Train Brake System vs Semi Systems

According to this, trains have fail safe brakes and brake with a reduction of air pressure.

According to an investigation of the Lac- Megantic disaster in Canada, a loss of air pressure caused the brakes to release,resulting in a run away train going downhill and derailing causing the loss of many lives.

Perhaps their system was different?

http://www.cbc.ca/news/canada/montreal/lac-megantic-criminal-negligence-verdict-1.4474848

I don't know but according to your article, most of the case revolved around the 7 hand brakes that were applied to secure the train, whether they were tested by the engineer and enough to secure the train.

Here is some more info on theinvestigation:

"Harding left the lead locomotive No. 5017 running to keep air pressure supplied to the train's air brakes and also applied a number of hand brakes.^[51] Yves Bourdon, a member of MMA's Board of Directors, stated that the air brakes of all locomotives and freight cars had been activated, as well as hand brakes on 5 locomotives and 10 of the 72 freight cars."

Why was it necessary for the engine to maintain air pressure to keep brakes applied if they were "fail safe" when air is lost?

My understanding of the situation is that a fire started in the stack of the idling engine,and the fire department,following proper procedure,shut down the engine and turned off the main circuit breakers.This resulted in a loss of braking,which would not have happened in a properly designed fail safe system.

All brakes should have been applied when air was lost,making the hand brakes redundant,like the parking brake on a car.

With 72 sets of brakes applied,I don't think it would have rolled downhill.

https://en.wikipedia.org/wiki/Lac-M%C3%A9gantic_rail_disaster

"Why was it necessary for the engine to maintain air pressure to keep brakes applied if they were "fail safe" when air is lost?"

Unfortunately they are not totally fail safe.

The brakes have 2 circuits - the first is to keep a storage tank on each car charged with air in order to operate the brake.

A valve prevents this tank from releasing air to the brake cylinders whilst ever the pressure in the first circuit is above a set minimum.

Should the pressure fall due either to a broken pipe or deliberate activation of the emergency brake lever, then the brakes will be applied via the pressure retained in the tanks.

The second circuit is generally an electro pneumatically operated system which has a more rapid response time to braking requirements, but is not used for emergency braking. It controls the air to the tanks at each car rather than waiting for the pressure release via the locomotive which, in a long train can be very slow. The other problem removed by this method is that pressure release at the loco activates the brakes on the nearer cars first thus causing an overrun and pushing effect from cars further afield.

The failsafe bit is that a failure of air pressure in the first circuit either due to a broken pipe or deliberate activation of the emergency brakes will cause the tank pressure to be higher than the circuit pressure thus operating the brakes fully. Each car's tank is a separate entity and the air in each tank is isolated from others and only applies its own associated brakes. - which is good if they have sufficient air to do so.

The unfortunate part is that the tanks can take some time to recharge, especially after prolonged on and off operation of the brakes during a long downhill run.

I suspect that the loco was kept running to recharge these tanks.

If the tanks indeed had insufficient pressure, then the few parking brakes that had been applied may not have been enough to prevent the train from moving.

IHHO:

The system was not designed to be fail safe from the start,safety was added "ad hoc" style and resulted in a "Rube Goldberg" braking system by adding features to an existing system as the need arose.At all levels,safety was the last consideration.

I realize there are millions of rail cars in the USA,and the cost of maintenance is enormous,and it would require many $$$ to implement even a small change in all of the rolling stock,but what price human lives?A few pennies per mile would quickly pay for the changes.

As someone very aptly said:"The answer to WHY?" or "WHY NOT?" usually boils down to a common answer:MONEY".

Most railway systems are designed with safety at their core. The braking systems are typically also designed with safety at their core. BUT, there are also safe operating procedures to be followed - no system is idiot-proof. So no, without facts to my disposal, I would not agree that the air braking system is designed in a hodge-podge manner without safety in mind. I worked in the industry, and the safety focus from a design perspective is at an extremely high level! It is implied that the train driver/engineer left the train idling (otherwise he would have told the firefighters what to do) - now THAT seems crazy...

Even truck brakes are not fail to safe - if you don't use them correctly, or don't maintain them, disaster follows - brakes overheating, catching fire, trucks running away on steep downhills because the driver was to start at the top of the pass, etc. Unfortunately, human error is often a major culprit.

The air on a trailer is two fold, one line is to release the spring brakes, No air brakes on, the second line is for the running brakes which apply when the foot brakes of the prime mover are applied, when the hand brake is applied it releases the air from the spring brakes & locks the trailer.

Bazzer

It seems the company Rail World Inc had been cost cutting for some time, and this train was being operated by one engineer only, this and neglected maintenance issues no doubt contributed to the accident...The lack of rail cars with manual hand brakes set, seems to be the issue...One man operating a train this size for this distance is an accident waiting to happen....imo

..."Air brakes on the train are supplied with air from a compressor on each locomotive. When a locomotive is shut off, the compressor no longer supplies the brake system with air. An air brake pipe connects to each car and locomotive on the train. When air leaks from the various components, the air pressure drops. If the system is not recharged with air, the locomotive air brakes will become ineffective and provide no braking force. When the air brake control valves sense a drop in pressure in the brake pipe, they are designed to activate the brakes on each car. However, if the rate of leakage is slow and steady, the automatic brakes may not be applied as in the case of the Lac-Mégantic accident.^[38] The train had locomotives that could automatically restart the air-brake system in the event of a brake failure, provided that these locomotives were not shut down as they would be. Also, the TSB found that the “reset safety control” on the lead locomotive was not wired to set the entire train’s brakes in the event of an engine failure.^[39][40]

In addition to air brake systems, all locomotives and rail cars are equipped with at least one hand brake. This is a mechanical device that applies brake shoes to the wheels to prevent them from moving. The effectiveness of hand brakes depends on several factors, including their age, their maintained condition, their application in conjunction with air brakes, and the force exerted by the person applying the brake, which can vary widely. The TSB estimated that somewhere between 17 and 26 hand brakes would have been needed to secure the train. Which if there would have been a two-man crew the crew would have been able to perform a stabilization test, which is all air brakes released and ensuring just the hand brakes will hold the train. Since there was only a one-man crew this test was not possible.^[38]"...

^{https://en.wikipedia.org/wiki/Lac-M%C3%A9gantic_rail_disaster}

Bottom line:No air to brakes should mean brakes on,or loss of electrical signal to braking system should be brakes on.

This control logic would have prevented the tragedy,IMHO.

They have that safety feature, it wasn't hooked up...

Watch this.

The problem as I see it is that the trains are competing with the pipelines...when the trains get too expensive they build a pipeline, so the rail companies are forced to reduce costs to stay in business...

First to say, I haven't read any replies.

I had never thought of this - that trains and larger road vehicles used a pneumatic system for braking and controlling acceleration.

Looking on Wiki, I found this:

Advantages[edit]

Air brakes are used as an alternative to hydraulic brakes which are used on lighter vehicles such as automobiles. Hydraulic brakes use a liquid (hydraulic fluid) to transfer pressure from the brake pedal to the brake shoe to stop the vehicle. Air brakes have several advantages for large multitrailer vehicles:^[1]

• The supply of air is unlimited, so the brake system can never run out of its operating fluid, as hydraulic brakes can. Minor leaks do not result in brake failures.
• Air line couplings are easier to attach and detach than hydraulic lines eliminating the risk of air getting into hydraulic fluid since there is no hydraulic fluid. Air brake circuits on trailers can be easily attached and removed by operators with appropriate training.
• Air not only serves as a fluid for transmission of force, but also stores potential energy. So it can serve to control the force applied. Air brake systems include an air tank that stores sufficient energy to stop the vehicle if the compressor fails.
• Air brakes are effective even with considerable leakage, so an air brake system can be designed with sufficient "fail-safe" capacity to stop the vehicle safely even when leaking.

I think that, at the time of development, there was the added advantage of being able to produce and control less than atmospheric pressure (vacuum), so that's what they went for in the design.

Oh, and this on George Westinhouse is interesting:

https://en.wikipedia.org/wiki/George_Westinghouse#Air_brakes

I just haven't delved into how to do the LMGTFY yet

Railroads need to be able to move cars around either via switchers or in classification yards "hump" yards quite often. If would either be very time intensive with switchers or not work at all with hump yards to have cars that have their brakes on all the time.

A hump yard is a yard built with a hill or incline. Cars, one by one, are allowed to "coast" passed a reader/scale that figures out what car it is and where it's going and weighs it. As it's coasting down the hill, the proper switches are aligned to put the car onto the proper track, then retarders slow the car based on the weight.

Shawn

A simple 3 port electric solenoid valve, on the air line,as close to the brake cylinder as possible would fit the bill.

The operation of the brake would occur with no power to the solenoid,and would open a quick exhaust port on the brake cylinder line,while blocking the normal air supply.It would require a signal to energize the solenoid,which would allow the normal control of the brakes.

Since it would only require dumping a small amount of air from the cylinder,it would not require a long refill time.It could be refilled from the emergency reservoir,which could be topped off slowly while underway.

A manual bypass valve could be used on the hump,to allow release of brakes during hump operation.A valve position switch or (sensor;wireless or otherwise) on the manual bypass to signal the loco that all switches were in proper position before moving the train.

Why would this not work?

When I was a teenager, I worked at the local farm supply co-op. In the fertilizer dept. we received potash via rail cars. The railroad (It was Soo-Line at that time) would drop off about 6 or 8 cars. There was a slight incline (hardly enough to see) on the spur line. To unload cars we would release the hand brake and let the car roll until the hopper discharge was over the conveyor. If we let it roll too for, we had to move it back a few inches at a time with a rail car jack.

I don't think this would be possible with the system you describe. I'm sure a lot of smaller customers would have the same issue.

I think overall our railroad system has a very good safety record.

Any system is only as good as the people who operate it.

Rail cars can weigh up to 300K pounds each. Below is a typical brake shoe. That's a lot of inertia to overcome with mechanical brakes.

You're right. single cars are moved around all the time.

Usually, the first car in the string being built actually stops the car in the hump yard or on a siding. Air lines are connected when cars are switched on flat sidings by the line locomotive, but are broken when the car is freed by the engine which can be a hundred feet to the front car in the line. Makes quite a bang when they connect.

We're back to a lack of proper funding/oversight as the culprit in these line accidents.

And we all know why that is.

This is how I understand the disaster :

A. The train had 7 brakes applied when it was sitting on the tracks.

B. If the engine has been idling normally, then the supplied air pressure would have been sufficient to hold the train stationary.

C. The trains engine caught fire, improperly trained volunteer firefighters we're sent in to extinguish the fire.

D. Firefighters we're told to turn off the engines fuel supply valve, turning off the valve shut down the engine.

E. When the fuel supply valve was turned off, there was no fuel available to support the fire.

F. When the engine turned off, the air compressor that supplies pressure to the brake system stopped operating.

Some points to consider :

A. Why did firefighters, who were not trained to fight railway fires dispatched to the scene.

B. Did the person who advised the firefighters to shut off the engines fuel supply know that a loss of brake control could result.

C. Why was the Engineer notified after the crash happened and not when the engine fire was in progress.

D. Why did the firemen leave the scene after the engine fire was put out and the train and it's cars were unattended.

E. If the rail authority knew the engine was disabled, why didn't they bring in a backup engine to supply air ( pressure ) to the train.

In this instance, trying to figure out who to blame will be difficult if not impossible. The person or persons responsible for creating the standard operating procedures in dealing with an emergency of this type may or may not still be associated with the company.

Usually it's the low man on the totem pole who will get the blame, those in upper level control can say that those person or persons failed to follow specific guidelines.

If the railway company is indeed bankrupt, then where will monies come from to satisfy liability claims.

The phrase, " That's an accident waiting to happen " comes to mind, this statement is usually remarked by a junior employee, who often is rebuffed by senior level associates, when the former continues with that type of digress, he or she is generally discharged for being a " Trouble Maker.

<...air is required to apply the brakes...> Not in the UK:

https://en.wikipedia.org/wiki/Regulation_of_Railways_Act_1889

The failsafe principle is there in braking systems in order for all parts of a train that has broken into several pieces to pull up without one or more of those pieces running away out of control, as happened at Armagh in 1889, with the loss of around 80 lives.

Any source of stored energy in the braking systems in the individual vehicles such as compressed air will dwindle over time. There is no substitute for the train crew applying a number of parking brakes to stationary rolling stock before the locomotive is uncoupled from them. One might reasonably query whether the number of parking brakes applied, and how completely they were applied, was sufficient to prevent a run-away, which is what appears to have happened at Lac Megantic.

I asked the same question shortly after the Lac Magnetic incident happened. Got some informative responses.

http://cr4.globalspec.com/thread/85428

See also the wikipedia link in that thread on Railway Air Brakes. It details the differences between semi and railway air brake systems.

I have just spoken to a friend who drives Coal trains here in Australia.

He tells me that this has been an ongoing concern when air pressure becomes too low to maintain the brakes. The newest cars that they use here now have a pin that drops in to keep the brake shoes in hard contact with the drums whenever the "train line" (that's the name of the air line that runs the length of the train) has insufficient air to keep the air tanks charged, or when the train line is vented to atmosphere during an emergency stop. The pins do not retract again until air pressure has been restored.

The trains use Electronically Controlled Pneumatic brakes (ECP) where the train line remains charged at all times except during an emergency stop when the engineer can vent it straight to atmosphere and thus cause all brakes to apply - the older style use venting of the train line as the normal way of applying the brakes, but this can leave the tanks partially or totally depleted of air for some time after operation. The electronics can also allow the rearmost cars to be braked first to prevent the bunch-up that otherwise occurs - he says this gives a far more comfortable ride than the older system.

Another advantage of this is that manual parking brakes do not need to be applied when the train line is disconnected when removing cars etc. as the pins would then be locking the brakes in place, although he said that they still do that as well - apparently 10% of cars are required to have the parking brakes applied whenever the loco is vacated.

At Last! A system designed with safety as the starting point!

A simple effective fail safe system.

Which brings to mind:How do the truck-trains that are famous in Australia apply their brakes?

There must be some type of ECP to sequence the brakes starting from the rear to prevent pile-up or fishtailing.

Perhaps they use a similar system?

OK, a trick question:Where is the clutch on a train?

They do have a clutch,but not what one would usually think of as such.

I have no idea re the road trains, but as they are solid connections between individual trailers, and generally only up to a maximum of 5 trailers (that i have seen anyway), they probably don't require sequencing, but these braking systems could likely be adjusted to provided more stopping power to the rear trailers just like you can with electric brakes on your own trailer, as opposed to actual sequencing.

As for the clutch in a train loco, most are diesel electric - diesel motors running generators to provide power to electric motors to power the wheels - as this method provides full torque at zero RPM and better control. Back off on the accelerator control and the electric motor ceases its output, thus requiring no clutch. I haven't discussed this in detail with my driver friend, but they may employ some form of dynamic braking as well when decelerating.

Ok,the answer to the trick question:

A clutch,by definition, applies the load slowly to prevent overloading the drive train or traction ability.

This is accomplished by the hysteresis in the couplings between cars.

As the train begins to move,,the load is applied gradually as the slack comes out of the couplings.(told ya it was a trick question).

I think due to the length of a train which could be a mile long, loss of air down the line could apply the brakes to a single car which would then be a drag on the entire train. That could cause a derailment or a fire . Imagine a tank car carrying flammable cargo and it's brakes locked up. It is probably best to apply brakes/air as needed to stop a train than to have a car stop automatically. Trailers only have to deal with 40 or 50 feet, not a mile of brakes.

Each car or carriage should have it's own storage tank & the air from the engine is a signal to tell a brake valve to open and apply the brakes, if you look there are two lines at least coming from the engine one is to supply the air the other to act as the signal, I don't know for sure but I would think that in this day and age that because trains are so long that carriages would have there own compressors driven from the axels of the carriage, these would keep the air tanks topped up and the signal would release the air to the brakes.

Bazzer

Hose is cheaper than compressors for each car.

Retrofitting each car with a gearbox and compressor would be a massive expense and maintenance headache.

Not really, just a compressor belt driven from the axle no gearbox needed, can you imagine how long the delay would be on a train a mile long, then to have to

re-pressurise it again.

Bazzer

In 2016 there were:

414,000 tank

137,000 hopper

218,000 gondola

198,000 flat

539,000 covered hopper

and

109,000 box

railroad cars in the USA for a total of 1,615,000, not including powered cars as it is assumed they would have compressors already.

That's a lot of belts and compressors.

Each car does have its own storage tank which is topped up from the locomotive compressor via the main air pipe (called the "train line"). The second pipe to which you refer is the one that controls the brakes - not by supplying air, but by denying it. The reduction of air pressure in that line - caused by the engineer venting it to atmosphere - produces a differential between the pressures in the storage tank and the control line thus allowing the brakes to activate via a device called the "triple valve.

Many trains now use electronic pneumatic braking systems - ECP - which uses an electrical signal sent down auxiliary cabling, or even via radio control to activate the brakes (these ones have wheel generators on each car).

The FMG railway in Australia - reputed to operate the longest and heaviest trains in the world - uses a 200V DC ECP wired system

682 "wagons" is rather long.

I saw this on a You Tube site, just now.

On a mile long train I wonder what the delay is when re-pressurising the signal line ?

Bazzer

Look up a Westinghouse AB brake valve. Because of the distance air would have to travel in a trin compared to a truck, working air pressure is built up then small pressure changes operate the brakes. -- JHF