Fwd: signal apparatus

[NW Mailing List]

Abram,

>From your message I now understand the 'odd' signals that are seen at the
21:04 - 21:24 time mark in N&W's film 'The Modern Coal Burning Steam
Locomotive' (see link below). I had always wondered why there were triple
arms on these signals. And you'll also notice the 'forth arm' that you made
reference to at the bottom of each mast. This is a beautiful signal bridge
and now it means more to me because I understand it's purpose. Does anyone
know its location? Thanks for telling us "how to build a clock"! I love it!

John Garner
Newport, VA

https://www.youtube.com/watch?v=0TDgyTOjXwE&list=PLpQhyadbJjLQIhdNMmhNIyrLN_
FbDY2m2


Message: 2
Date: Fri, 29 Jan 2016 04:15:53 +0000 (UTC)
From: NW Mailing List <nw-mailing-list at nwhs.org>
To: N&W Mailing List <nw-mailing-list at nwhs.org>
Subject: Fwd: signal apparatus
Message-ID: <mailman.2746.1454067678.1171.nw-mailing-list at nwhs.org>
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The "boxes" you inquire about on the signal cantilever are old semaphore
cases. They originally housed the motor and sprocket-and-chain drive
apparatus for operating old Style S and Style B semaphores, along with the
track relays and relays for line circuits. 

You have seen many, many of these on the old N&W, but they were on the
ground, not on a signal bridge. 

When N&W installed PL signals, they used simply removed the semaphores arms
and motors, and mounted the new PL's on the old masts and cases. 

One reason the masts for N&W PL signals were so high is that they originally
were built for the spacing of two and sometimes three semaphore arms, which
required more room than PL signals. 

Two semaphore arms (again, don't say "heads"... that's a weenie word) were
required to give the indications which could be displayed on one PL arm. And
THREE semaphore arms were required to give the indications that could be
displayed on two PL arms. So, it was necessary that semaphore masts be
higher. 

There is also another reason for the height of the old semaphore masts, and
although it goes beyond the scope of your question, I will explain it. In
semaphore days, there was a notion that the ideal way to locate a semaphore
was so that, when sighted by the Engineman, the signal arms were viewed
against the sky. It was felt that if trees, mountains and the like, formed
the background, they "competed" with the visibility of the semaphore arms.
This was the fundamental reason for the very high masts, and it was good
thinking. One additional benefit of such an arrangement was that it raised
the signals up above the pall of smoke which often hung over heavily
trafficked, double track main lines. But apparently not all railroads
subscribed to this notion. For example, the Santa Fe had remarkably low
semaphores, whether they be bridge signals or ground mast signals. 

Allow me one further ramble... If you compare the 1938 N&W Rule Book (the
rule book which first depicted PL signals) with the 1928 Rule Book (which
depicted only semaphores,) you will discover a very interesting thing. To
wit, that when the N&W first installed PL's, they used them for NOTHING MORE
than replicating, with rows of lights, the positions of the old semaphore
arms. That is to say, if the old semaphore had three arms, the N&W replaced
it with a three arm PL. Now that is truly amazing, especially since someone
had worked out, in 1922, a system of giving a full set of signal indications
with only TWO PL arms. (His name was Alexander Holley Rudd, and he was the
Chief Signal Engineer for another railroad.) 

To exacerbate this, below the three full PL signal arms, the N&W sometimes
used a "marker light" at the bottom. Technically, that constitutes a "four
arm" signal. It's function was to show that the signal was not an automatic,
and that its most restrictive indication was Stop, not Stop and Proceed.
When these marker lights were removed from the masts, the hubs were left on
the masts and a blanking plate was placed over the opening in the hub. Those
old hubs, which formerly held the marker lamps, can still be seen on many
N&W PL signals. 

If you look at the 1945 N&W Rule Book, you will see the same three arm PL's
shown that were shown in the 1938 Rule Book. 

If you check the 1951 N&W Rule Book, however, the old three PL arm signals
are gone. Someone in the N&W Signal Department had learned about the PL
signal arrangements created by Alexander Holley Rudd in 1922, the old third
arms had been removed, along with the bottom marker lamps, and a full set of
indications was now being given with just two PL arms. The new, more simple
arrangement saved relays, a lot of wire, lamps and electricity. 

By the way, when referring to the arms on a signal, they may be referenced
two ways. The standard plans and engineering prints designate them as the A,
B and C arms. But in conversation, they are usually called the top, middle
and bottom arms. 

You asked me for the time, and I told you how to build a clock. But
sometimes too much information is better than too little. 

And some day, if you want to know about FIVE arm signals, we can have
another interesting discussion!  But that one will involve some very, very
deep history.

-- abram burnett,
a simple turnip farmer