Standing train can roll when air lost?

If ALL the air leaks off, including the air in the brake cylinders, then there are no brakes. That will happen on a train left standing for a long time.

 

That's why railroad cars have hand brakes.

I realize that railroad air brake design and operation can be confusing, so try this basic explanation:

 

1) Each RR car has a two section/portion air reservoir. The one portion is the service portion and the other is the emergency portion.

 

2) The main brake pipe/train line charges each and every car in the whole train, with say 80psi air pressure, which charges BOTH portions of each cars reservoir.

 

3) To then apply the brakes on avery car, some air is "drawn down" on the train line. The control valve on each and every car senses the brake pipe reduction, and an internal valve supplies the amount of air pressure reduction, from the service portion of the reservoir, and supplies that air into the brake cylinders which force the brake shoes against the wheels.

 

4) In order to release the train brakes, the train line is re-charged back to the original 80psi, the control valve in each car senses THAT, and releases the air pressure in the brake cylinders and subsequently re-charges the service portion of the reservoir back to the original 80psi.

 

 

So, in brief conclusion once a train is completely completely charged, it takes a REDUCTION of air pressure to apply the brakes. That way, it is essentially a fail-safe system, i.e. if the train brakes in two and the train line air is lost, the brakes apply in emergency from the air pressure stored in each and every reservoir on each and every car. However, when total air pressure is eventually lost on a car, or a whole train (everything leaked to atmosphere), then there are no longer ANY BRAKES on any car or the whole train, except of course for the manual/mechanical hand brake.

 

Hope this helps a bit. 

Here you go, How Train Air Brakes Work.

 

Basically, it's not a fail-safe system.

 

Rich, thanks for your railroad expertise and sharing it. In reading the link referenced by Terry, only some car brakes were set allowing the cars to roll, is it railroad policy for every car brake to be set on an unattended string of cars? If so, seems like that would require quite a bit of time to accomplish depending, of course, on the number of cars.

 

In the case of the Lac Megantic disaster ..... is it true that the departing engineer was required to set only an estimated number of car brakes, and then test the situation by releasing the air brakes .... and see if the train moved? If the train did move, he would set more car brakes.

 

But, he failed to properly perform this test? And, the train rolled as the air brakes faded?

Rich, John and "Hot," many thanks for the info and link. Definitely more complex than I realized and not so "fail-safe" as I thought either.

 Yes . I know of a set of empty gondolas  that had set quite a while in a middle track,obviously the air had all depleted out of the air system.

 Well here comes along a few juveniles that knock the handbrakes off.Out go the cars on what looks like pretty level track,onto the mainline !

 

 Fortunately the code line caught the intrusion and put up red signals in the block before an eastbound found them.

 

 

That is an oversimplification and not the whole story about what happened, which really doesn't need to be dredged up again.

 

I know that is not the whole story of what happened that day .... the problems they were having with that particular engine, the fire, etc.   

 

But, I had thought it all boiled down to that. Do I misunderstand something? I'll read up on it.

 

An oft-used standard for setting hand brakes is 10%. Got a 60 car train? If you're going to leave it unattended somewhere, you have set AT LEAST 6 hand brakes. If the train is to be spotted on a grade, many more hand brakes may have to be set to hold the train.

 

Operating rules require that when tieing down a train, the crew must set the hand brakes, then release all the air brakes (the train brakes and the independent brake on the locomotive) and confirm that the hand brakes actually will hold the train.

Thanks again Rich. I got it. Set the prescribed number of hand brakes or more then test by removing air from the equation.

I have a question, watching a hump yard in Colton CA. a few years back the cars were pushed up a hump, a yard worker released the coupler bar and the car was sent down the hump, when the car uncoupled the air hose would break off.

1.  the car is rolling no breaks on so I am taking it somewhere the air was released at somepoint so it could move.

2 who does it and when?

 

They wish! I would say few yards have the space between tracks to ride anything. They WALK, inspect and bleed.

 You must be thinking of commercial truck air brakes. Truck air brakes are actually applied by pressure from a sping inside a "brake chamber".

 

The air realeases the brakes and compresses the spring. When a tractor trailer loses all air pressure the brakes come full on.

In a good example of a rule written  to assign blame when hand brakes didn't hold, the NORAC rule used to say that a "sufficient number of hand brakes" must be applied to standing cars. The test? If it rolls away, it wasn't sufficient! You lose. The road specific timetable that I worked under specified 50% of cars hand brakes must be applied, but our trains were not very long.  I do know of a conductor on a major main line that  once set twenty hand brakes a freight train was stranded on a 1.5% grade before going off duty. The fresh crew wasn't very pleased, but their train was still where he left it hours before. Safety First is often hard work.         

Thanks Hot Water, this is very good tread, it answered a lot of questions.

Thanks guys!

 

 

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Ok, so being somewhat of a newbie, I have to ask: Why aren't train brakes done this way? Seems like it would be (more) failsafe.

They are! When air is lost in the brake pipe, the brakes go into "emergency" which is a full-on application of the air.

 

That spring applying the truck brakes is the equivalent of the emergency application of air on a train brake.

At West Colton, the only people walking tracks are brakeman. The Carmen drive their jeeps, gators, 4 wheelers, etc etc between every track in the yard.

 

In the past 2 years, all the receiving tracks were completely torn out and replaced with concrete ties, welded rail, and new asphalt between every track. The departure yard is next.

 

Even in the BNSF Barstow yard, the herder/bleeder drives a utility vehicle between tracks with a 3' rod in hand to bleed the cars off. They used to walk every track.

So how in the wide wide world of sports are the cars getting a decent inspection with a guy riding by on an ATV? That reeks of unprofessionalism!

Remember, they aren't inspecting freight cars with plain bearing journals and car oil anymore.

No, but, also don't forget that there are many other things to inspect! Very little can be seen with only a roll-by inspection. So, the question is, where are the cars getting a proper inspection?