Jon, this assumes a big percentage of over 70 cars had pretty serious leakage.
I would really like to see what the TSB report will say on that. They would
have access to maintenance records for the cars and locomotives, and could
inspect all the equipment that was not directly involved in the fire.
Remember Joe's lifetime of experience with railroad air brakes. Sure,
technology has advanced a bit, affecting minor details, but the fundamentals
are unchanged from well before the time he started his railway career.
As Joe indicated, it is normal for cars to hold air for many hours, even many
days. I have found pressure remaining on cars weeks after they were last moved,
and these were in a museum environment where not every piece requires constant
attention to its air brakes. While individual cars in a train can certainly
leak off, there "should" be a very low percentage in such poor condition.
A couple of very important questions are raised, which I'm sure the TSB has
covered very thoroughly in their investigation:
- Were the train brakes left with a partial reduction, or fully applied when
the train was parked? In the former, pressure maintaining might maintain the
application, but certainly won't give as strong braking force as a full
reduction. Of course with full application, the trainline pressure is 0, so
pressure maintaining is not an issue.
- Were the train brakes bailed off, but the locomotive independent brakes
applied and (reportedly 11) hand brakes applied? In this case, shutting down
the units could indeed result in the independent brakes bleeding off if MM&A's
maintenance was as haphazard as many like to say.
- Were the handbrakes fully applied, or just "snug"? Were they applied while
the air brakes were engaged (making it easier to fully apply them)? The TSB was
reportedly measuring the chain still in the brake gearboxes of the destroyed
cars to gauge the number ofapplied brakes, and effectiveness of the handbrake
application.
- When the fire department was there, were there a bunch of guys wearing their
turnouts, milling around in the unlocked cab, and the train brakes were
accidentally, even partially, bailed off without being noticed? Who knows- if
the brake handle was still in application when the units coasted to a stop, we
know it didn't, but if it was in release, who did it- the engineer or somebody
else who was in the cab after he left?
-Not having any experience or training with Beltpack controls, I won't
speculate, but could the receiver have been affected by heat from the
locomotive fire, causing an unintended release? I read that the receiver on
this train was in a converted caboose coupled into the locomotive consist, so I
would think this is unlikely.
- Was the brake equipment on the affected unit in a location where the heat
could melt a seal or otherwise create a situation where a release or partial
release could occur? Not being familiar enough with the unit in question, I
won't speculate.
The comment about the EOT robbing air from the trainline should be considered a
red herring- it would only result in the air brakes reacting to lower trainline
pressure by clamping even tighter- remember, the car reservoirs do not feed air
back into the trainline. The brakes will not release unless the train line
pressure increases or the air bleeds from the reservoir, control valve, and
brake cylinder on a sufficient number of cars- a process which by rights, even
considering the grade, should take many hours- at least.
There are many issues at play here. It is my belief that no arrests should have
been made until the TSB report was released. Even then, unless the report
placed the blame directly on these men, how could they be arrested? The whole
thing reeks of third world countries, where train crews are often arrested for
accidents that were not of their making. Might the QPP have been frantically
reacting to public pressure when they should have exercised a bit more
restraint?
At any rate, this entire event, the eventual TSB report, the court cases, any
action or lack of action against the road's owners, the way Transport Canada
handles requests for regulation changes, and how the new owners of the railway
make out, and how well Lac Megantic's residents recover from this nightmarish
incident, will be of great interest for a long time.
Let's wait for the report.
Steve Hunter
From: cpsig@xxxxxxxxxxxxxxx
To: cpsig@xxxxxxxxxxxxxxx
Date: Thu, 22 May 2014 21:43:05 -0600
Subject: Re: [cpsig] Re: Fw: Central Maine & Quebec CEO: 'We'll have to prove
ourselves'
If you're dealing with road air brakes, then yes, you can be forgiven for
thinking that way. On those air brakes, air pressure keeps the brake pads away
from the disc/drum, fighting against a spring wanting to apply the brakes.
However on railway air brakes, you have a reservoir of air pressure that
applies brake shoes to the wheels. The flow of that air pressure is controlled
by the triple valve, and yes, the drop in air pressure allows the triple valve
to send air pressure from the reservoir to the cylinder applying the brakes.
With that in mind, without an air compressor feeding air into the reservoir,
leakage throughout the system (and this would very likely come from a few
places, like the EOT (these generate their power from a small nozzle stealing
some air from the train line to spin a turbine wheel and generate electricity
to charge the battery and run the electronics), imperfect couplings along the
hundred plus joints in a typical oil train of today, and all those other small
bits which allow air to escape, and soon enough, there is not enough air
pressure in the reservoirs to keep the pressure on the brake shoes. That's why
you don't need to have air hooked up to free-rolling cars going over a hump,
and why the train would have rolled away if am insufficient number of
handbrakes were set. In level trackage, 10 cars may be enough. On a grade,
with loaded cars, obviously not enough.
Jon
