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Re: I think the engineer was trying to make up time
Author: Dr Zarkoff
Date: 10-15-2020 - 12:48
> It seems there would have to be provision to make a corresponding brake pipe reduction (to equalize with the reduced aux reservoir pressure) after an E-application, or the automatic brake valve on the engine left in "running" position would result in continued recharging of the aux reservoirs.
Finally found something buried near the end of a paragraph: the BP was maintained at full pressure in order to keep the service and release pistons in the D-22 control valve(s) in their release positions during E-brake applications.
> Perhaps it was necessary to put the automatic in "lap" when using the E-brake (?),
Apparently not, see above.
> or perhaps the control valves on the cars had provision to prevent recharging when an E-application was made.
Not specifically mentioned, but continuously recharging the auxiliary reservoirs (on the cars) keeps the car magnet valve air supplies topped off, which would enable a series of applications (pressurizations of the straight-air pipe) and releases to be made in a short period of time without the loss of brake performance experienced with all-pneumatic train brake systems.
>In that case, it seems that a quick switch from E-brake to automatic (such as in the event of E-brake failure of some sort) would require going extra deep with the automatic to "catch up" with the existing reduction in the aux reservoirs.
Not so much "extra deep" as "equaling the balance point between the auxiliaries and the brake cylinders". Emergency applications were covered by a the A-1 brake application valve on the engine, and on the cars by the quick action features of the D-22 control valves.
> Essentially like working with a "soft" brake pipe.
"Soft brake pipe"? Do you mean "undercharged auxiliaries"? I once heard an "old head" use the term "soft-piping it", so I asked him about it. He described a process which essentially amounted to trying to make graduated releases with freight control valves. This is simply not possible because there is no way to raise auxiliary reservoir pressure unless the control valve's operating piston is in the release position. Passenger control valves have a special port which does this, using a separate air supply on the car. This continues to raise auxiliary reservoir pressure once brake pipe pressure stops rising, and when aux pressure slightly exceeds brake pipe pressure, it then forces the operating piston to lap.
What that old head was doing was using the flaky operation of the control valves on an unknown number of the cars in the train to produce a reduced retarding effect.
The problem with all these cute terms the old heads used, is that very few, if any, actually understood how the systems worked, and they were just repeating gossip they heard from others in order to be "one of the cool guys". In order to grandstand with a brake system, it's necessary to understand how it works with a fair degree of accuracy because over the years, WABCo built in a lot of measures designed to prevent just such grandstanding.
Finally found something buried near the end of a paragraph: the BP was maintained at full pressure in order to keep the service and release pistons in the D-22 control valve(s) in their release positions during E-brake applications.
> Perhaps it was necessary to put the automatic in "lap" when using the E-brake (?),
Apparently not, see above.
> or perhaps the control valves on the cars had provision to prevent recharging when an E-application was made.
Not specifically mentioned, but continuously recharging the auxiliary reservoirs (on the cars) keeps the car magnet valve air supplies topped off, which would enable a series of applications (pressurizations of the straight-air pipe) and releases to be made in a short period of time without the loss of brake performance experienced with all-pneumatic train brake systems.
>In that case, it seems that a quick switch from E-brake to automatic (such as in the event of E-brake failure of some sort) would require going extra deep with the automatic to "catch up" with the existing reduction in the aux reservoirs.
Not so much "extra deep" as "equaling the balance point between the auxiliaries and the brake cylinders". Emergency applications were covered by a the A-1 brake application valve on the engine, and on the cars by the quick action features of the D-22 control valves.
> Essentially like working with a "soft" brake pipe.
"Soft brake pipe"? Do you mean "undercharged auxiliaries"? I once heard an "old head" use the term "soft-piping it", so I asked him about it. He described a process which essentially amounted to trying to make graduated releases with freight control valves. This is simply not possible because there is no way to raise auxiliary reservoir pressure unless the control valve's operating piston is in the release position. Passenger control valves have a special port which does this, using a separate air supply on the car. This continues to raise auxiliary reservoir pressure once brake pipe pressure stops rising, and when aux pressure slightly exceeds brake pipe pressure, it then forces the operating piston to lap.
What that old head was doing was using the flaky operation of the control valves on an unknown number of the cars in the train to produce a reduced retarding effect.
The problem with all these cute terms the old heads used, is that very few, if any, actually understood how the systems worked, and they were just repeating gossip they heard from others in order to be "one of the cool guys". In order to grandstand with a brake system, it's necessary to understand how it works with a fair degree of accuracy because over the years, WABCo built in a lot of measures designed to prevent just such grandstanding.
