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The PRR Class K-4s Pacifics

Perhaps the best-known steam locomotive of all time was the PRR Class K-4s Pacifics. This steamer carried a simple beauty to it, which also lent to much of its success. Another reason the K-4s is so popular is because almost all of the locomotives were built directly by the PRR itself in its famous Juanita shops, well over 300 in total with the remaining being built by Baldwin. Perhaps what made the locomotive so successful was the perfect blend of weight, size and powerful that allowed it to haul almost anything from passenger to heavy freight trains.

Because so many Pennsylvania Railroad K-4s' were built by the PRR it’s not surprising that they became commonplace across the system from the early 20th century practically all the way through the transition to diesels, beginning in the late 1930s through the 1940s. The PRR Class K-4s Pacifics are undoubtedly the most popular of the design ever built. In all, the Pennsylvania Railroad would come to own 424 of these masterfully crafted machines (the Juniata shops built 349 of the locomotives with the Baldwin Locomotive Works chipping in another 75) and they would carry everything from freight to the railroad’s most well-known passenger trains.

What would eventually become the PRR Class K-4s Pacifics resulted from an earlier Class E-6 Atlantic design, incorporating the 4-4-2 wheel arrangement, and the American Locomotive Company’s K-29 Pacific design. Mechanically the most famous features of the K-4s' would be their Belpaire fireboxes, 80” drivers, and Walschaerts valve gear, which blended just the right amount of power and speed to haul virtually anything the PRR asked of them.

The PRR's designation for its K-4s was as follows: the "K" denoted the railroad's fleet of Pacifics while the "4" was simply the class number of the wheel arrangement (which ranged from K-2 to K-29); lastly, the "s" referred to the class being superheated.

The PRR Class K-4s Specifications

Builder – Baldwin Locomotive Works and the Pennsylvania Railroad

Fuel - 16 tons

Cylinders(2) - 27" x 28"

Water - 7,000 Gallons

Weight - 468,000 Pounds

Diameter of Drivers – 80 Inches

Steam Pressure - 205 PSI

Tractive Effort – 44,460 Pounds

The PRR Class K-4s Pacifics were first constructed between 1910 and 1911 and they proved to be so successful that while most of their sisters of the Pacific class were retired by the 1930s they would soldier on until nearly the end when diesels began to replace all steam locomotives. The locomotive would virtually become the face of the Pennsylvania, even after the entire fleet was retired.

It should be noted that at least one PRR Class K-4s Pacific is to see active service once again; K-4s #1361 is under restoration by the Horseshoe Curve Chapter of the NRHS although its restoration is now on hold due to high costs. For more information regarding the PRR Class K-4s Pacifics please click here.

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(A deep thanks to the Museum of the Rockies at Montana State University for allowing Ron Nixon's historic collection of PRR Class K-4s Pacifics to be featured here. Please note that the photos featured on this page feature their corresponding image number so that you may quickly and easily find more information about it from their website. To view Ron Nixon's entire collection please click here.)

For more reading about steam locomotives a few books to get you started on the history of the motive power include How Steam Locomotives Really Work by authors P. W. B. Semmens and A. J. Goldfinch as well as Perfecting the American Steam Locomotive by author J. Parker Lamb. As the title of the first book illustrates, it discusses the general history of the steam locomotive and describes how it functions. In the second book you will learn how the motive power was refined over the years with newer technologies that improved the efficiency of steam to haul trains such as the superheater. There are certainly many more books on the subject of steam than these two titles. However, they are excellent starter editions on the subject and provide a very nice overview of the topic. If you're interested in perhaps purchasing either (or both) of these books please visit the links below which will take you to ordering information through Amazon.com, the trusted online shopping network.

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