N&W's Use of PL-2 Position Light Signal Equipment

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There were only two major customers for Union Switch & Signal Company's Position Light Signals, the N&W and the PRR.  



There were three different generations of PL signal equipment: t he original PL-1 equipment which came out in the early 1920s, the PL-2 version dating from the 1930s, and the PL-3 equipment of the 1940s and 1950s.  The difference in the three generations of equipment was the optical systems  employed in the individual lamp housings... all the signal mounting hardware  remained the same through all three generations of equipment. 



The N&W was buying PL-1 equipment in the 1920s, by the 1940s had switched to the PL-2, and never appears to have used the PL-3.  The PRR, on the other hand, widely installed the PL-1, then switched directly to the PL-3 and never appears to have utilized the PL-2.  I always wondered why the N&W never upgraded to the latest PL-3 refinement, and why the PRR never used the PL-2. 



Recently I completed restoration of one each of the PL-1, PL-2 and PL-3 lamp housings, and mounted them vertically for display, and I think the  reason the N&W never bought PL-3 equipment has become  apparent. 



Using 9 volt 12 watt signal precision lamps in each, with all housings equipped with standard amber "NoViol" ("no violet") glass, and  all juiced at 5.6 volts, there are easily observed differences in the light-emitting properties of the threee generations of equipment. 



1.  The PL-1 lamps system  gives what was probably a respectable light in the early 1920s - it certainly was better than the light provided by a semaphore signal. 



2.  The PL-2 equipment (which was N&W's second-generation of Position Light Signal equipment,) with its revised optical system, gives a brilliant light, significantly better than the old PL-1, and the lens was engineered with  a horizontal band of ribbing across the middle portion of  the inside of the lens to provide a wide "spread" of light from side to side. 


3.  The PL-3 equipment (which appears to have been bought by only the PRR,) has an optical system which gives  an ENORMOUSLY brilliant light, a light which indeed  "burns the eyeballs," even when the lamps are burned at 40% below rated voltage.  However, the pencil-beam of light is si gnificantly concentrated and there is no attept to "spread" it from side to side. 



Now granted these are close-up observations and do not replicate the 2,500-3,000 range expected from a working signal in the field, but I think they answer the question why the N&W never bought the latest version of PL signal equipment.  The PL-2, with its "spread," was the perfect signal for a railroad with significant curvature problems, and the PL-3 equipment was the perfect signal for the PRR. 



During my restorations, I  photographed the optics and dead-on front views of each version of the PL equipment while illuminat ed during darkness , and as soon as I go through all the historical and technical material again, will assemble the data, the photographs and the conclusions into a PDF, and offer it to anyone who cares to read it. 



One final test remains.  The next time Mrs. Boss goes away for a few days, I shall rent a "fog machine," fill the basement up with fog, and observe the relative "fog penetrating" characteristics of the PL-2 vs. PL-3 equipment ! 



Do the N&WHS Archives contain any material relating to tests and/or purchases of  PL-2 signal material? 



-- abram burnett 

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