I’ve read references that leaving a train secured by hand brakes with the automatic brake released was normal practice on some or parts of Canadian railroads. In theory, with a sufficient number of hand brakes applied the train won’t move. Even railroads that require air brakes to be applied to unattended trains require a sufficient number of hand brakes applied. After applying them, they are tested to make sure they hold. If they don’t, more are applied. (Our instructions, depending on locations, may have minimum numbers required. It does not relieve doing the securement test. If the minimum number doesn’t hold, tie more hand brakes.) Our test is to release both automatic and independent brakes and check for movement. After the securement has been deemed satisfactory, and it might take a few minutes to allow slack to fully adjust, the automatic and independent brakes are reapplied. The assertion that allowing air brakes to be applied leads to less hand brakes being set (IMO) is pure BS.
Without re-reading everything about this incident, a number of practices that had been considered normal and appropriate were used. I believe at least one procedure was done incorrectly from what I’ve read. That is, going by memory, doing the push/pull securement test with the independent brake set which gave a false sense of securement. Had the independent not been applied during the push/pull test, it may have allowed movement showing that more hand brakes were needed. Allowing hand brakes on the engines to be counted toward total train securement (which leads to less brakes being set on cars) may not have been wise. I must say though that some places allow engine hand brakes (in the lead consist) to count, other places don’t even though the locomotive’s hand brakes must still be applied.
I’m not sure that I can agree with the premise that the railroad, or it’s empl
regarding your reference to leaking off of the trainline without setting the car brakes, I would like to consider just that possibilty alone before we consider how the ten-second procedure might have affected that.
I asked that same question back in earlier threads about this. That is, how does the trainline leak down without setting the air and pressurizing all the brake cylinders? Somebody answered the question, and I recall that one or more others reaffirmed the answer. I have never heard of this before, so I do not know if it is true, but I find it hard to believe.
In any case, the answer given was that because the trainline reduction was so gradual, it was able to leak to zero pressure without the control valves sensing that fact. This was said to be a well-known possibility. So the train ran away with fully charged reservoirs, and no charge in the trainline or the brake cylinders. I still don’t understand how that is possible. Regardless of how slow the pressure drop is, eventually it results in a big pressure differential between the reservoir and the trainline. How can the valve not sense that big differenc
With a running locomotive, it is possible to completely open the brake line to the atmosphere without applying the brakes. I’ve done it.
This is, of course, due to the pressure maintaining feature in modern locomotives. The backup hose dump valve was opened slowly enough that the locomotive was able to compensate and the brakes did not apply.
So the possibility of the trainline bleeding off slowly enough that the brakes don’t apply is definitely within reason.
A normal “first service” (6 lb reduction) occurs relatively quickly, but not so quickly as to initiate an emergency application.
OTOH, normal acceptable leakage on a train is between three and five pounds per minute. With a relatively tight train the leakage might be as low as one pound per minute (or less).
A half pound of leakage per minute would mean the train line would take three hours to go from 90PSI to zero.
We are told that leakage caused the independent brake to release. Was that leakage also reducing pressure in the trainline at the same rate? Where would the leakage be located that would cause the independent brake to release?
Air Brakes 101. The independent brake is completely separate from the automatic brake. They are linked (if the automatic is applied, the independent also applies) but can, and do, operate separately. The independent can be applied, as well as released (actuated/bailed off), without affecting what’s going on with the train brakes.
The leakage that would cause the independent brakes to release would occur somewhere on the locomotive consist. There are many possibilities.
I generally understand that separation between independent and automatic, but not all the details. Could leakage that caused the independent to release, have occurred without involving the train line charge and lowering the pressure of the trainline?
I’ve got quite a bit to say, so will spread this over a few posts and add some additional info for those unfamiliar with railway air brakes.
Before the Lac-Megantic disaster the rules and regulations around train securement were much looser, apart from a “sufficient number” of handbrakes being applied to cuts of cars left off air the railroads were quite free to make their own rules, and monitoring/enforcement by Transport Canada was rare.
I can’t speak for the regionals or shortlines, but CN and CP had very different rules for securing trains when the locomotives were left attached with air brakes cut in.
CN required a full service application of the automatic brake (air brakes on cars), full application of the independent brake (air brakes on locomotives) and one handbrake on the lead locomotive, but
CN did not allow the locomotive handbrakes to be counted towards the total required to secure a train, and also required that handbrakes be tested with a push or pull test (depending on the direction of the grade). By default this required releasing the independent brake at least enough to allow the locomotive consist to move itself.
I am not sure what CP or MMA’s procedures were for testing handbrakes, but I believe they also required some sort of push/pull test.
I’m pretty sure I am not that forum member, but I do know why the air brakes behaved the way they did at Lac-Megantic, and I have experienced it myself at work.
In the TSB report the air brake manufacturer (WABCO or NYAB presumably) stated that a reduction rate of at least 3 PSI per minute was required to ensure application of the air brakes on a car. Understanding this requires a bit more of a detailed explanation of how the car control valve works internally.
The air brake application depends on the difference in air pressures on two sides of a slide valve, the reservoir and the brake pipe. The two sides are also connected by a small (3/32 of an inch in diameter) passage through which air flows to charge the car’s reservoir. The small size of this passage is also why it takes so long (~7 minutes) to fully charge a car.
Let’s start with the car fully charged, both the reservoir and the brake pipe are at 95 PSI (the pressure MMA was running at). The Engineer moving the brake valve in the cab reduces the brake pipe pressure fairly quickly, so now at the car the brake pipe is at a lower pressure than the reservoir. This difference in pressure forces the slide valve over, which blocks the 3/32’’ passage while also exposing the pipe to the car’s brake cylinder. When the Engineer moves the brake valve to release this process is reversed, allowing the car’s reservoir to be recharged from the brake pipe.
Also, the 3 PSI per minute reduction rate is only required to set the brakes intitially. Once this has happened any additional reduction, no matter how slow, will result in a stronger brake application. This is why the Canadian rules now require at least a minimum application of the automatic brake to secure unattended trains.
The independent and automatic brake systems are connected, and both are connected to the locomotive’s main reservoir. All also suffer from myriad small leaks as one would expect from a air system out in the real world. A leak in one system, combined with a lack of MR air pressure to compensate for it will result in the slow bleeding off of both systems.
I also realize that I have given a very simplistic explanation of the air brake system, and have left out the emergency reservoir and other portions like quick service, quick charge, retainers, load/empty features, and pressure maintaining etc. Just trying to keep this from getting out of hand.
Thanks for that explanation. That is basically what was explained in earlier threads (although not as well detailed as how you have explained it here) when this question came up, as I refered to when repsonding to Jeff above by saying this:
SD70M-2Dude
In the TSB report the air brake manufacturer (WABCO or NYAB presumably) stated that a reduction of at least 3 PSI per minute was required to ensure application of the air brakes on a car. Understanding this requires a bit more of a detailed explanation of how the car control valve works internally. The air brake application depends on the difference in air pressures on two sides of a slide valve, the reservoir and the brake pipe. The two sides are also connected by a small (3/32 of an inch in diameter) passage through which air flows to charge the car’s reservoir. The small size of this passage is also why it takes so long (~7 minutes) to fully charge a car. Let’s start with the car fully charged, both the reservoir and the brake pipe are at 95 PSI (the pressure MMA was running at). The Engineer moving the brake valve in the cab reduces the brake pipe pressure fairly quickly, so now at the car the brake pipe is at a lower pressure than the reservoir. This difference in pressure forces the slide valve over, which blocks the 3/32’’ passage while also exposing the pipe to the car’s brake cylinder. When the Engineer moves the brake valve to release this process is reversed, allowing the car’s reservoir to be recharged from the brake pipe. But, and here’s the kicker (pun intended), if the brake pipe pressure is reduced at a very slow rate then air will simply flow out of the reservoir through the 3/32’’ passage back into the brake pipe, and the pressure stays approximately the same on both sides of the slide valve. As a result the valve does not move over, no air is sent to the brake cylinder and the car’s air brake stays released.
Thanks for that explanation. That is basically what was explained in earlier threads (although not as well detailed as how you have explained it here) when this question came up, as I
So, as I understand this, the slow leakage that reduced the pressure in the locomotive independent brake cylinders would have, at the same time, reduced the pressure in the main reservoir, the trainline, and all of the car reservoirs. As this leakage continued, it would have exhausted all the air pressure in all four of these elements. And because the leakage was so slow, there was no valve movement on each car that would have diverted air from the car reservoirs into the car brake cylinders, so they remained fully released. Then when the falling pressure was low enough, the locomotive independent brake cylinders released, and the train rolled away.
Main reservoir on locomotive feeds brake pipe and locomotive brake cylinder. Engine shuts down. Compressor stops pumping air. Main reservoir pressure starts to drop. As it drops, so does the brake pipe and independent brake pressure.
I was treated to this last trip when the DP shut down and wouldn’t restart. I watched, as we waited for a mech. dept guy to come out, the DP’s main reservoir, equalizing reservoir (which “controls” the brake pipe) and independent brake pressure leak away. All three stayed within one to two psi as the air leaked off. In this case, it didn’t affect the brake pipe because the DP had cut it’s brake valve out automatically.
Yes you are “Articulate” and so is Jeff. I thank both of you for enlightening me and I suspect many others. The 3/8’ orifice was new to me and your explanation very good. Thanks to both you and Jeff.
PS Jeff. I presume you can see the DP units pressures from the front unit on a monitor. It gives you all the data? IE, you (or your conductor) didn’t have to walk the train>
Don’t know UP Rules. On CSX - train in emergency - with HAZMAT - even if air restores immediately must be walked to verify that the HAZMAT is still on the rail.
If the air doen’t immediatly restore on ANY train, it must be walked.
Conductors frequently reported finding ‘stuck vent valves’ in situations where the air didn’t restore and they cut the brakes out on the offending car.
Repeating for the umpteenth time, whether or not the engines were running would make NO difference if the train were properly secured. If the train were properly secured you could have shut down the engines or even turned the angle cock and disconnected the engines and it would not have made a difference. The train would have stayed put IF it was properly secured. The questions about the engines are a waste of time and electrons.
Those are the more relevant questions.
How many handbrakes were required by calculation? How many handbrakes were required by rule How many handbrakes did he think he needed to apply? How many did he apply? If there is a discrepancy between any of those numbers, why?
I realize that it makes no difference whether the engine was shut down in the terms you are describing. I am fully aware of the fact that air brake must not play any part in the securement. But I asked the question for a different reason, which I think is pertinent to the overall question of negligence, intent, etc.
The reason I ask whether the engineer was told that the engine had been shut down is that he knew that the running engine was needed to maintain the set inedpenent brakes which he was relying on the hold the train. So even though it was wrong to secure the train that way, that is the way the engineer securred it. I assume he believed that it was okay to secure relying on the independent brakes.
So given that background, I cannot believe that the news that the one running engine was shut down would not ring a very loud bell in the mind of the engineer. And if engineer experienced that realization that th
Euclid
If he answered yes to that question, I would like to hear him state whether he was told that the faulty engine had been shut down by the fire department, as I understand that he had conversations about the fire with his supervisor(s)
What difference does it make?
Repeating for the umpteenth time, whether or not the engines were running would make NO difference if the train were properly secured. If the train were properly secured you could have shut down the engines or even turned the angle cock and disconnected the engines and it would not have made a difference. The train would have stayed put IF it was properly secured. The questions about the engines are a waste of time and electrons.
Dave,
I realize that it makes no difference whether the engine was shut down in the terms you are describing. I am fully aware of the fact that air brake must not play any part in the securement. But I asked the question for a different reason, which I think is pertinent to the overall question of negligence, intent, etc.
The reason I ask whether the engineer was told that the engine had been shut down is that he knew that the running engine was needed to maintain the set inedpenent brakes which he was relying on the hold the train. So even though it was wrong to secure the train that way, that is the way the engineer securred it. I assume he believed that it was okay to secure relying on the independent brakes.
So given that background, I cannot believe that the news that the one running engine was shut down would not ring a very loud bell in the mind of the engineer.