Deggesty Yes, Congress should be apprised of the fact that their equation is incomplete, and be given an F.
Yes, Congress should be apprised of the fact that their equation is incomplete, and be given an F.
Congress is the professor giving the grade. The railroad industry is the student.
If the train is in "Emergency" (as is now dictated by Transport Canada) as stated previously, it will hold for days, not minutes or hours. Setting the handbrakes is a non-vital "row of nails" that will assist in holding the train while the brakes are being recharged when it's time to leave. At that time the locomotive independent brakes can also provide the holding function at that time.
Many years ago, i managed a program to automate a freight train hauling 10,000 trailing tons of ore down a perilous grade in Wyoming. It wasn't easy but we never lost control. The car brakes were ABDW; all of the automation was confiined the locomotive.
Jerry Pier
What is the maximum allowable leakage rate (X decrease in psi in Y minutes, etc.) in the trainline ?
If the trainline did leak at such a rate, how long would it be until the air brakes 'bleed off' and are released ?
Anybody know what the maximum retarding force for a handbrake is - or a set of 8 of them on a typical freight car ? My understanding is that the wheels will turn and slide past the brakeshoe rather than lock-up and slide on the rail, hence the brakeshoe friction is the governing factor in how much resistance a car with fully applied handbrakes can provide against a train that wants to roll downhill.
Note that even if a few handbrakes or trainline air brakes had been applied, after a few miles at speeds > 25 or 35 MPH the brakeshoes will overheat. Then, a phenomenon known as "brake shoe friction fade" will start to occur, and the braking resistance will decrease, causing the train to go even faster - a descending spiral of cause-and-effect that usually ends in disaster. The Canadian TSB is familiar with this scenario - see its "Railway Investigation Report R06V0136" on the CN/ British Columbia runaway locomotive and loaded center-beam flatcar in the Fraser River Canyon near Kelly Lake and Lillooet on 29 June 2006 at:
http://www.tsb.gc.ca/eng/rapports-reports/rail/2006/r06v0136/r06v0136.asp
- Paul North.
Paul_D_North_Jr What is the maximum allowable leakage rate (X decrease in psi in Y minutes, etc.) in the trainline ? If the trainline did leak at such a rate, how long would it be until the air brakes 'bleed off' and are released ?
Paul,
The leakage that Jerry refers to is not from the trainline in the normal sense of leakage from a pressurized trainline. It is leakage from the pressurized brake cylinder and connected reservoir on each car individually with some cars leaking down faster than others.
I have never understood where this leakage escapes to atmosphere. Is it through the cylinder past the piston, or through the valve? If it is through the valve, does it exit the valve through the exhaust vent, through the bleed valve, through the open trainline, or a combination of those routes? Maybe somebody could explain this.
First let's clarify some terms. The air pipe that leads through the train is called the "brake pipe". "Train line" refers to electrical connections sending power from one passenger car to the others.
A leakage test is performed on the brake pipe when the train is made up at its "initial terminal". The specification is that the brake pipe leak no more that 5 psi/minute a minute after a brake pipe reduction. Where does that air go?
1) The brake pipe charges reservoirs in the cars and any car not fully charged will drain the brake pipe.
2) There is a glad hand connection between cars and that may leak.
3) Charged air is heated by compression and cooled by expansion. As tanks charge they warm up and temporarily raise the pressure. As that heat dissipates, the pressure in the tank drops (without any loss of molecules)
4) Small leaks throughout the piping, valves and tanks of the air system. Though normally the air systems of cars are tight and will hold air for days. Small amounts of dust and dirt may prevent automatic valves from closing completely and that is a common leakage source.
The brake cylinder has a rubber lined piston that is fairly close to air tight. When the brakes are applied some small amount of air may leak past that rubber gasket. That leakage and the leakage of the brake pipe will eventually drain the air system to zero psig. Even if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days.
The Brake Pipe on the Quebec train had 171 possible leakage points, ie; at each hose coupling. Leaks are worse at low temperatures but you can walk a standing train at any time and probably hear air hissing out at one or more gladhands. Pressure maintaining takes care of this as long as Brake Valve handle is in the right position and the compressor is providing air. When the locomotive is shut down, you are at the mercy of the main reservoir volume which is finite.
With brakes in Emergency, Brake pipe pressure is zero, leaving the only point of leakage the brake cylinder line. The pipe itself is extra heavy so breakage or corrosion is pretty much out of the picture. (The old expression in braking and signalling is that, because of unction, you can't make it vital [fail safe], make it hell for strong..)This leaves two point of possible leakage, The flange fitting to the Pipe Bracket and the Brake Cylinder cup. The flange fitting is sealed with a square cross section ring seal contained in a controlled compression groove, ie; flange tigtens metal to metal. Gasket material is a synthetic specifically developed for service at all temperatures so while leakage can occur it is relatively rare and tends to be minor. The brake cylinder cup is also designed for the specific service. Leakage can occur with brake cylinder wear or cup degradation due to lack of lubrication or age. In any case such a leak will tend to be slow, assuring braking for for days rather than hours or minutes.
Iron brake shoes would melt under severe braking conditions. Todays non-metallic shoes are compounded for specific services and are much less likly to "flame out"
Jerry PierThe Brake Pipe on the Quebec train had 171 possible leakage points, ie; at each hose coupling. Leaks are worse at low temperatures but you can walk a standing train at any time and probably hear air hissing out at one or more gladhands. Pressure maintaining takes care of this as long as Brake Valve handle is in the right position and the compressor is providing air. When the locomotive is shut down, you are at the mercy of the main reservoir volume which is finite.
Jerry,
Thanks for your explanation of the cylinder leak down. As I understand it, you are ruling out that kind of leakage playing a role in the MM&A runaway because sufficient leak-down would have taken a lot longer than just the hour or so that it took for the train to start rolling.
But I have some questions about the part that I have quoted from you above. I understand the issue of trainline/brake pipe/gladhand leakage, but how exactly could that have played a role in the runaway?
As I understand it, the trainline was at reduced pressure with brakes set. If there was trainline leakage, and if the engine shut down, the trainline might have leaked down to zero. But so what? Would you not still have air pressurizing all the brake cylinders of the cars?
One or more others have given the explanation that the only braking that would have been reduced or eliminated due to leakage if the compressor shut down was confined to the independent brakes.
petitnjEven if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days.
Yes that is the part that I am referring to in my reply to Jerry above. My conclusion overall is that the shut down of the one running locomotive and resultant loss of the compressor could not have resulted in the release of the air brakes on the train. Is that correct?
I understand that the loss of the compressor could have resulted in the release of the independent brakes. I have no idea how little time that could take. However, even if the independent brakes released, I assume that the train brakes would still have prevented the train from rolling.
Bucyrus petitnjEven if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days. Yes that is the part that I am referring to in my reply to Jerry above. My conclusion overall is that the shut down of the one running locomotive and resultant loss of the compressor could not have resulted in the release of the air brakes on the train. Is that correct? I understand that the loss of the compressor could have resulted in the release of the independent brakes. I have no idea how little time that could take. However, even if the independent brakes released, I assume that the train brakes would still have prevented the train from rolling.
Unless there was leakage from a car or cars into the trainline that increased the trainline pressure 1 1/2 to 2 pounds, which would have signalled the brake valves on all cars to release.
Never too old to have a happy childhood!
BaltACD Bucyrus petitnjEven if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days. Yes that is the part that I am referring to in my reply to Jerry above. My conclusion overall is that the shut down of the one running locomotive and resultant loss of the compressor could not have resulted in the release of the air brakes on the train. Is that correct? Unless there was leakage from a car or cars into the trainline that increased the trainline pressure 1 1/2 to 2 pounds, which would have signalled the brake valves on all cars to release.
Bucyrus petitnjEven if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days. Yes that is the part that I am referring to in my reply to Jerry above. My conclusion overall is that the shut down of the one running locomotive and resultant loss of the compressor could not have resulted in the release of the air brakes on the train. Is that correct?
Today CP and CN are both in CYA Mode running notch 8. Story and video are both very Interesting.
http://www.ctvnews.ca/business/cp-rail-cn-reviewing-safety-procedures-after-derailment-in-lac-megantic-1.1372546
Bruce
So shovel the coal, let this rattler roll.
"A Train is a Place Going Somewhere" CP Rail Public Timetable
"O. S. Irricana"
. . . __ . ______
Bucyrus BaltACD Bucyrus petitnjEven if the brake pipe leaks to zero, the car's air reservoirs and cylinders will hold pressure for hours or maybe days. Yes that is the part that I am referring to in my reply to Jerry above. My conclusion overall is that the shut down of the one running locomotive and resultant loss of the compressor could not have resulted in the release of the air brakes on the train. Is that correct? Unless there was leakage from a car or cars into the trainline that increased the trainline pressure 1 1/2 to 2 pounds, which would have signalled the brake valves on all cars to release. But several people here have said that the pressure maintaining feature would not permit the trainline pressure to increase even if there were leakage into it.
With the engine shut down - there is no pressure maintaining feature active.
I thought there were at least a couple of engineers who insisted that shutting down the engine could not have caused a brake release.
So it sounds like the trainline was at a reduced pressure to have set the brakes; they shut down the engine; a little leakage from one or more car reservoirs leaked into the trainline; and slightly raised its pressre; that triggerd a full release of all car brakes, and away went the train.
What about the independent brakes? Would the full release of the train brakes also release the independent brakes?
With the engines shut down, if anyone of the cars had a leak in the auxiliary reservoir, that reservoir pressure will drop below brake pipe pressure, when it gets about 1 1/2 to 2 pounds below brake pipe the control valve will sense a rise in brake pipe and cause the emergency reservoir to dump a small amount of air into the brake pipe to rapidly propagate a brake release, the next car in line sense's the rise in pipe pressure and releases its brakes. If this defective car is in the middle of the train the signal to release is propagated in two directions
Bucyrus I thought there were at least a couple of engineers who insisted that shutting down the engine could not have caused a brake release. So it sounds like the trainline was at a reduced pressure to have set the brakes; they shut down the engine; a little leakage from one or more car reservoirs leaked into the trainline; and slightly raised its pressre; that triggerd a full release of all car brakes, and away went the train. What about the independent brakes? Would the full release of the train brakes also release the independent brakes?
If by independent brake you are refering to the engines independent system - that would not release because the train brakes released. With the engine shut down, the independent locomotive brakes can leak off because of leakage in thier own system,
If the train is on a grade and the cars are not properly secured by effective hand brakes and the air brakes are released for whatever reason, the train can roll down the grade - it can pull a locomotive consist with their brakes applied if the train is of sufficient weight and the grade is sufficiently steep. Having brakes applied on the engine consist alone is no guarantee that a train on a grade will remain in place if the brakes become released on the train.
Properly securing a train or a cut of cars is one of the cardinal responsibilities of employees in train and engine service - on my carrier failure to do it has become a firing offence (and has been from before the Canadian incident).
BaltACD If by independent brake you are refering to the engines independent system - that would not release because the train brakes released. With the engine shut down, the independent locomotive brakes can leak off because of leakage in thier own system, If the train is on a grade and the cars are not properly secured by effective hand brakes and the air brakes are released for whatever reason, the train can roll down the grade - it can pull a locomotive consist with their brakes applied if the train is of sufficient weight and the grade is sufficiently steep. Having brakes applied on the engine consist alone is no guarantee that a train on a grade will remain in place if the brakes become released on the train. Properly securing a train or a cut of cars is one of the cardinal responsibilities of employees in train and engine service - on my carrier failure to do it has become a firing offence (and has been from before the Canadian incident).
So the independent brakes might have leaked off and fully released or partly released; or they may not have leaked enough to release at al. But even if fully applied, the train could have still shoved the engines down the hill if the train brakes released.
I would think they have gotten some pertinent information off of the event recorder by now. I wonder when they are going to tell us what they found.
Bucyrus I would think they have gotten some pertinent information off of the event recorder by now. I wonder when they are going to tell us what they found.
If the Canadians operate anything like the US transportation investigative bodies - 6 months to a year for a final report. In addition to reading the event recorder - they will perform a number of tests on the various scenarios that were identified by their questioning of the parties involved in the incident. They will also document the brake conditions that were discernable from the wreckage as well as what of the cars and equipment that wasn't wrecked. Track notes and conditions will also be documented. Rest, toxicology and medical history of personel will be measured and documented.
The Independent Brake is a straight-air brake that connects to the locomotive brake cylinders via a double check valve. As the name implies, it is separate from the automatic brake system and must be applied and released separately.
The Event Recorder readings should be of great interest. (Was there an Event Recorder?). Since the cause of the air brake release is not obvious, it may provide a clue. I'm interested in what the firemen might have done inadvertently or by mistake in the process of shutting the engine down. Since I believe the Brake Valve handle was not removed by the engineman, it could have been moved accidentally, sending a release pulse through the brake pipe even if were returned to its original position.
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