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Re: Recent derailments - Metro North
Author: Dr Zarkoff
Date: 12-03-2013 - 21:42
>I'm not familiar with the current hours of service for passenger. I know that after the Metrolink Chatsworth wreck Congress changed the rules for freight train crews (HOS is a law, not just a FRA regulation), but strangely passenger rules stayed the same but were eventually supposed to have changed.
The changes to the commuter and passenger HOS requirements were nowhere nearly as substantial as those for freight. At the risk of oversimplification, they're essentially the same as before except for runs which operate between 1 and 4 AM. There are also cumulative totals involved too, but not as complicated as the freight ones.
These new requirements were the result of an RSAC/SACP process after the new law was passed, so I'm not sure whether they can be changed the same way or Congress must pass a new law (I strongly suspect it's the latter).
>Blended Braking - Never ran blended braking, but I am familiar with the basic theory.
Blended works only on the locomotive (in the MN derailment, the locomotive, a P-32ACDM, was on the rear of the train).
Passenger blended braking uses electronics to sense the amount of brake cylinder application (on the engine) caused by automatic brake applications. It puts the locomotive into dynamic braking, releasing all but a nominal amount of BC pressure in the process. I never encountered a locomotive equipped with blended braking which also had extended range dynamics, probably because the interplay of air and dynamics becomes too chancy and jerky at low speeds.
If you bail the engine, blended will either not occur or it will go away, depending on whether you bailed the engine before applying the train brakes or afterward. They will not re-apply until an increase of BC press in the locomotive is caused by another automatic application.
>You will only find it in passenger service as it is unsuitable for controlling slack in a long train,
"Blended braking" refers to the combined use of air and dynamics to control train speed, regardless of how it's accomplished. You can go into blended braking manually with either passenger or freight simply by using the appropriate throttle handles on the control stand.
Many years ago I used blended braking on a 90-100 car sugar beet train. Once you get a full service set in the train, the Boss doesn't feel a thing in the office (caboose). The results were quite impressive (also used it on a few rock trains).
And yes, blended which is automated, like in passenger locomotives, is no good at all for controlling slack in a freight train. However from what I've seen and heard of management's new way of running trains, controlling slack isn't a very high on their agenda these days.
>and it is how the dynamic brakes can be controlled by a cab car.
All the cab cars I've used have throttle positions for manual dynamic braking, which have worked just fine when needed. However, this shouldn't be taken to mean that this is universal to all cab cars all over the US and Canader. Some of the GO transit engines have blended but no provision in the locomotive control stands for manual dynamic brake operation.
>Remember that a non-dynamic brake equipped engine cannot control dynamics.
It can if the throttle stand has been equipped with the necessary controlling apparatus, not that I've ever encountered or heard of such a thing.
>Dynamics are used as the primary brake,
Dynamics are NOT a "primary brake" because they don't work when the train is not moving. This is the FRA's definition of "primary brake".
>When dynamic brake is at capacity, the system allows brake cylinder pressure to build up to the appropriate level.
No, this is when it bleeds it off to the 10 psi or so which you mentioned. The idea is to have the dynamics do as much of the work as possible until they fade (at around 11 mph)
> If there is a dynamic or blended control failure, the system reverts to normal air brake control.
This is because the blended braking lockout magnet valve becomes de-energized when the DB current goes away.
The changes to the commuter and passenger HOS requirements were nowhere nearly as substantial as those for freight. At the risk of oversimplification, they're essentially the same as before except for runs which operate between 1 and 4 AM. There are also cumulative totals involved too, but not as complicated as the freight ones.
These new requirements were the result of an RSAC/SACP process after the new law was passed, so I'm not sure whether they can be changed the same way or Congress must pass a new law (I strongly suspect it's the latter).
>Blended Braking - Never ran blended braking, but I am familiar with the basic theory.
Blended works only on the locomotive (in the MN derailment, the locomotive, a P-32ACDM, was on the rear of the train).
Passenger blended braking uses electronics to sense the amount of brake cylinder application (on the engine) caused by automatic brake applications. It puts the locomotive into dynamic braking, releasing all but a nominal amount of BC pressure in the process. I never encountered a locomotive equipped with blended braking which also had extended range dynamics, probably because the interplay of air and dynamics becomes too chancy and jerky at low speeds.
If you bail the engine, blended will either not occur or it will go away, depending on whether you bailed the engine before applying the train brakes or afterward. They will not re-apply until an increase of BC press in the locomotive is caused by another automatic application.
>You will only find it in passenger service as it is unsuitable for controlling slack in a long train,
"Blended braking" refers to the combined use of air and dynamics to control train speed, regardless of how it's accomplished. You can go into blended braking manually with either passenger or freight simply by using the appropriate throttle handles on the control stand.
Many years ago I used blended braking on a 90-100 car sugar beet train. Once you get a full service set in the train, the Boss doesn't feel a thing in the office (caboose). The results were quite impressive (also used it on a few rock trains).
And yes, blended which is automated, like in passenger locomotives, is no good at all for controlling slack in a freight train. However from what I've seen and heard of management's new way of running trains, controlling slack isn't a very high on their agenda these days.
>and it is how the dynamic brakes can be controlled by a cab car.
All the cab cars I've used have throttle positions for manual dynamic braking, which have worked just fine when needed. However, this shouldn't be taken to mean that this is universal to all cab cars all over the US and Canader. Some of the GO transit engines have blended but no provision in the locomotive control stands for manual dynamic brake operation.
>Remember that a non-dynamic brake equipped engine cannot control dynamics.
It can if the throttle stand has been equipped with the necessary controlling apparatus, not that I've ever encountered or heard of such a thing.
>Dynamics are used as the primary brake,
Dynamics are NOT a "primary brake" because they don't work when the train is not moving. This is the FRA's definition of "primary brake".
>When dynamic brake is at capacity, the system allows brake cylinder pressure to build up to the appropriate level.
No, this is when it bleeds it off to the 10 psi or so which you mentioned. The idea is to have the dynamics do as much of the work as possible until they fade (at around 11 mph)
> If there is a dynamic or blended control failure, the system reverts to normal air brake control.
This is because the blended braking lockout magnet valve becomes de-energized when the DB current goes away.
