Pennsylvania Railroad class K4
class of 425 American 4-6-2 locomotives
The Pennsylvania Railroad K4s was a class of 425 4-6-2 steam locomotives built between 1914 and 1928 for the Pennsylvania Railroad (PRR), where they served as the primary mainline passenger steam locomotives on the entire PRR system until late 1957.
Attempts were made to replace the K4s, including the 4-6-2 K5 (which had more power but the same number of drivers) and the 4-4-4-4 T1 duplex locomotive (which had both more power and more drivers). However, the low factor-of-adhesion of K5 meant that they were limited in their pulling power, while the T1's suffered from greater maintenance costs, wheel slip due to poor springing, and inexperienced crews. The T1's were also introduced late into the lifetime of steam locomotives. As such, the tried and tested K4s held their role as the PRR's primary express passenger locomotives for 30–40 years. The K4s hauled the vast majority of express passenger trains until they were replaced by diesel locomotives.
The K4s were not powerful enough for the heavier trains they often pulled from the mid-1930s onward, so they were often double-headed or even triple-headed, sometimes with early Atlantics and E6s. This was effective but expensive, and several crews were needed. The PRR did have the locomotives needed for this, many having been displaced by electrification east of Harrisburg.
The two preserved K4s, Nos.
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