Perhaps the best-known individual steam locomotive design 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. However, beneath its good looks these 4-6-2s could also perform quite exceptionally, in both freight and passenger services. Another reason for the K-4s' popularity, at least amongst railfans and historians, was that fact that most were built the Pennsylvania's own Juanita shops, which built well over 300 in total with the remaining manufactured by Baldwin. It is important to point out, however, that the K-4s was not the only Pacific class the Pennsy owned; the railroad actually rostered over a half-dozen different types built over a 20-year span and virtually all (save for one) were listed as Class K. Today, just one of the PRR's legendary 4-6-2s is preserved and has been under a lengthy restoration process.
By the turn of the 20th century many of the larger railroads realized
that they were running into a problem; passenger trains were becoming
larger and heavier as demand steadily increased which was resulting in
multiple units needed to keep these expedited consists on a strict schedule.
In 1902 the Chesapeake & Ohio was the first to put the 4-6-2
design into regular service for the very reasons mentioned above.
Somewhat surprisingly, it was not until 1906 that the Pennsylvania
Railroad began looking at the possibility of utilizing such a locomotive
for passenger operations. In 1907 the PRR collaborated with the
American Locomotive Company's (Alco) Pittsburgh Works to build an
Interestingly, even here the railroad was still quite slow, deliberate, and calculated in its approach with the new locomotive. This first 4-6-2 was given road number 7067 and listed as Class K-28; it featured 80-inch drivers, a tractive effort of nearly 33,000 pounds, and weighed more than 208 tons (including tender). For an early Pacific design it was quite heavy in comparison to the C&O's examples (by more than 53 tons) with a tractive effort slightly better. This would be the only 4-6-2 of this class and it was later superheated and designated as Class K-28s before being scrapped in 1933. In any event, the PRR was quite pleased with its trials and decided on the Pacific as its primary power for passenger service.
The PRR Class K-4s was actually the fifth of six different classes of 4-6-2s the railroad ever owned following (by date) the K-28, K-2sa, K-21s/VK-1, K-29, and K3s. 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-inch 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; lastly, the "s" referred to the class being superheated.
The PRR Class K-4s Pacifics were first constructed between 1910 and 1911 and they proved to be so successful that while most of the railroad's 4-6-2s were retired by the 1930s they would soldier on until all steam was retired from the property in the late 1950s. Most of the 450 K-4s units were built directly by the railroad's own Juniata, Pennsylvania shop forces (375) while Baldwin also chipped in with 75 examples. Interestingly, while versatile and able to pull serious tonnage the K-4s was not Pennsy's most powerful Pacific, which was the K-5 built in 1929 that by far had the highest tractive effort, boiler pressure, and overall weight of any 4-6-2 the railroad operated. Despite their power, however, the K-5 was not considered successful on the PRR. Below is a quick snapshot of the K-4s.PRR Class K-4s Specifications
Builder – Baldwin Locomotive Works, Alco, and the Juanita Shops
Fuel - 16 tons
Cylinders(2) - 27" x 28"
Water - 7,000 Gallons
Weight - 517,225 Pounds (Including Tender)
Diameter of Drivers – 80 Inches
Steam Pressure - 205 PSI
Tractive Effort – 44,460 Pounds
Incredibly, despite the fact that hundreds of 4-6-2s were put into service on the Pennsylvania sadly only one survived the scrappers torch, Class K-4s #1361. For years this locomotive sat as a moment at the railroad's fabled Horseshoe Curve in Pennsylvania after being retired by the railroad in 1957. In 1986 the locomotive was removed from its static display and restored to operational status to pull excursions. After a lengthy rebuild beginning in the late 1990s by the Horseshoe Curve Chapter of the NRHS where millions of dollars had been spent without an operable locomotive it was decided to put the restoration on hold due to rising costs and put the Pacific on display for now.
For much more information regarding the PRR Class K-4s Pacifics 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.