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Re: Pressure maintaining must work, if equipped, gooes way back.....
Author: B
Date: 04-30-2016 - 17:22
Dr Zarkoff Wrote:
-------------------------------------------------------
> >If you didn't have properly operating pressure
> maintaining operative on a 26L, you couldn't
> legitimately pass an initial terminal air test,
> cause when you made a set, and allowed it to
> equalize, before cutting out the valve to test
> train leakage, it would just continue to leak
> (bleed) down (bad gasket/baffle, if I recall
> correctly?).
>
> Yes, as explained to me by a WABCo repairman,
> early production units of the 26-L brake valve
> were prone to this, and it had to do with one of
> the materials used somewhere in the high capacity
> relay valve apparatus wearing out or hardening
> (some sort of bushing material, but it's been a
> while . . . ). The fix was to use an improved
> material. I had this happen once too and had a
> divil of a time convincing the roundhouse forces
> the brake valve was defective because it would do
> it when the train was attached and the angle cock
> open, but if you closed the angle cock behind the
> engines, it wouldn't. Being roundhouse types, they
> thought in terms of "locomotive air brake test"
> instead of "train air brake test", and it was the
> latter which mattered (not to mention specified by
> the Power Brake Law).
>
> Another problem the 26-L valve can have is that
> the high capacity relay valve's diaphragm can
> rupture, causing complete loss of control of the
> automatic air brakes, although this isn't a very
> common occurrence. It can also happen to the high
> capacity relay valve in a 30-CW module, which is
> the same apparatus, detached from the brake valve
> and placed in a different location on the
> locomotive.
>
> The most famous and humorous incident of this type
> of failure in my area involved an Amtrak train
> with and F-40. The engineer was stopping for a red
> block signal (number plate) and the diaphragm gave
> way, sending him by the signal -- this was in the
> days when you had to stop for red block signals.
> Being the rather excitable type, he got on the
> radio, wildly exclaiming "I can't stop the train,
> the brakes have failed, I can't stop the train!"
> Meanwhile the conductor is back in the coaches
> frantically trying to put his hand over the
> speaker of his pack set to keep from alarming the
> passengers needlessly (the train was going all of
> about three or four MPH when this happened). The E
> finally calmed down a bit and stopped the train
> with the jeff.
>
> For our readers: cutting out pressure maintaining
> on a 26-L is accomplished by cutting out the brake
> valve. This can also be done with any other system
> which has pressure maintaining; using the lap
> position is not always an option for doing so.
Sounds like Buckethead!!!!
-------------------------------------------------------
> >If you didn't have properly operating pressure
> maintaining operative on a 26L, you couldn't
> legitimately pass an initial terminal air test,
> cause when you made a set, and allowed it to
> equalize, before cutting out the valve to test
> train leakage, it would just continue to leak
> (bleed) down (bad gasket/baffle, if I recall
> correctly?).
>
> Yes, as explained to me by a WABCo repairman,
> early production units of the 26-L brake valve
> were prone to this, and it had to do with one of
> the materials used somewhere in the high capacity
> relay valve apparatus wearing out or hardening
> (some sort of bushing material, but it's been a
> while . . . ). The fix was to use an improved
> material. I had this happen once too and had a
> divil of a time convincing the roundhouse forces
> the brake valve was defective because it would do
> it when the train was attached and the angle cock
> open, but if you closed the angle cock behind the
> engines, it wouldn't. Being roundhouse types, they
> thought in terms of "locomotive air brake test"
> instead of "train air brake test", and it was the
> latter which mattered (not to mention specified by
> the Power Brake Law).
>
> Another problem the 26-L valve can have is that
> the high capacity relay valve's diaphragm can
> rupture, causing complete loss of control of the
> automatic air brakes, although this isn't a very
> common occurrence. It can also happen to the high
> capacity relay valve in a 30-CW module, which is
> the same apparatus, detached from the brake valve
> and placed in a different location on the
> locomotive.
>
> The most famous and humorous incident of this type
> of failure in my area involved an Amtrak train
> with and F-40. The engineer was stopping for a red
> block signal (number plate) and the diaphragm gave
> way, sending him by the signal -- this was in the
> days when you had to stop for red block signals.
> Being the rather excitable type, he got on the
> radio, wildly exclaiming "I can't stop the train,
> the brakes have failed, I can't stop the train!"
> Meanwhile the conductor is back in the coaches
> frantically trying to put his hand over the
> speaker of his pack set to keep from alarming the
> passengers needlessly (the train was going all of
> about three or four MPH when this happened). The E
> finally calmed down a bit and stopped the train
> with the jeff.
>
> For our readers: cutting out pressure maintaining
> on a 26-L is accomplished by cutting out the brake
> valve. This can also be done with any other system
> which has pressure maintaining; using the lap
> position is not always an option for doing so.
Sounds like Buckethead!!!!
