PRR I1s
Encyclopedia
Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
's class I1s steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
s were the largest class of 2-10-0
2-10-0
Under the Whyte notation for the classification of steam locomotives, 2-10-0 represents the wheel arrangement of two leading wheels on one axle, ten powered and coupled driving wheels on five axles, and no trailing wheels...
"Decapods" built in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, with 598 built 1916–1923 (Altoona
Altoona Works
Altoona Works is a large railroad industrial complex in Altoona, Pennsylvania. It was built by the Pennsylvania Railroad to supply the railroad with locomotives, railroad cars and related equipment. For many years it was the largest railroad shop complex in the world.-History:In 1849, PRR...
: 123, Baldwin
Baldwin Locomotive Works
The Baldwin Locomotive Works was an American builder of railroad locomotives. It was located in Philadelphia, Pennsylvania, originally, and later in nearby Eddystone, Pennsylvania. Although the company was very successful as a producer of steam locomotives, its transition to the production of...
: 475). These locomotives were the premier freight locomotive type on the system until World War II, and they remained in service until the end of PRR steam in 1957. Nicknames for the type included Decs and Hippos, the latter due to the large boiler. Unlike smaller 2-10-0s that preceded them, the I1s design was huge, taking advantage of the PRR's heavy trackage and high allowed axle load
Axle load
The axle load of a wheeled vehicle is the total weight felt by the roadway for all wheels connected to a given axle. Viewed another way, it is the fraction of total vehicle weight resting on a given axle...
, with a wide, free-steaming boiler. Giant cylinders enabled the I1s to put down that power to the rails, and giant tenders allowed such hungry and thirsty beasts to work hard and long between stops. Their power and sheer brute force was undeniable, but they were not popular with the crews, for they were hard riding at all but low speeds. Indeed, one author described them as the holy terror of the PRR. The reason for this was that the large boiler limited the size of the driving wheels, which made it impossible to mount counterweight
Counterweight
A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...
s large enough to balance the piston thrusts.
Subclass I1sa increased maximum steam cut-off to admit steam for 78% of the piston stroke, rather than the standard 50%. This boosted low speed tractive effort
Tractive effort
As used in mechanical engineering, the term tractive force is the pulling or pushing force exerted by a vehicle on another vehicle or object. The term tractive effort is synonymous with tractive force, and is often used in railway engineering to describe the pulling or pushing capability of a...
from 90000 to 96000 lbf (400.3 to 427 kN), and raised the top speed of the locomotive from about 25 mph to 50 mph. There was no obvious external difference except for a revised builders' plate. I1s locomotives were converted to I1sa during major overhaul. 489 were converted, while 109 remained as built.
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