N&W CPL signals

nw-mailing-list at nwhs.org nw-mailing-list at nwhs.org
Sat Aug 12 21:58:24 EDT 2006


What you are looking for is a Position Light "dwarf signal."

They were used at interlockings on tracks where trains would be approaching at what was originally called "Low Restricted Speed" (i.e. 15 MPH or less) and therefore where a long "preview" (range) would not be required. Because range of required "readability" of the signal was short, there was no focusing mechanism afforded for the optics (no parabolic focusing mirrors; no compound lenses; no "signal precision" lamp having its filament within 1/64th inch of the optically precise focal point behind the lens, etc.)

Specifically, these were Union Switch & Signal styles PL-2 (old) and PL-4 (modern.) The PL-2 had the arc in the 12 o'clock to 3 o'clock quadrant. The PL-4 had the arc in the 9 o'clock-to-12 o'clock quadrant. The change in the location of the arc from one side of the signal to the other was made for clearance reasons, as engines and their cylinders grew bigger.

Also, access to the lamp sockets was greatly improved when US&S came out with the PL-4. On the old PL-2s, there are two side plates which are removed to gain access to the lamps. Even a signalman with tiny hands gets skinned knuckles when re-lamping one of the old PL-2 signals. However, on the PL-4s, the entire back of the signal case is removable, affording easy access to everything.

On the N&W, there were no colored lenses in these signals until around 1960. Between the lamp and the outer lens (a.k.a. roundel,) there was only a disc of frosted glass called a "diffuser." For this reason, the individual illuminated roundels appeared to have a color ranging from white to ivory, depending largely on how much below rated voltage the lamps were being burned. Beginning around 1960, when the N&W added color to its Position Light signals, the clear frosted glass diffusers were replaced with amber, red, or whatever color diffusers. Personally, I liked the old non-colored version better, but your mileage may vary...

-- abram burnett
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