PRR K4s

The Pennsylvania Railroad's K4s 4–6–2 "Pacific" (425 built 1914–1928, PRR Altoona, Baldwin) was their premier passenger-hauling steam locomotive from 1914 through the end of steam on the PRR in 1957.

Attempts were made to replace the K4s, including the K5 and the T1 duplex locomotive, but none were really successful, and the K4s hauled the vast majority of express passenger trains until replaced by diesel locomotives. Unfortunately, the K4s was not powerful enough for the weight of trains it was often called upon to haul from the mid 1930s onward, and so they were often double or even triple headed. This was effective, but wasteful in that several crews were needed. The PRR did have the extra locomotives, because many had been displaced by electrification.

Development

The K4s was designed under the supervision of PRR motive power chief J.T. Wallis and assistants Alfred Gibbs and Axel Vogt, as one of a pair of classes with the L1s 2–8–2 "Mikado", sharing a boiler and other features. A fair amount of inspiration came from the large experimental K29s Pacific built in 1911 by ALCo. Also influential was Gibbs' design for the successful E6 4–4–2 "Atlantics", from which the K4s inherited its heat-treated, lightweight machinery, its cast-steel KW trailing truck, and much in the way of general appearance.

The K4s design increased grate area from previous classes' 55 ft² to 70 ft². The boiler barrel was much fatter than previous classes, and the increase in heating surface and boiler size gave the class prodigous steam-generating capability. Equipment on the first prototype, built in 1914, was conservative and included a screw reverse (power reverse would soon be added), a small 70-P-75 tender holding only 7,000 US gallons of water and 12½ tons of coal set up for hand firing, a wooden cowcatcher pilot, a square-cased, old-fashioned headlight and piston tailrods (soon to go).

Production

Three years elapsed until production examples were constructed. Partly, this was due to extensive, exhaustive testing, but wartime necessitated priority in construction to the L1s Mikado type for freight. In 1917, Altoona's Juniata Shops started producing K4s in numbers. The first 168 carried widely scattered road numbers as traditional for the PRR, but subsequent locomotives produced after 1920 were assigned numbers in consecutive blocks.

Numbers 5400–5474 were built by Baldwin, while all others were constructed at the PRR's Juniata Shops.

Modifications

The PRR experimented extensively with its K4s fleet, trying out streamlining, different valve gear, smoke deflectors, driving wheel patterns and others.

Streamlining

A number of K4s locomotives had streamlining applied over the years, to varying degrees. All were later removed, restoring the locomotives to their original appearance.

3768

Locomotive #3768 was clad in a shroud designed by famed industrial designer Raymond Loewy in February 1936 This was a very concealing, enveloping streamlined casing which hid most of the functionality of the steam locomotive, leading to its nickname of "The Torpedo" by train crews. At first, the locomotive was not painted in standard PRR green (DGLE) but instead in a bronze color. It was later refinished in DGLE. A matching tender was also produced, running on unusual six-wheel trucks. Like most streamlined steam locomotives, the shrouds impeded maintenance and the covers over the wheels were later removed. For a time, the locomotive was the preferred motive power for the Broadway Limited.

1120, 2665, 3678, and 5338

These four locomotives were streamlined in 1940 and 1941 with simpler, closer-fitting casings that hid less of the steam locomotives' workings; in that sense, they were similar to Henry Dreyfuss's casings for NYC Hudsons.

1188

K4s #1188 was given a boiler-top streamlined "skyline" casing, but no other streamlining, and was nicknamed "The Skyline".

External links

• The Pennsylvania Railroad Pacifics at SteamLocomotive.com.
• PRR Steam Roster Pt6 – Class K.
• K4s – All of them! by Gary Mittner.