Class K28 (Locobase 5693)

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 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 http://www.railarchive.net/alcopacifics/index.html (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, 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 boiler.

This lone wolf soldiered on until 1929.

Class K2sa (Locobase 161)

Data from diagram scanned in by Robert Schoenberg of http://prr.railfan.net/diagrams/PRRdiagrams.html (viewed 11 April 2003).

This is an umbrella classification for several K2 classes that soon acquired identical dimensions and power. 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. Most superheated within a few years of completion. Some built with mechanical stoker (later removed).

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.

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

Class K3s (Locobase 162)

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, but the cylinder diameter grew by 2 inches, squaring the cylinder-stroke dimension. 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. N & W bought 5 K3 from the Pennsy in August 1930 and put them into service as the E-3 class 500-504; data comes from the N&W 3 1995 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Class K4s (Locobase 159)

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. The piston load per pound of reciprocating parts was 87 lb, 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. Tufnell (1986) notes that at the most efficient steaming rate of 34,000 lb/hour, boiler efficiency was 76% and the engine burned fuel at the rate of 1.8 lb/ihp/hour (5,800 lb/hour).

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.) Power reversing gear 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.

Class K5 (Locobase 160)

Data from the 1930 Locomotive Cyclopedia tables. 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). These were hand-bombers with a GDF that suggests the Herculean task facing the fireman. The Caprotti gear on 5699 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 http://www.railarchive.net/alcopacifics/index.html (accessed 16 June 2006).

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. 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.

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.