50 lives and prevented all this destruction. Rant off.

"Did anyone give a flying f%$# enough to bother making sure everything was fine?" 

I think... FWIW... that your rant is spot on TMKP.

However, if the hand brakes were set as well, even if the locomotive was no longer supplying air, it's my understanding the train should have stayed but.  I'm not 100% certain, but I was thinking the hand brake was mechanical setup and didn't require air.  Maybe someone familiar with train cars can chime in on the hand brake setup.

JM

Seems that the statement by the engineer that he set the handbrakes isn't ringing true.....

http://www.nydailynews.com/news/world/engineer-faulted-quebec-train-crash-article-1.1395366

Quote from: Speeddog on July 12, 2013, 11:13:26 AM
Seems that the statement by the engineer that he set the handbrakes isn't ringing true.....

http://www.nydailynews.com/news/world/engineer-faulted-quebec-train-crash-article-1.1395366

Results of an internal investigation. 

I'd hate to think an engineer would not set the manual brakes and then lie about it but it can't be ruled out.

Myself being a bit of a skeptic, I'll wait to see what an independent investigation reveals. 

On a related note, does Canada have a version of the NTSB?

Quote
On a related note, does Canada have a version of the NTSB?

yes we have Canadian Transport Safety Board.
The Provincial Police is also conducting a criminal investigation.