Steam & Excursion > From the “Air signal systems” thread…

AB-1-B valve in 'freight' /express cars routinely used in passenger trains.
It was an air-brake compromise, add-on device, to allow smoother station stops,
if there were a lot of 'head-end' ( freight-brake equipped) cars in the trains.

( First, a side-discussion on distinctions between evolving 'freight' and 'passenger'
  air brake valves under railway cars:

    The primary distinction between freight brakes and passenger brakes, that's easy to
   remember, is that when brake pipe pressure is being increased/restored, following a
   'reduction',  say from 100 lbs pressure back to 110 lbs 'release'  the pressure acting
    on the brake's piston [applying the brake shoes to the wheel tread],  in the AB-types
    [freight car specific], the brake cylinder pressure is completely exhausted.  

    AB-type valves are intended for freight service, and, when releasing, all the air in the
    brake cylinders is released at once  [ there is a way to manually modify the pressure --
   ----- but, that's for a different discussion]..).



 In passenger cars, for nice, smooth station stops, the engineer can reduce the original --
 deep application---  in gradual steps.  
Like, from a twenty-pound reduction to a 10-pound reduction.  

  The amount of braking-force needed at 60MPH.... might be greater than what is needed below
   25-MPH.   So, if the 'heavier' reduction is too 'strong', as the train slows to under 20-MPH,
   it might STOP --- all at once ---- way too short of the station ahead...

  So, to allow the train to roll easier, the passenger engineer is able to release some of the air from the
  brake cylinders,  yet keep the shoes applied under less pressure.  
  He's able to make a partial release  of  cylinder pressure... and roll to a nice, smooth stop.

  On passenger car air brake control valves there is an 'option' to choose either 'direct' release,
  or 'graduated' release --- typically a bolted-on cap, with 1 of two settings, is set to the desired 
  service.  

If passenger cars are sometimes hauled in freight trains, you ALWAYS want to set the bolted-cap 
to 'Direct' release, that way the shoes always fall away from the treads as BP air is restored after
a 'service application'.    If in 'graduated' release, and back in the train many cars, the brake shoes
 too often were jammed against the wheels...and often failed to fully 'let-go'.

So, many 'head-end' baggage and express/mail cars were only fitted with freight-intended
air brakes, the AB-style, 'direct release' brake valves.... 

The AB-1-B 'module' was applied to the AB-type valves on those express/ mail cars that allowed
less-than-full brake cylinder pressures applied to the brake pistons.   An input line ---- from the
passenger air-signal line --- to the AB-1-B 'module' was used to reduce the brake shoe application
pressure,  when such, AB-type brakes,  cars were used in  a passenger train.

The reduced pressure action, in the AB-equipped, was a 'rough approximation' using a lighter
brakes application, lower cylinder pressures  ---- so that passenger cars after the head-end cars
wouldn't all jam agsinst the Mail/express cars with the 'all-or-nothing' brakes and no
'graduated release' option.

Many automobile drivers, like for red-aspect traffic-lights, will slow down with a stiffer brake pedal
pressure, and a lighter pressure as the car draws closer to the stopped cars ahead..
"Graduated Release"😃

​W.



Edited 12 time(s). Last edit at 01/19/22 19:15 by wcamp1472.

A very competent friend responded privately to the discussion.
His point was that more modern developments added axle,
individual, electrical signal generators, better brake shoes ,
and automatic "Blended"  braking systems etc.

( "Blended brakes"  --- passenger trains--- refers to locomotive
dynamic brakes slowing the higher speeds, seamlessly switiching over to
air brakes for further slowing and stopping -- all automatically, using
conventional controls.).

So, the earlier days of exclusive, air-operated brakes was necessarily
upgraded as technology advanced.  

Today's passenger trains' braking schemes are very complex, and 
require great skill to maintain.....yet, they remain easy and intuitive to 
operate, from the engineer's operating standpoint.

The various modes, speed determined, --- operate smoothly when bringing 
passenger trains to a stop.

Its way more difficult to bring 'electricallly modulated' braking systems to
freight trains ---- there's millions of freight cars that are equipped with only 
single-pipe air braking.  How do you upgrade that entire freight fleet
to "all-electrical braked",  air-operated brakes for every/all the freight cars?  
Can the 'new system' accommodate a mix of old and new technologies 
all in one train?

How do you equip every locomotive to the 'modern' state of freight train
braking controls ---- as well as controlling trains 2 to 3 miles long? 
Obviously, coded, radio signal commands will be used.
That's the primary challenge --- entire "fleet upgrading".

Eventually, those 'upgrades' will be mandatory for any operable steam locomotives,
if they're to venture out of their museums onto America's rail network.

​W.


 



Edited 1 time(s). Last edit at 01/20/22 07:48 by wcamp1472.

Southern Pacific, for many years included instructions in their book of operating rules
regarding the procedures to follow when any car in a passenger train experienced a 
broken brake pipe. The communicating signal pipe on that car was used to, in effect,
'wrap around' the defective car by coupling the brake pipe ahead of the 'broken' car to
its signal pipe and, at the rear of that 'broken' car, re-route the signal pipe back to the 
brake pipe of the following cars; making sure to drain all air reservoirs on the 'broken' car.
SP concluded the instructions by noting that the communicating signal on all cars to the
rear will be inoperative. For that reason trainmen were instructed to "...use hand signals
in lieu thereof."

The day our engineers class underwent it's 'oral' examination for promotion, the Road Foreman
of Engines holding forth at that auspicious moment spent a few minutes describing the dangers
involved with opening a discharge valve on any car beyond the broken train line: likely an
emergency B.P. application.

Charlie

Re: above 'story' about  repurposing the piping....
( not a plausible fault)

Since the 'trailing cars'  signal line would be cut off from any signal
function & connection at the Failed Car...there was NO danger of
an 'Emergency' application from a 'mistake' in the trailing cars,
behind the 'trouble' car.  

Their signal lines and operating valves would be dead.

The repurposed pipe only affects the 'problem' car.  
The trailing cars' air signal feature would be inoperative.

The only car who's signal pipe would be utilized as a 'brake pipe',
is the one which had the 'problems'.  Any other trailing cars were
simply fed train line air through to their own, unaltered, piping.

There would be NO functioning/pressurized signal air piping after
the 'problem' car, and the signal air line hose at the Front End of the
trailing cars would not be connected (at the rear of the 'problem' car). 
The trainline hoses at each end of the 'problem' car would have
been reconnected to the 'signal pipe"--- and used it as a straight-thru
brake pipe....to any trailing cars.**

I am not sure that the signal-line's smaller piping, hoses and 'glad hands'
would function with the 1 1/4" trainline hoses and fittings
( I think the signal air line is 3/4" pipe, hose & fittings).

It might take reducing pipe couplings to be functional...?
Its all moot now, anyway.

​W.

( The only way to prevent unintended brakeshoe application on the  
   'problem' car is to drain & deplete all the air reservoirs under the
   car with the by-passed airline..... which includes no air for any
    water-using plumbing appliances, on only one car).

**( It would NOT be good to have such a  crippled car [ no functioning brakes]
      as the last car of a train.  it would be BEST to have it mated [ using blocked
      uncoupling pins]  with a car behind it with operable brakes --- where the two
      could be handled as a ',matched pair' ......all the way to the repair 'track'...
      for proper repairs and restoration of all affected piping.).

 



Edited 9 time(s). Last edit at 01/21/22 10:23 by wcamp1472.

wcamp1472 Wrote:
-------------------------------------------------------
> Re: above 'story' about  repurposing the
> piping....
> ( not a plausible fault)

I'm curious, what is meant by: "(not a plausible fault)"?

Charlie
  

". ...opening a discharge valve on any car
> beyond the broken train line: likely an
> emergency B.P. application...."

What is meant by the wording: 'discharge valve', as used above?
'Discharge' from which pipe?

​W.

 

wcamp1472 Wrote:
-------------------------------------------------------
> ". ...opening a discharge valve on any car
> > beyond the broken train line: likely an
> > emergency B.P. application...."
>
> What is meant by the wording: 'discharge valve',
> as used above?
SP's term as in "When transmitting signals, the length of the train determines the discharge valve timing"

> 'Discharge' from which pipe? 
Signal pipe.

CEW​


  

Is the 'mistake' made in the car that's been 'modified'
in the "work-around",   or the from 'healthy' cars behind the 'defective' car?

W.

wcamp1472 Wrote:
-------------------------------------------------------
> Is the 'mistake' made in the car that's been
> 'modified'
> in the "work-around",   or the from 'healthy'
> cars behind the 'defective' car?

If, by 'mistake' you are referring to opening the discharge valve on the 'modified' car, yes that action could cause
an emergency brake pipe application since the signal pipe on that car is now carrying 110lbs and the sudden drop
in brake pipe pressure in either direction from the 'modified' car could possibly trigger an emergency application. 
The 'mistake' could not have originated from any car behind the 'defective' car as there is no pressure in those
signal pipes---after the wrap-around was made. Another peril that rears its ugly head, is that improper operation of a
discharge valve (in this case, any operation) brings forth the possibility of an unintentional release of a brake pipe 
application, if in effect at that time. 

CEW

"Road Foreman
> of Engines holding forth at that auspicious moment
> spent a few minutes describing the dangers
> involved with opening a discharge valve on any car
> beyond the broken train line: likely an
> emergency B.P. application...."



""opening a discharge valve on any car
> beyond the broken train line...'

I  was confused by the wording "on any car beyond the broken train line"...
I don't see how pulling the signal cord on the trailing cars could affect the train line.....
since all cars behind the "problem" car would have no pressure in their signal lines.

So, he was supposedly talking about inadvertent use of the signal line only on the
'work-around' car?

Thanks for the discourse.

​W.



Edited 2 time(s). Last edit at 01/21/22 16:26 by wcamp1472.

wcamp1472 Wrote:
-------------------------------------------------------
> "Road Foreman
> > of Engines holding forth at that auspicious
> moment
> > spent a few minutes describing the dangers
> > involved with opening a discharge valve on any
> car
> > beyond the broken train line: likely an
> > emergency B.P. application...."
>
>
>
> ""opening a discharge valve on any car
> > beyond the broken train line...'
>
> I  was confused by the wording "on any car beyond
> the broken train line"...
> I don't see how pulling the signal cord on the
> trailing cars could affect the train line.....
> since all cars behind the "problem" car would have
> no pressure in their signal lines.
>
> So, he was supposedly talking about inadvertent
> use of the signal line only on the
> 'work-around' car?

That's a possibility. Unfortunately that meeting was 52 years ago and it's not possible to ask any 
of the four Road Foremen who were present that day to elaborate further. I know I had a hard time
remembering my own name that day! Thank you.

CEW