Class I1s Type A (Locobase 5153)

William D. Edson (Keystone Steam & Electric, 1974) adds that these engines also had "[a] Belpaire boiler, [mechanical] stoker, Worthington feedwater heater, power reverse gear, heat-treated steel reciprocating parts, and underhung crossheads." Of the five sets of drivers, only the first and last had flanges, which reduced the design's minimum curve radius. See Locobase 32 for a comment on the unique design of Pennsy's Belpaire firebox.

Pennsy built the first 123 at their Juniata shops in 1916 and 1918-1919; Baldwin delivered 475 more in 1922-1923. Never very stylish, these were brute-force engines serving wherever there was a long train and a steep grade.

Alco Estimating Engineer James Partington (in Railway Age, 5 Nov 1921) comments that the secret to the I-1's great success lay in setting the proportions to allow for limited cutoff operation. Continuous high tractive effort levels on the long uphill runs were achieved by using a long stroke and large cylinders, but cutting off the steam at 50% of the stroke rather than the more usual 90%. "The expected increase in economy of coal and water," Partington observed, "...has been fully realized. Not only has the engine shown remarkable efficiency, but the economy under wide ranges of load is especially remarkable [sic]."

As a reminder of what "efficiency" consisted of in the steam era, note that the I-1 achieved a maximum of 8.1% thermal efficiency (generating 1,777 ihp), and averaged over 7%. Maximum IHP came to 3,080 (at 40% cutoff and 2.9 lb of coal per IHP hour.)

Class I1s Type E (Locobase 67)

Firebox had combustion chamber, boiler had type E superheater; cylinders had limited cutoff (see below). Unusually "square" tube and flue arrangment (usually engines of that era had many more tubes than flues). William D. Edson (1974) adds that these engines also had "[a] Belpaire boiler, [mechanical] stoker, Worthington feedwater heater, power reverse gear, heat-treated steel reciprocating parts, and underhung crossheads." Of the five sets of drivers, only the first and last had flanges, which reduced the design's minimum curve radius. See Locobase 32 for a comment on the unique design of Pennsy's Belpaire firebox.

Baldwin delivered these 475 in 1922-1923.

Alco Estimating Engineer James Partington (in Railway Age, 5 Nov 1921) comments that the secret to the I-1's great success lay in setting the proportions to allow for limited cutoff operation. Continuous high tractive effort levels on the long uphill runs were achieved by using a long stroke and large cylinders, but cutting off the steam at 50% of the stroke rather than the more usual 90%. "The expected increase in economy of coal and water," Partington observed, "...has been fully realized. Not only has the engine shown remarkable efficiency, but the economy under wide ranges of load is especially remarkable [sic]."

As a reminder of what "efficiency" consisted of in the steam era, note that the I-1 achieved a maximum of 8.1% thermal efficiency (generating 1,777 ihp), and averaged over 7%. Maximum IHP came to 3,080 (at 40% cutoff and 2.9 lb of coal per IHP hour.)