Pennsylvania / Vandalia Line 4-6-2 "Pacific" Locomotives in the USA

The Early PRR "Pacifics", Classes K-28, K-2, K-2a, K-2b, & K-3s

By 1906, the weight of passenger cars had become so heavy that double-heading passenger trains was becoming a regular occurrence in order to maintain schedules. The PRR was looking for a new more powerful locomotive and bought its first "Pacific", an experimental 4-6-2 built in 1907, by the Pittsburgh Works of the American Locomotive Company. This single locomotive was designated as Class K-28 and given road number 7067. It had 80" drivers, 24 x 26 cylinders, a boiler pressure of 205 psi, exerted 32,620 lbs of tractive effort and weighed 273,600 pounds. The tender used on this locomotive carried 7,350 gallons of water and 12 tons of coal. The railroad tested number 7067 for a few years and finally determined that this was the type of locomotive it wanted for its passenger service.

The Juniata Shops in Altoona, PA began constructing 4-6-2 locomotives in 1910 and by 1911 had built 153 very similar copies of the ALCO built "Pacific" bought in 1907. These locomotives were designated as Class K-2 and were assigned road numbers scattered from 23 through 9999. They had 80" drivers, 24 x 26 cylinders, a boiler pressure of 205 psi, exerted 32,620 lbs of tractive effort, and weighed 278,800 lbs with 185,900 lbs on the drivers. The tenders carried 7,100 gallons of water and 16 tons of coal. There was a "ghost" class K-1, a design which had a smaller boiler and lower pressure than the Class K-28. The K-1 design was rejected without a single example being built.

A slight modification was made to the design of the Class K-2, in late 1911, the firing deck was raised to accommodate stokers. The Juniata Shops produced 62 of these modified locomotive which were designated as Class K-2a, between 1911 and 1913. ALCO was given an order and delivered 10 of the Class K-2a locomotives in 1912. These 72 Class K-2a 4-6-2s were numbered with scattered road numbers from 86 through 8543. Though designed to have stokers only a few were actually installed.

Another two "Pacific" were built in 1911. They were very similar to the Class K-2 locomotives except they had 72" drivers. This pair was designated as Class K-2b, with road numbers 3371 and 3375 assigned.

In 1913, the Baldwin Locomotive Works built 30 more "Pacifics" for the PRR. These were very similar to the Class K-2 locomotives except they had larger cylinders (26" dia.) were super heated and equipped with mechanical stokers. With the larger cylinders they exerted 38,280 lbs of tractive effort. This group was designated Class K-3s and given scattered road numbers from 7004 through 8663.

In all, 257 "Pacifics" were built based on the 1907 experimental Class K-28.


The "Standard Passenger Locomotive" Class K-29 & Class K-4

In 1911, the PRR had the American Locomotive Company build another 4-6-2 experimental locomotive. It had a very large boiler and a radial stay type firebox with brick arch. It incorporated outside steam delivery pipes, stoker, screw reverser, superheater and other innovations of the day. The specifications included 80" drivers, 27 x 28 cylinders, a 200 psi boiler pressure, a tractive effort of 43,375 lbs, 197,800 lbs on the drivers and a total weight of 317,000 pounds. The tender carried 8,280 gallons of water and 14 tons of coal. This single locomotive was designated as Class K-29 and had road number 3395.

Satisfied with the performance of the Class K-29 locomotive the PRR built a similar locomotive in the Juniata Shops and it was put into service in 1914. This locomotive was given road number 1737 and was designated a Class K-4s. Number 1737 was put through an extensive testing program and was found to be an excellent locomotive. The railroad had a top priority order for 2-8-2 "Mikados" going through the Juniata Shops and the Class K-4s "Pacifics" would have to wait until 1917 before the shop could begin to build them.


Starting in 1917 and continuing through 1928 the Juniata Shops built a total of 349 of the K-4s "Pacifics" and the Baldwin Locomotive Works built 75 of them. These locomotives were given the following road numbers:

K-4 Assigned Road Numbers

8, 12, 16, 20, 43, 122, 225, 227, 262, 269, 295, 299, 358, 359, 383, 389, 422, 452, 518, 526, 612, 623, 646, 669, 719, 830, 837, 850, 911, 920, 945, 949, 958, 962, 1120, 1139, 1188, 1195, 1329, 1330, 1339, 1361, 1392, 1395, 1433, 1435, 1436, 1453, 1462, 1488, 1497, 1517, 1522, 1526, 1531, 1533, 1546, 1551, 1554, 1588, 1653, 1737, 1980, 1981, 1983, 1984, 1985, 2032, 2034, 2112, 2445, 2665, 2673, 2761, 3654, 3655, 3667 through 3684, 3726 through 3775, 3800, 3801, 3805, 3806, 3807, 3838 through 3889, 5022, 5038, 5041, 5058, 5072, 5077, 5086, 5147, 5154, 5238, 5243, 5253, 5296, 5334 through 5399, 5400 through 5499, 7053, 7054, 7116, 7133, 7244, 7267, 7270, 7273, 7274, 7275, 7278, 7279, 7280, 7287, 7288, 7914, 7938, 8009, 8068, 8085, 8108, 8114, 8122, 8137, 8157, 8161, 8165, 8181, 8195, 8212, 8218, 8225, 8236, 8240, 8242, 8251, 8261, 8278, 8281, 8309, 8334, 8347, 8373, 8377, 8378

The Class K-4 locomotive was a splendid machine and the designed incorporated many of the outstanding features of the earlier Class E-6 "Atlantic" (4-4-2) passenger locomotive plus technology developed for the earlier "Pacifics" and the the ALCO Class K-29. Also some of the design features of the Class L1 "Mikado" (2-8-2) freight were made part of the K-4s design.

The heart of the design was its long tapered boiler with its huge square shouldered "Belpaire" firebox. The six 80" drivers were moved by light weight, hollow ground piston rods, crossheaders and nickel-chrome steel main side rods, regulated by Walschaerts valve gear.

There were eight different styles of tenders used with the Class K-4s locomotives. They ranged form the original tender with a capacity of 7,000 gallons of water and 12 1/2 tons of coal to the so-called "Coast-to-Coast" tender with its capacity of 22,090 gallons of water and 31 1/2 tons of coal. And in between some of the "Mountain" tenders were used with the K-4s. In the 1930s Mechanical Engineer W. F. Kiesel, Jr designed three new tenders for use with the K-4s. They were, the Class 90-P-75 (9,700 gallons of water and 21 tons of coal), the Class 110-P-75 (11,980 gallons of water and 18 1/2 tons of coal) and the Class 130-P-75 (13,475 gallons of water and 22 tons of water).

By the late 1930s, 75% of the earlier classes of "Pacifics" had been scrapped, but only one of the K-4s locomotives had been lost. Number 8309 derailed in Pittsburgh, PA on December 27, 1937. and it fell off a cliff and was damaged beyond repair. It would be almost ten more years before another one of the K-4s would be retired. So it was the remaining 424, Class K-4s "Pacifics" (and the GG1s) that were the work horses that pull most of the passenger trains during railroads busiest decade, the 1940s,

The Pennsylvania Railroad often referred to itself as the "Standard Railroad of the World" and to millions of rail travelers, millions of servicemen during World War II, and railfans for over 80 years, the Class K-4s was, and to many still is, the "Standard Passenger Locomotive".


Class K-4s Improvements

While in service, some of the Class K-4s locomotives were fitted with all kinds of innovations for test purposes. These innovations included streamlined shrouds, roller bearings, poppet valves, disc drivers, smoke deflecters, boosters and many others.
Streamlined Shrouds
In the mid 1930 streamlining steam locomotives for passenger service was tried as a way to lure the traveling public back to rail travel and away from the automobile. The PRR turned to industrial designer Raymond Loewy to design a shroud for the Class K-4s locomotive. Loewy and the PRR converted number 3768 into a very fine looking streamline locomotive in 1936.


Later, in 1940 and 1941 four more K-4s locomotives received a streamlined shroud. This shroud was of a more simple design as compared to the 1936, Loewy design. The four were road numbers: 1120, 2665, 3678, and 5338. Eventually, all five of the streamed locomotives had their shrouds removed were restored to their original appearance. Another locomotive, number 1188, did not get a full streamline shroud, but did get a boiler top cowling and was dubbed "The Skyline".

Throughout the course of normal routine maintenance, many streamliners had their streamlining removed. The Pennsylvania Railroad was particularly guilty of this. Their K-4 locomotives received a much more thorough shrouding than the J-3 in 1938, when both railroads introduced new lightweight versions of the Broadway Limited and 20th Century Limited, on the same day. Within days, the PRR removed the lower sections of their K-4's shroud, just to make access to the drivers easier. In a few weeks, the shop forces would fail to refasten other sections of the streamlining, and by 1939, when Lucius Beebe got around to photographing the Broadway Limited, he was upset at "its singularly unbuttoned appearance." The front coupler was exposed and the rest of the shroud looked ragged and torn.

Raymond Lowey not only designed the shroud of the K4, he wrote a book about it and compared it to European and American streamlining efforts. He claims his PRR commissions were the "epitomy of streamline theory". If you are talking electric locomotives, then Raymond Lowey is probably right, since he did style the carbody of the GG1, but nobody thinks his K-4 is close to the New York Central's J-3 in terms of beauty. In fact, the PRR's streamlined locomotives were downright ugly, with the possible exception of the T-1, a 4-4-4-4 which looked a lot better than it performed.

Roller Bearings
Two K-4s were fitted with roller bearings. They were road numbers 20 and 5371.
  • 20 (1932, photographer unknown, Carl Weber collection. Note roller bearings on trailing truck and tender.)
  • 5371
Poppet Valves
K-4s number 5399 was rebuilt by the Lima Locomotives Works in 1939, to include poppet valves actuated by Franklin oscillating cams along with other improvements. The drawbar HP was increased by as much as 44% at speeds between 60 and 80 mph.

Number 5436 was fitted with steam actuated valves designed by the Altoona Works Engineer of Tests, Lloyd Jones. The valves were installed in 1940. In 1945, another K-4s, number 3847 was equipped with a front end throttle and Franklin rotary-actuated poppet valves. All of the poppet valve applications did a good job especially at higher speeds. However, they were difficult to maintain.

Disc Drivers
K-4s number 5484 was refitted with cross-counter balanced disc drivers,
Smoke Deflecters
K-4s number 5038 was equipped with huge "elephant ear" smoke deflecters along with a shroud for the stack.
Numbers 3676, 5399 and 5436 were the only K-4s locomotives to befitted with boosters. The boosters were on the trailing trucks and were installed in 1941.

Inherited Class K-21

The PRR inherited twelve "Pacific" locomotives when the railroad absorbed the Vandalia Line, in 1917. These ALCO built 4-6-2 locomotives weighed 263,000 pounds and had 80" drivers, 24 x 26 cylinders, a 200 psi boiler pressure and they exerted 31,824 lbs of tractive effort.

On the Vandalia, they were Class VK1, road numbers 1 through 12 and on the PRR they were designated as Class K-21 and were assigned road numbers 8701 through 8712.


The Last PRR "Pacifics", Class K-5

Could the K-4s be made better? To answer that question, two very large experimental "Pacifics" rolled on to the roster in 1929, a year after the last K-4s was built. They were designated as Class K-5 and assigned road numbers 5698 and 5699. Number 5698 was built at the Altoona Works and was outshopped in April, 1929. It had piston valves, Walschaert valve gear and a one piece, cast steel frame. Number 5699 was built by the Baldwin Locomotive Works and was delivered in March, 1929. It had Poppet valves, Caprotti valve gear and a fabricated frame. These locomotives had 80" drivers, 27 x 30 cylinders, a 250 psi boiler pressure and weighed 327,560 pounds. Number 5698 had a tractive effort of 54,675 lbs and 5699 exerted 58,092 lbs.

The two K-5 locomotives were assigned to haul Philadelphia - Pittsburgh passenger trains and after electrification were assigned to the North Central line between Harrisburg and Baltimore.

By the time these locomotives were completely tested and evaluated the state-of-the-art had moved beyond the 4-6-2 wheel arrangement and the "Mountains" 4-8-2 were beginning to arrive and they incorporated many of the features tested in the K-5 locomotives.

Number 5698 was dropped from the roster in October, 1952 and 5699 was retired in September, 1953.


PRR Roster of "Pacific" Type Locomotives

ClassQtyRoad NumbersYear BuiltBuilder
K-28323, 77, 150, 163, 247, 347, 382, 397, 482, 654, 732, 821, 838, 927, 997, 1061, 1119, 1184, 1246, 1253, 1396, 1458, 1525, 2125, 2437, 2980, 3250, 3251, 3320 through 3327, 6621, 6625, 7048, 7114, 7137, 7153, 7175, 7202, 7510 through 7528, 8635 through 8644, 9990 through 99991910PRR
K-270748, 922, 1088, 1245, 3328 through 3338, 3344 through 3370, 3372, 3373, 3374, 3376 through 3394, 5035, 5060, 5107, 5130, 5133, 51911911PRR
K-2b23371 & 33751911PRR
K-2a386, 238 & 8771911PRR
K-2a52170, 196, 849, 1372, 1628, 1630, 1635, 3402 through 3411, 4096, 5014, 5039, 5078, 5087, 5097, 5112, 5183, 5212, 5214, 5221, 5223, 6064, 6084, 6085, 7170, 7177, 7182, 7183, 7211, 7217, 7219, 7224, 7271, 7272, 7316, 7319, 7327, 8077, 8111, 8395, 8528, 8529, 8541, 85431912PRR
K-2a107018, 7039, 7049, 7070, 7142, 7166, 7167, 8004, 8018, 80451912ALCO
K-2a7758, 1266, 1277, 1301, 1346, 1350, 13871913PRR
K-3s307004, 7012, 7075, 7079, 7149, 7161, 7187, 7301, 7308, 7337, 7546, 7547, 7548, 7549, 7791, 7792, 7793, 8091, 8154, 8232, 8238, 8391, 8656 through 86631913Baldwin
K-4s4112, 20, 43, 122, 227, 299, 358, 359, 383, 389, 422, 612, 623, 669, 719, 830, 920, 1120, 1139, 1188, 1195, 1395, 1453, 1462, 1488, 1497, 2034, 2445, 5022, 5038, 5041, 5058, 5072, 5077, 5086, 5147, 5154, 5238, 5243, 5253, 52961917PRR
K-4s1118, 16, 225, 262, 269, 295, 452, 518, 526, 646, 837, 850, 911, 945, 949, 958, 962, 1329, 1330, 1339, 1361, 1392, 1433, 1435, 1436, 1517, 1522, 1526, 1531, 1533, 1546, 1551, 1554, 1588, 1653, 1980, 1981, 1983, 1984, 1985, 2032, 2112, 2665, 2673, 2761, 3654, 3655, 3667 through 3684, 5334 through 5349, 7053, 7054, 7116, 7133, 7244, 7914, 7938, 8009, 8085, 8157, 8161, 8165, 8181, 8195, 8212, 8218, 8225, 8236, 8240, 8242, 8251, 8261, 8278, 8281, 8309, 8334, 8347, 8373, 8377, 83781918PRR
K-4s157267, 7270, 7273, 7274, 7275, 7278, 7279, 7280, 7287, 7288, 8068, 8108, 8114, 8122, 81371919PRR
K-4s503726 - 37751920PRR
K-4s573800, 3801, 3805, 3806, 3807, 3838 through 38891923PRR
K-4s505350 - 53991924PRR
K-4s755400 - 54741927Baldwin
K-4s175475 - 54911927PRR
K-4s85492 - 54991928PRR
K-21128701 - 87121911-12From the Vandalia in 1917

Surviving PRR "Pacifics"

There are two surviving PRR "Pacific", both are Class K-4s, number 1361 being restored at Steamtown National Historical Site in Scranton, PA and number 3750 which is on display at the Railroad Museum of Pennsylvania in Strasburg, PA.
Number 1361
The PRR placed number 1361 on display, in June 1957, at a site on the "Horseshoe Curve". This site was part of a tract of land the railroad leased to the City of Altoona, PA for a park, which was called Curve Park. The railroad donated the locomotive to the city and in return the city agreed to maintain and operate the park.
In 1985, the Railroad Memorial Museum had this locomotive evaluated and it was determined that it would be feasible to restore it to operating condition. The City of Altoona turned over the title to number 1361 to the Museum and in September 1985, the locomotive was moved to the Juniata Shops. A group of professionals and unpaid volunteers restored the K-4s locomotive and in April 1987, it was returned to service. During 1987 and 1988 it was used on several excursions until a main bearing and drive axle failed.

In 1988, number 1361 was returned to the Juniata Shops for assessment of the damage. At this time, the Federal Railroad Administration became more active in regulating operation of historic steam locomotives. Frequently changing regulations and the extent of the damage caused a great debate as to how to proceed with the restoration.

After raising funds, the Museum signed a contract, in 1994, with the University of Scranton and Steamtown for work to restore the locomotive. The University is to provide the project management and Steamtown is to provide shop space, equipment and labor. In the Spring of 1996, it was moved to Steamtown where work began the following year.

The work has progressed, but there is still more to do. In early 1999, the Museum needed to raise about $500,000.00 to finish the project. Donations can be made by contacting The Railroader's Memorial Museum at 814-946-0834.

Number 3750 When the PRR began to retire its steam locomotives it intended that number 1737, which was the prototype for Class K-4s, be preserved. When it was retired number 1737 was sent to Altoona where it sat idle for a number of years. When it was sent to Northumberland for restoration it was determined that it had deteriorated to the point that a complete rebuild would be necessary before it could be donated to a museum. Someone with the PRR decided that it would be too expensive and ordered it scrapped. A substitute was sought and a recently retired K-4s, number 3750, was selected and its number plate was replaced with number 1737's number plate that had been saved.

The impostor, number 1737, was sent to Northumberland where it was put into storage for ten years. In 1968, it was sent to the new Railroad Museum of Pennsylvania which was amassing its collection and it was on display in the museum's train yard when it opened in 1976.

By 1983, continued exposure to the elements had taken its toll on the locomotive and it was sadly in need of repair. In June, 1983, a crew of volunteers from an organization known as Friends of the Railroad Museum began a cosmetic refurbishment of the locomotive. After several months of work and after the new coat of Brunswick green paint had dried the locomotive was given its original number and is now on display as number 3750.

On December 18, 1987, Pennsylvania's governor Robert Casey signed a bill naming the PRR's K-4s the "Official State Locomotive". This title is applied equally to both the surviving Class K-4s locomotives, number 1361 and number 3750.


Class Details by Steve Llanso of Sweat House Media

Class K2 (Locobase 16277)

Data from Locomotive Testing Plant at Altoona, Penna, Bulletin No. 22, Comparison of Passenger Locomotives (Altoona, Pa: Pennsylvania Railroad Company, 1915), esp. 4-5.

Edson (Keystone Steam & Electric, 1974) notes that the K2 design was prepared by Fort Wayne while Altoona designed its K1. The K1 was not produced, so this was the first mass-produced Pacific acquired for the Pennsylvania and in such features as the 80" drivers and Belpaire firebox, it established the benchmarks for all the Keystone 4-6-2s to come.

Some of the subtleties of comparing efficiencies of saturated versus superheated boilers emerge in a comment 38 of the LTP's analysis cited above. "The evaporation for the saturated steam boiler K2 is the greatest," it reported. The report's explanation shed new light for Locobase when it explained that the result was "on account of the greater heat absorbing qualities of the boiler tube surrounded by water, as compared with a superheater tube surrounded by steam." ( Part 65 gives the ratio per square foot of superheater heating surface to water heating surface as between .268 to .426, the increase correlating with a growing proportion of superheater to saturated area.)

In other words, hot gases flowing through tubes gave up more heat to the surrounding water through the tubes' walls than the saturated steam flowing around superheater elements in superheater flues. Locobase wonders if the four-pass design of Schmidt Type A superheaters achieved ratios closer to even at the time the steam left for the cylinders.

Moreover, Part 143 summarized the benefits of superheating by noting that because superheating actually increased as the boiler was forced ("which would normally result in a lowering of efficency of the locomotive"). The authors summed up the superheater's role as acting "in a manner similar to a large accumulator or reservoir which gives up its energy when most needed, and at failry high efficiency."

A later finding--Part 60--notes the relatively high heating surface to grate area ratio was a factor in the "low" 15 pounds per hour per square foot (73 kg per hour per square metre) of total heating surface.

Very few of this class survived the 1930s, most being retired early in that decade.

Class K28 (Locobase 5693)

Data from "Pacific Locomotive for the Pennsylvania Lines West", The Railroad Gazette, Vol XLIII, No 9 (30 August 1907), pp. 238-240.

This was a single Lines West "Alco", but unlike the K29, which remained unique, this engine led to Pennsy's own K2 design. The grate was quite large, the piston valves relatively enormous at 16"(406 mm) diameter and 7" (279 mm) stroke, and the firebox radially stayed, but otherwise the K2s followed easily from this prototype.

Later superheated and redesignated K28s, when it had very nearly the same number of tubes and flues (200 & 30, vs 202 and 32) as the K2s.

Retirement and scrapping came in June 1933.

Class K29 (Locobase 7581)

Data from reproduction of 1913 Alco Bulletin 1016 on Richard Leonard's [] (accessed 16 June 2006). See also Locobase 3305, which discusses Locobase's suspicions about a mysterious entry in a 1921 table presented by an Alco designer.

Drury (1993) observes that "At some point Alco must have realized that even if it built an engine PRR would buy a thousand [examples] of [sic], Baldwin and Juniata would split the order." Even so, Edson (Keystone Steam & Electric, 1974) observes, the Alco K29 in many ways served as the forerunner for the K4 absent the Belpaire firebox.

This lone wolf soldiered on until 1929.

Class K2sa (Locobase 161)

Data from diagram scanned in by Robert Schoenberg of [] (viewed 11 April 2003). See also Locomotive Testing Plant at Altoona, Penna, Bulletin No. 22, Comparison of Passenger Locomotives (Altoona, Pa: Pennsylvania Railroad Company, 1915), esp. 4-5. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error.)

Edson (Keystone Steam & Electric, 1974) notes that the K2 design was prepared by Fort Wayne while Altoona designed its K1. The K1 was not produced.

Soon after the K2 entered service in 1910, Altoona began converting them to 151 K2a were converted to K2s, and the 72 K2a that were built by Alco and Altoona from 1911-1913 were soon converted to K2sa. 72 K2sa were built from 1910-1913, all but 10 (Alco) built by Juniata. All had Belpaire fireboxes, 16" (406 mm) piston valves, and the 80" drivers. Some built with Crawford underfeed mechanical stokers that later removed when tests showed that they increased coal consumption.

Locobase believes it's worth quoting from a Classic Trains forum thread on "Steam commuter locomotives" started by Dave Klepper on 20 February 2015 , at [], last accessed 14 April 2017. In the course of the discussion, Klepper offered on 23 February a blunt appraisal of the K2s considerable deficiencies. Noting that few ever were fitted with power reverse, Klepper continues: "[T]he K2 Pacific was a notoriously inefficient locomotive, both in coal and water usage and in maintanace, the latter because of heavy valve-gear needing adjustment frequently. Its Johnson bar was heavy for the engineer to control."

"rfpjohn" quickly seconded Klepper's assessment, offering further details: "The reluctance of engineers to adjust valve settings under way on K2s, out of fear of being injured by the johnson bar throwing them into the front corner of the cab, may have been one of the reasons they were so inefficient and also would be cause for excessive wear in the valve gear and valves. I have also read that the trailing trucks had a bad habit of running hot and also disassembling at speed! Not good."

(rfpjohn later reported that, pursuant to an ICC order in the late 1930s, some did get power reverse.)

While Johnson-bar wrestling matches ending in broken bones weren't unique to the K2, it's understandable that such a prospect would bother Pennsy engineers.

Tom ("ACY") weighed in with a defense of the K2 on 26 February, offering this judgement: "I've always liked the PRR K2's and K3's, even though they were the odd man out on PRR's roster. The built-up, outside bearing trailing truck and oversized valve gear hanger stood out on a road that had very few other engines with these features (the USRA's being among the very few exceptions). In spite of PRR's 20-25 year retirement practice, some of these 1910-13 engines lasted until 1949."

Tom concurs, however, with a general view of their unsuitability on commuter runs: "I don't believe they fit well into commuter service, but they were used on secondary trains for a long time. Maybe the difficulties with the reverse lever constituted a major problem in service that required frequent stops and jackrabbit starts."

Very few of this class survived the 1930s, most being retired early in that decade.

Class K3s (Locobase 162)

Data from "Completion of the Forty-Thousandth Locomotive by the Baldwin Locomotive Works," Brotherhood of Locomotive Firemen and Enginemen's Magazine, Volume 55, No 11 (November 1913), pp. 619-623. See also DeGolyer, Volume 47, pp. 185+. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error.) Works numbers were 39728-39730 in April 1913; 39764-39766, 39790-39802 in May; 39948-39954, 39993, 39995, 40000, 40074 in June 1913

Interim design between much more numerous K2 (225 built) and K4 (425 built). Intended for the Lines West routes, the K3 used the same boiler and Belpaire firebox as the K2sa. In the K3, however, the cylinder diameter grew by two inches, squaring the cylinder-stroke dimension. Arch tubes contributed 22.8 sq ft (2.12 sq m) to firebox heating surface area and relatively large 16" (406 mm) piston valves supplied steam to the cylinders. (The K4s used 12" piston valves because tests showed little loss of efficiency in reducing the size while realizing a savings in weight.) K3s also were delivered with a mechanical stoker, which apparently was acceptable west of Pittsburgh, but not in those areas ruled by Altoona.

One of the K3 engines delivered in July 1913 was Baldwin's 40,000th locomotive. Road numbers ranged from 7004 to 8663. The Pennsy sold five of the class in October 1930--works 39730, 39764, 39792, 39952-39553--to the Norfolk & Western, which operated them as class E-3 (road numbers 500-504). By that time, the cylinders were equipped with 12" piston valves.

Class K4s (Locobase 159)

Data from tables in 1930 Locomotive Cyclopedia. See also DeGolyer, Volume 77, pp. 464+; and C D Young, Locomotive Testing Plant at Altoona, Penna, Bulletin No. 22, Comparison of Passenger Locomotives (Altoona, Pa: Pennsylvania Railroad Company, 1915), passim. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error.)

Perhaps the archetypal 20th Century PRR locomotive, this design shared its boiler and firebox layout with the L-1 2-8-2s that appeared at the same time. See Locobase 32 -- the L1s entry -- for a comment on the unique design of Pennsy's Belpaire firebox.

425 K-4s entered service -- 350 constructed at Juniata and 75 at Baldwin. 1924-1928 locomotives numbered from 5350 to 5499, the Baldwin locos numbering 5400 to 5474. The Baldwin batch engine weight was 308,890 lb (140,110 kg) . The piston load per pound of reciprocating parts was 87 lb (39.5 kg), according to Railway Age (21 July 1916), which was 4.8% more than the E6 Atlantics, and 10.1% more than the Reading Pacifics.

The K-4 prototype generated 3,184 hp for 60 minutes running at 200-240 rpm (48-57 mph) and 60% cut-off. Other tests showed 1,275 indicated HP at 67 mph at 15% cut-off, 2,355 hp at 35% cut-off. Robert Tufnell (The Illustrated Encyclopedia of Railway Locomotives (London: Quarto Publishing Ltd, 1986)) notes that at the most efficient steaming rate of 34,000 lb (15,422 kg)/hour, boiler efficiency was 76% and the engine burned fuel at the rate of 1.8 lb/ihp/hour (5,800 lb/hour).

See Locobases 161 and 16277 for extended discussions of superheater versus saturated boiler performance.

As with most Pennsy locomotives, the K-4 had a Belpaire firebox. (See Locobase 32 for a comment on the unique design of Pennsy's Belpaire firebox.) Direct heating surface area in the Baldwins included 62 sq ft (5.75 sq m) in the combustion chamber and 34.6 sq ft (3.2 sq m) in four arch tubes. Results of earlier tests at the Locomotive Testing Plant appear to dictated the boiler-grate, cylinder size, and tube length proportions, as they are essentially as prescribed in the conclusions of the test report.

Piston valves measured a relatively slender 12" (306 mm) in diameter, following the LTPs conclusion on page 131 that tests showed that reducing the diameter from the K2s and K3s cylinders' 16" would not cost them performance and would "secure the advantage of a uniform valve diameter and [a] reduction in weight."

Power reversing gear was fitted to the class in the 1920s and most received a mechanical stoker in the 1930s.

Sources differ on the size of the superheater with a couple of the diagrams reproduced by Schoenberg noting areas of 1,072 and 1,157 sq ft. But the majority of diagrams from all periods of K-4 service show the 943 sq ft (305 sq ft of firebox area) recorded in the specs.

The tender weight represents the larger tender. Smaller ones held 7,250 gallons of water and 13 1/2 tons of coal. Most K4s were hand-fired, which is often highlighted as backward thinking. See, however, John W Orr's excellent account of an engineer on the Pennsy (Set Up Running, published by PSU Press in 2001) in which he describes on pp. 116-117 the "bank-firing" technique used by a fireman on a K4. After laying the bed in an orthodox pattern, the fireman piled large amounts of coal, "especially in the corners", but left a bright fire in the middle. Stoking the fire during the K4s high-speed runs consisted of placing a few shovelsful of new coal in the bright fire patch, which kept the pressure at near pop-off point.

Class K5 (Locobase 160)

Data from the 1930 Locomotive Cyclopedia tables. See also DeGolyer, Volume 81, 113+ for the Caprotti. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error.)

5698 was built by Juniata with Walschaerts valve gear; called the General Butler. 5699 built by Baldwin with Caprotti poppet valve gear and called the Mussolini (because of its "Italian" valve gear). Both were fitted with a Worthington "PRR" Special Type S feedwater heater.

These were hand-bombers with a GDF that suggests the Herculean task facing the fireman. See Locobase 159 for a description of the "bank-firing" technique that saved the shoveller's back. The Caprotti gear on 5699 was later replaced by Walschaerts radial valve gear.

Not considered a success.

Class VK1 / K21s (Locobase 7587)

Data from reproduction of 1913 Alco Bulletin 1016 on Richard Leonard's [] (accessed 16 June 2006). Edson's Keystone Steam & Electric (1974) shows that the class came in 3 batches: works# 47737-47740 in August 1910, 50631-50634 in February 1912, and 53971-53974 in July 1913

According to the notes in Bob Berkey's PRR Steam Locomotive Classification, the specs for these Indiana engines were similar to the Pennsy's K-2 and K-3 designs, but they were lighter, used a radial-stay firebox, and a different kind of trailing truck. They had 14" diameter piston valves. The first group was delivered with saturated boilers containing 383 2" tubes.

The Pennsy took them over in 1917 and scrapped them from December 1929-August 1930. One suspects the short lifetime is attributable to the relatively modest power dimensions and the small number of engines. This assessment is reinforced by an October 1910 account in Railway & Locomotive Engineering (p. 382) that emphasizes the easy gradients and wide-sweeping curves over which the Vandalia's trains had to travel. Perhaps when it came time to put them to more demanding use, the railroad found these locomotives would not serve.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID16,277 5693 7581 161 162
RailroadPennsylvania (PRR)Pennsylvania (PRR)Pennsylvania (PRR)Pennsylvania (PRR)Pennsylvania (PRR)
Number in Class2961129630
Road Numbers237067339510,0007004+
Number Built72117230
Valve GearWalschaertWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)13.83 / 4.2213.83 / 4.2213.83 / 4.2213.83 / 4.2213.83 / 4.22
Engine Wheelbase (ft / m)35.20 / 10.7335.16 / 10.7236.42 / 11.1035.20 / 10.7335.21 / 10.73
Ratio of driving wheelbase to overall engine wheebase 0.39 0.39 0.38 0.39 0.39
Overall Wheelbase (engine & tender) (ft / m)70.42 / 21.4667.06 / 20.4471.48 / 21.7970.42 / 21.4678.87 / 24.04
Axle Loading (Maximum Weight per Axle) (lbs / kg)61,30057,675 / 26,16165,000 / 29,484
Weight on Drivers (lbs / kg)178,500 / 80,966183,900 / 83,416197,800 / 89,721191,000 / 86,636189,500 / 85,956
Engine Weight (lbs / kg)272,000 / 123,377272,500 / 123,604317,000 / 143,789297,000 / 134,717293,200 / 132,993
Tender Loaded Weight (lbs / kg)158,000143,800 / 65,227175,700 / 79,696170,200 / 77,202271,200 / 123,014
Total Engine and Tender Weight (lbs / kg)430,000416,300 / 188,831492,700 / 223,485467,200 / 211,919564,400 / 256,007
Tender Water Capacity (gals / ML)7000 / 26.528280 / 31.366800 / 25.7615,000 / 56.82
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)11 / 1013.50 / 12.3016.10 / 14.6024 / 21.80
Minimum weight of rail (calculated) (lb/yd / kg/m)99 / 49.50102 / 51110 / 55106 / 53105 / 52.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)80 / 203280 / 203280 / 203280 / 203280 / 2032
Boiler Pressure (psi / kPa)205 / 14.10205 / 14.10200 / 13.80205 / 14.10205 / 14.10
High Pressure Cylinders (dia x stroke) (in / mm)24" x 26" / 610x66024" x 26" / 610x66027" x 28" / 686x71124" x 26" / 610x66026" x 26" / 660x660
Tractive Effort (lbs / kg)32,620 / 14796.2032,620 / 14796.2043,376 / 19675.0532,620 / 14796.2038,283 / 17364.90
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.47 5.64 4.56 5.86 4.95
Heating Ability
Firebox Area (sq ft / m2)211.50 / 19.65205 / 19.05253 / 23.51220 / 20.45226.80 / 21.10
Grate Area (sq ft / m2)53.32 / 4.9561.86 / 5.7566.10 / 6.1455.37 / 5.1555.40 / 5.15
Evaporative Heating Surface (sq ft / m2)4439 / 412.394427 / 411.434625 / 429.833691 / 343.033680 / 342.01
Superheating Surface (sq ft / m2)988 / 91.82791 / 73.51845 / 78.53
Combined Heating Surface (sq ft / m2)4439 / 412.394427 / 411.435613 / 521.654482 / 416.544525 / 420.54
Evaporative Heating Surface/Cylinder Volume326.07325.19249.26271.13230.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation10,93112,68113,22011,35111,357
Same as above plus superheater percentage10,93112,68115,60013,39413,515
Same as above but substitute firebox area for grate area43,35842,02559,70853,21855,328
Power L111,03610,94721,24423,91321,246
Power MT408.91393.70710.34828.05741.52

Principal Dimensions by Steve Llanso of Sweat House Media
ClassK4sK5VK1 / K21s
Locobase ID159 160 7587
RailroadPennsylvania (PRR)Pennsylvania (PRR)Vandalia Line (PRR)
Number in Class425212
Road Numbers1-12 / 8701-8712
Number Built425212
Valve GearWalschaertvariousWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)13.83 / 4.2213.83 / 4.2213.83 / 4.22
Engine Wheelbase (ft / m)36.17 / 11.0236.87 / 11.2434.71 / 10.58
Ratio of driving wheelbase to overall engine wheebase 0.38 0.38 0.40
Overall Wheelbase (engine & tender) (ft / m)74.67 / 22.7665.85 / 20.07
Axle Loading (Maximum Weight per Axle) (lbs / kg)65,000 / 29,484
Weight on Drivers (lbs / kg)199,500 / 90,492207,675 / 94,200165,000 / 74,843
Engine Weight (lbs / kg)304,500 / 138,119327,560 / 148,579260,000 / 117,934
Tender Loaded Weight (lbs / kg)212,725 / 96,491248,400147,400 / 66,860
Total Engine and Tender Weight (lbs / kg)517,225 / 234,610575,960407,400 / 184,794
Tender Water Capacity (gals / ML)12,150 / 46.0213,475 / 51.047500 / 28.41
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)18 / 16.4022 / 2012 / 10.90
Minimum weight of rail (calculated) (lb/yd / kg/m)111 / 55.50115 / 57.5092 / 46
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)80 / 203280 / 203280 / 2032
Boiler Pressure (psi / kPa)205 / 14.10250 / 17.20200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)27" x 28" / 686x71127" x 30" / 686x76224" x 26" / 610x660
Tractive Effort (lbs / kg)44,460 / 20166.7458,092 / 26350.1231,824 / 14435.14
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.49 3.57 5.18
Heating Ability
Firebox Area (sq ft / m2)322.60 / 29.97305 / 28.35221 / 20.54
Grate Area (sq ft / m2)70 / 6.5070 / 6.5155.60 / 5.17
Evaporative Heating Surface (sq ft / m2)4058 / 3774285 / 398.233654 / 339.59
Superheating Surface (sq ft / m2)943 / 87.611634 / 151.86752 / 69.89
Combined Heating Surface (sq ft / m2)5001 / 464.615919 / 550.094406 / 409.48
Evaporative Heating Surface/Cylinder Volume218.70215.54268.41
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation14,35017,50011,120
Same as above plus superheater percentage17,07722,40013,010
Same as above but substitute firebox area for grate area78,69897,60051,714
Power L120,85634,39922,579
Power MT691.421095.51905.06

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