From: burke@doright.Tymnet.COM (John Burke)
Newsgroups: rec.railroad
Subject: More air brake questions
Date: 23 Nov 92 22:08:30 GMT
Organization: BT North America (Tymnet)

More air brake questions

I have some more questions about air brakes.

(Thanks to the folks who answered my queries on brakes a few months ago,
esp. Steve Hooper, Mike Stimac, and Andrew Waugh.  If you would like
to know what was said, just drop me e-mail)

(My LocoCab simulator is proceeding rather slowly at present due to
my employer wanting me to WORK ... just 'cause there's a crisis!  Oh,
well.  I'm hoping to have something toward the middle of next year,
but, I don't know... .  Yes, this will be a real cab-view simulator;
queries welcome.)

Anyhow I want to simulate these details, and would like to get them
right.  QUESTIONS:

 
* What happens if the engineer keeps brakes applied for a long time, for
example, on long downhills?  And if he releases partially and then
re-applies, and does this several times?  Will this cause the various
cars to eventually have different pressures in their brake cylinders
because of their slight difference in reaction to several changes of
pressure?  Are there standard procedures and cautions for engineers,
to avoid problems here?

 
* Details of operating a 26L brake: it`s only on the New York subway that
I've had much opportunity to watch how one works a brake handle.  Their
most common brake nowadays (except on R44-46 cars) seems to work like
the mainline railroads' 26L brake: as I understand, you move the handle
farther right for a greater reduction of trainline pressure and thus
stronger braking, and left to raise pressure and ease off the brakes.
Now, what I've seen the NYC subway
motorman do normally is: throw the handle rather far right, then move it
back immediately some distance left; but after that, they use smaller
changes in position of the handle to re-adjust braking.  Application
appears to always involve a right-then-left motion, but for less
distance to get a lighter increase; while release appears to be done with
just small movements farther left.  Does this sound like the same
operation as on mainline locomotives with a 26L brake?

I also remember the pre-WW-II New York cars with the old Release-Lap-
Apply type of brake handle, like the mainline standard 24L brake;
watching the motorman work those, you could
see just where the positions were.  But I believe even some of the
old cars had special nonstandard stuff in their braking systems, like
electric brakes.


* Details of the old 24L brake control: this is the older type of
control formerly used on standard mainlines, with positions from
left to right:

	Release, Running, First Service, Lap, Service, Emergency

where in normal operation you use Service to release air, applying
brakes, Lap to hold at that pressure, and Running to pump air back
in up to normal pressure.

Question is: do the Running and Service positions have a range so
that, for example, if you move the handle farther right in Service
the pressure drops faster?

 
* Lag time: can anyone tell me what a typical lag time would be after
moving the handle to do an application or release, for some typical
train lengths, like 10 cars versus 100 cars?

* What would typical trainline pressure reductions be for 1) a very
minimal application, and 2) maximum in normal service?

* NYCTA experts: do the subway trains differ greatly from the mainline's
26L brake on these points?  I'll definitely be simulating the subway.
Maybe some other cities too.
I believe almost all New York trains still use an air line through the
train.  Exceptions: I read they experimented with an electric circuit
using voltage drop analogous to air-pressure drop.  And anybody know
what system is used in R44-46 cars?  I know these have a fancier
single-handle throttle/brake with a speed-control option.

* Gauges: which readings can the engineer/motorman see on air gauges
in typical control setups?


* Other related info which anybody has for me?