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PRR K4s: Map


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First K4s prototype #1737 in its official builder's photo.
Note the small tender set up for hand firing, the manual reverse, the piston tail-rods, and the oil lamp - all features that would soon change.
Dimensioned drawing.

The Pennsylvania Railroad's K4s 4-6-2 "Pacific" (425 built 1914–1928, PRR Altoona, Baldwinmarker) 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. 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. Since the PRR had often referred to itself as the Standard Railroad of the World, the K4 has sometimes been referred to as the Standard Passenger Locomotive of the World.


The K4s was designed under the supervision of PRR Chief of Motive Power J.T. Wallis, assisted by Chief Mechanical Engineer Alfred W. Gibbs and Mechanical Engineer 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 the American Locomotive Company. 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' . The boiler barrel was much fatter than previous classes, and the increase in heating surface and boiler size gave the class prodigious 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-70 tender holding only 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).

The K4s design was successful enough that it influenced other locomotive designs, and not only those of other PRR locomotives. London and North Eastern Railway Chief Mechanical Engineer Nigel Gresley incorporated much of the boiler design (including the tapered shape) into his famous Class A1 Pacific.


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 Shopsmarker 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.

Year Quantity Road numbers
1914 1 1737
1917 41 assorted numbers
1918 111 3667–3684, 5334–5349, plus assorted numbers
1919 15 assorted numbers for PRR Lines West
1920 50 3726–3775
1923 57 3800, 3801, 3805–3807, 3838–3889
1924 50 5350–5399
1927 92 5400–5491
1928 8 5492–5499

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


The PRR experimented extensively with its K4s fleet, trying out streamlining, poppet valves, smoke deflectors, driving wheel types and others.


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 in Raymond Loewy casing.
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

One of the four, #1120.
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.


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

Other Modifications

Many K4s had changes made to them, in an attempt to improve the design.


K4s 5484 was refitted with cross-counter balanced disc drivers.


K4s 5038 was given "elephant ear" smoke deflectors and a shroud for the smokestack.


K4s numbers 3676, 5399, and 5436 were fitted with booster engines on the trailing trucks in 1941.

Roller Bearings

K4s numbers 20 and 5371 were fitted with roller bearings.

Poppet Valves

K4s 5399 was rebuilt by Lima in 1939, with, among other improvements, poppet valves actuated by Franklin oscillating cams. K4s 5436 was fitted with stem actuated valves in 1940. They were designed by Lloyd Jones, the Engineer of tests at the Altoona Works. in 1945, K4s 3847 was given a front-end throttle and Franklin rotary-actuated poppet valves. All performed well, but were difficult to maintain.


K4s numbers 612, 1985, 5405, 5481 and 5484 were converted with 15" piston valves, higher steam domes and circulators, and front-end throttles.


are only two surviving K4s class locomotives. Number 3750 is on display at the Railroad Museum of Pennsylvaniamarker in Strasburg. Number 1361 was set to be restored to operation by the Railroaders Memorial Museummarker in Altoona through the restoration shop at Steamtown National Historic Sitemarker. However, due to the difficulty of overseeing the work, Altoona has halted the restoration until their restoration shop is completed. As of 2008, 1361 is sitting in pieces in a corner of Steamtown's roundhouse.


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