Home Open Account Help 258 users online

Steam & Excursion > “Air signal systems”, old style passenger cars & locos

Date: 01/16/22 13:29
“Air signal systems”, old style passenger cars & locos
Author: wcamp1472

Back in the day....

Passenger cars were equipped with a crude signaling system and dedicated air line
that operated a crude, shrill whistle in the loco cab.

The signal whistle system used a dedicated, smaller diameter, pipe and hoses, 
from each passenger car, or other car in a passenger train, (baggage, head-end 'freight'), etc.
The signal pipe was charged continually, when in use. All the signal valves'  car-end piping
was equipped with cut-out valves.  When the train was complete, only the signal line valve
at the rear of the train is closed ( for clarity, both the air brakes' trainline and the signal air
line valve are closed at rear of the last car).

The signal pipe. is continually pressurized from the locomotive's air-line signal system.

However, the system operates in an 'indirect' manner.  The conductor pulls and holds
the signal rope at the vestibule.   The whistle in the cab is operated by a distinct decrease
in pressure of the signal pipe.

The signal pipe is essentially a long 'air tank'.....it does not readily respond to a puff of air being
released.  So, experienced conductors pull the rope and hold it long enough to drop the
pressure in the entire air line...whether from the first car or the last car in the train.

The signal-whistle in the loco cab is sounded by a relay valve opened by the pressure drop caused
by the conductor's actions.  The signal whistle in the cab is sounded by its own (regulated) supply from
the engine's Main Reservoir.

So, the conductor must hold the valve open long enough to reduce the signal pipe's pressure,
release the rope and then allow the signal line to recharge back to full pressure, before pulling
the rope again.  

( Remember, the signal air line is constantly bring charged by a small regulator
   valve at the engine, even when the conductor pulls the rope, the regulator is sending air --
   --- thru a small hole---into the  train line signal pipe)

Soooo.  the signal to stop from the conductor is a single, long pull on the signal rope.
The Signal to ''go' is two blasts, sufficiently spaced to be distinct.

The system being indirectly operated and the volume of long signal pipes' effect on gradual
pressure changes makes the system tricky to master.

On some of O. Winston Link's station stop recordings, you can hear the masterful manipulation
of the conductor's whistle-cord operating techniques.   There's a lot to the system, but crews
that worked the trains every day were very comfortable with it's quirks, and they tested the
system at the beginning of every days' trip....they relied on it so heavily --
-- in the days before 2-way radios....

Engineers could only 'take commands' from the system.... 
They used the engine's own steam whistle to acknowledge the 
instructions from the conductor's  air signal-whistle in the cab.

Old timetables or rule books have a section on the operation of the passenger train
air signal system and the distinct commands that can be used ....
including "increase steam heat" and "decrease steam heat"...as well as other messages.  
Engineers would often respond with two blasts from his whistle as a confirmation of
the sent message..

Now, you know what those weird instructions in the rule books refer-to.



Edited 11 time(s). Last edit at 01/17/22 13:08 by wcamp1472.

Date: 01/16/22 20:24
Re: “Air signal systems”, old style passenger cars & locos
Author: joemagruder

The Sacramento Northern interurban set at the Western Railway Museum (Rio Vista Junction) has working air signals. That was part of the process of restoring SN 1005 and the other car in the consist.

Date: 01/16/22 20:45
Re: “Air signal systems”, old style passenger cars & locos
Author: wcamp1472

That's interesting..
I'd expect that with two cars in the consist, that the small volume
of the signal airlines you'd get rapid response... so the 'rope pulls' 
could be shorter and the pressure drops more distinct --- thus making
for more crisp screeches in the cab ....


Date: 01/16/22 21:57
Re: “Air signal systems”, old style passenger cars & locos
Author: krm152

Thanks very much for the comprehensive explanation.
I understood the basics but not the inner workings.
Also good to learn something new.  Thanks again.

Date: 01/16/22 22:06
Re: “Air signal systems”, old style passenger cars & locos
Author: ln844south

Had three different sizes of those "peanut" whistles. One for the communication line, one overspeed and one on the deadman's pedal. This was way  back in the day on the L&N.


Date: 01/17/22 08:21
Re: “Air signal systems”, old style passenger cars & locos
Author: engineerinvirginia

One of the early electronic alerter boxes from Quantum IIRC....had a buzzer that sounded a bit like an old peanut whistle.....done purposely I suppose. 

Date: 01/17/22 09:34
Re: “Air signal systems”, old style passenger cars & locos
Author: rrcaboose

Possibly because of numerous 'uses' during a commuter train with station stops, on EL this was a small diameter metal cable for strength and durability.
Coming into Hoboken the flagman/rear collector would signal to fireman that he was opening the steam line on rear car and to reduce steam pressure to train.

This was on diesel hauled E-L/ERIE trains and E-L/DL&W Boonton Line trains.


Date: 01/17/22 11:17
Re: “Air signal systems”, old style passenger cars & locos
Author: wcamp1472

Yes! A sensible use of the “comm-whistle”….It was a common practice to allow the
steam lines to ‘cool-down’  and also release all pressure.... for the safety of the car
department inspectors and  mechanics, as trains sometimes were uncoupled and
switched around.. 

The key component, because there were so many of them, sprinkled under the cars, was the
steam traps at all the low points…. Steam traps contained compact, sealed brass, disc diaphragms
containing alcohol.  When steam hit the traps, the diaphragms expand closing off the drain line
(leading to the ground). As the steam in the individual radiators cooled, the condensate collecteed in
the steam traps….

That condensed water soon turned cold, cooling & condensing the trapped alcohol;
thus, opening the trap ….draining the accumulated water. So, when the steam-flow
from the locomotives was stopped, it allowed the traps to open, and drain the collecting

 Often, over time the traps lost alcohol. ( meaning they were open all the time), or became
jammed-open with rust-bits, etc.  and when stuck open they blew steam.  
But, a ‘tight’ train simply dribbled condensate from all the automatic drains and had
the rear car’s end-valve cracked open, and gently blowing… thus, actually using only
a small amount of boiler steam.. 

Leaks were tremendously costly, but few wanted to spend the time to keep things tight….and
access to the faulty traps was often hard to find and a pain to repair.   Easy to do once you got under
there, but what a PITA in cold, blowy weather and you gotta spend time, stop the steam flow and
allow time to let the hot parts to cool down.  Often, the caps and covers were badly rusted abd 
difficult to get open...and a pain to try to reassemble..

Managements soon decided that keeping up with leaky traps was a fool’s errand —— especially if leaky
cars were owned by a ‘foreign’ railroad. 

 So, there’s stories about ‘P’ rr and ‘B’ rr:
"B rr heats their train by running steam through the cars:  
P rr, runs their cars through the steam!”


Sent from my iPad

Edited 2 time(s). Last edit at 01/17/22 12:36 by wcamp1472.

Date: 01/17/22 17:18
Re: “Air signal systems”, old style passenger cars & locos
Author: llafro

Many older cars (especially PVs) had the signal line converted into Amtrak's main reservoir line. We did that with our car, Tioga Pass. We removed the valves and branch pipes, but left the main part of the piping in place. Venting angle cocks and different hoses complete the changeover. So, you can say that signal lines live on.

The conductor's signal valve was still in place on the platform end until 2013, when we redid all of the platform railings. It was really tucked up inside the ralings and we couldn't get to it to remove it. I remember torch cutting the pipe and droping a bit of slag into my shoe. Hot foot!

Date: 01/18/22 07:34
Re: “Air signal systems”, old style passenger cars & locos
Author: NKP779

When NKP 765 came back to life in Dec. 1979,
it still had the steam heat and air signal lines in place.

We used the steam heat lines a lot, especially on the New River Train and even the tool car on deadhead moves. Gradually on- board generators started showing up and the car owners switched to electric. By the late 1980's there was no more call for steam heat.

There was NEVER any request to use the air signal system, not even on the New River.

During the big overhaul around 2005, the last of the steam heat and air signal lines were removed just to get rid of the unused clutter.

Posted from Android

Date: 01/18/22 08:01
Re: “Air signal systems”, old style passenger cars & locos
Author: wcamp1472

Removal, in this day and age, makes sense.
FRA rule: If equipment is 'on' the loco, it must be functional....
therefore, if not needed & not used -- remove it!



Date: 01/18/22 17:11
Re: “Air signal systems”, old style passenger cars & locos
Author: Steinzeit2

Pressure in the signal line also told the AB-1B it was entrained in a passenger or express freight consist.  Were there other non-communication uses for the signal line like that ?


Date: 01/18/22 19:08
Re: “Air signal systems”, old style passenger cars & locos
Author: agentatascadero

I can remember when this device was utilized in everyday operations.  Even as a small kid, I liked to hang out in the vestibules with the crew, and they always were accomodating...even letting me stand on the stepstool so I could see out the vestibule, and would see the pulls on the chord.


Stanford White
Carmel Valley, CA

[ Share Thread on Facebook ] [ Search ] [ Start a New Thread ] [ Back to Thread List ] [ <Newer ] [ Older> ] 
Page created in 0.0884 seconds