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Re: Auxiliary Braking, DPU is better
Author: ex-BN
Date: 02-10-2019 - 16:35
SP5103 Wrote:
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> >When stopped on a grade the locomotive
> independent brakes would be fully applied which
> cuts out the dynamic brake. This is why you "bail
> off" or actuate the locomotive brakes when setting
> train brakes (automatic brake) and you want to
> retain dynamic braking.
>
> Not exactly.
>
> When you apply the dynamic brakes, the Dynamic
> Brake Interlock will bail off the engine brakes.
> There are actually two standards, in one they
> truly do bail off the engine and the engine brakes
> will not apply, the other standard is if you get
> out of dynamics any automatic brake application
> will reapply on the engine unless you have
> manually bailed it off. BN may have had a third
> standard, limiting the dynamic braking effort to a
> minimum once brake cylinder pressure reached a
> certain pressure.
On older BN power (SD40-2) you did indeed lose all dynamic after the independent pressure reached a certain point--a bit above 10 pounds as I recall. There was no automatic bailing of the independent brake in dynamic on BN engines then. I have handled non-BN power that had that feature and perhaps the newer power on BNSF does. Also BN was very late to the extended range and high capacity dynamic brake game. (Perhaps starting with the GP50s of the mid '80's.) So we had plenty of practice using air on mountain grades.
-------------------------------------------------------
> >When stopped on a grade the locomotive
> independent brakes would be fully applied which
> cuts out the dynamic brake. This is why you "bail
> off" or actuate the locomotive brakes when setting
> train brakes (automatic brake) and you want to
> retain dynamic braking.
>
> Not exactly.
>
> When you apply the dynamic brakes, the Dynamic
> Brake Interlock will bail off the engine brakes.
> There are actually two standards, in one they
> truly do bail off the engine and the engine brakes
> will not apply, the other standard is if you get
> out of dynamics any automatic brake application
> will reapply on the engine unless you have
> manually bailed it off. BN may have had a third
> standard, limiting the dynamic braking effort to a
> minimum once brake cylinder pressure reached a
> certain pressure.
On older BN power (SD40-2) you did indeed lose all dynamic after the independent pressure reached a certain point--a bit above 10 pounds as I recall. There was no automatic bailing of the independent brake in dynamic on BN engines then. I have handled non-BN power that had that feature and perhaps the newer power on BNSF does. Also BN was very late to the extended range and high capacity dynamic brake game. (Perhaps starting with the GP50s of the mid '80's.) So we had plenty of practice using air on mountain grades.
