signal apparatus

[NW Mailing List]

Abram,
Большое спасибо. Вы - умный человек.
Jim

On Thu, Jan 28, 2016 at 11:15 PM, NW Mailing List <nw-mailing-list at nwhs.org>
wrote:

>
> 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
>
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