Pennsylvania Railroad K4s
A K4s-hauled train pauses at Aberdeen, Maryland on 1944-04-26. This is the classic prewar K4s configuration.
Power type	Steam
Builder	PRR Juniata Shops (350), Baldwin Locomotive Works (75)
Total produced	425
Configuration	4-6-2
Gauge	4 ft 8 1⁄2 in (1,435 mm)
Driver diameter	80 in (2,000 mm)
Length	83 ft 6 in (25.45 m)
Weight on drivers	201,830 lb (91.5 t)
Locomotive weight	308,890 lb (140.1 t)
Locomotive & tender combined weight	468,000 lb (212.3 t)
Fuel type	Coal
Fuel capacity	32,000 lb (14.5 t)
Water capacity	7,000 US gal (26,000 l; 5,800 imp gal)
Boiler pressure	205 psi (1.41 MPa)
Firegrate area	69.89 sq ft (6.493 m2)
Cylinders	Two
Cylinder size	27 × 28 in (690 × 710 mm)
Tractive effort	44,460 lbf (197.8 kN)
Preserved	1361 and 3750

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, 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 was 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.^{[citation needed]}. The K4s is widely considered to be one of the greatest steam locomotives of all time.

It is recognized as the State Steam Locomotive of Pennsylvania. On December 18, 1987, Pennsylvania Governor Robert P. Casey signed into law House Bill No. 1211 naming the PRR K4 as the “official” state locomotive, according that august title to both K4 survivors, 1361 and 3750.

Development [link]

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' 55 to 70 sq ft (5.1 to 6.5 m²). 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 7,000 US gallons (26,000 l) 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.^[1]

A World War 1 era prototype, featured distinctive "chicken coop" slat pilots, while the Post-War versions were equipped with modern pilots.

Production [link]

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 [link]

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

Streamlining [link]

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 [link]

#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 [link]

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.

A streamlined K4s at the 1939 New York World's Fair.

1188 [link]

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

Other Modifications [link]

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

5484 [link]

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

5038 [link]

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

Boosters [link]

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

Roller Bearings [link]

K4s numbers 20 and 5371 were fitted with roller bearings.

Poppet Valves [link]

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.

K4sa [link]

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

Preservation [link]

3750 at the Railroad Museum of Pennsylvania

There are only two surviving K4s class locomotives. Number 3750 is on display at the Railroad Museum of Pennsylvania in Strasburg. Number 1361 was set to be restored to operation by the Railroaders Memorial Museum in Altoona through the restoration shop at Steamtown National Historic Site. 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. In 2010, the Railroaders Memorial Museum announced that the restoration was to be canceled, and the engine, when it arrives at the museum, would be reassembled and receive only a cosmetic restoration.^[2] At that time, most of the restoration was completed save for that of the boiler and other components, so it is possible that the museum may resume the restoration to operating condition in the future.

Despite the publication in the paper, museum personnel have stated though the cosmetic restoration idea was discussed, it is still museum intention to restore the engine to operating status. With the announcement of NS restarting its own steam program, there also exists, at least a little hope, of a future with a K4 under steam on the high iron.

In fiction [link]

• The Thomas and Friends character Hank is based on the K4.

References [link]

External links [link]

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