The Pennsylvania Railroad

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 N1s was a class of 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...

 built for Lines West. They were of 2-10-2

2-10-2

Under the Whyte notation for the classification of steam locomotives, 2-10-2 represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle, usually in a trailing truck...

 "Santa Fe" wheel arrangement

Wheel arrangement

In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...

, ten driving wheels with a two-wheel leading truck and a two-wheel cast KW-pattern trailing truck under a giant firebox. This arrangement was well suited to the N1s' intended purpose, which was as a heavy drag freight

Drag freight

A drag freight is a slow, high-tonnage railroad train, often carrying commodities such as coal or ore. Compared to Fast freight trains, drag freight trains have a very low power-to-weight ratio, making them somewhat unpredictable on steep grades or hilly routes...

 engine for coal and iron ore traffic to and from lakeside ports. The design was developed by the PRR's Fort Wayne

Fort Wayne, Indiana

Fort Wayne is a city in the US state of Indiana and the county seat of Allen County. The population was 253,691 at the 2010 Census making it the 74th largest city in the United States and the second largest in Indiana...

 Shops and orders were placed with Alco (Brooks) (35 locomotives) and 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...

 (25 locomotives) for a total of 60; the first Alco locomotive was delivered in December 1918, with the remainder arriving during 1919.

The N1s was a large locomotive; the boiler was the largest then used on any non-experimental PRR locomotive, with a large Belpaire firebox

Belpaire firebox

The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium. It has a greater surface area at the top of the firebox, improving heat transfer and steam production...

 with 79.9 square feet (7.4 m²) of grate area and a 5 feet (1.52 m) long combustion chamber. No feedwater heater

Feedwater heater

A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system...

 was fitted, but a mechanical stoker and power reverse were, necessities on such a large locomotive. Boiler pressure was 215 pound per square inches (1.48 MPa), although it was designed to take a pressure of 250 psi (1.72 MPa).

To allow the locomotive to negotiate tight 23-degree curves, the first and fifth driving axles were fitted with lateral motion device

Lateral motion device

Lateral motion devices permit the axles in some railroad locomotives to move sideways relative to the frame.-Purpose:The coupled driving wheels on steam locomotives were held in a straight line by the locomotive's frame...

s and the center pair of drivers were blind.

In many respects, the N1s was similar in ability to the I1s

PRR I1s

The Pennsylvania Railroad's class I1s steam locomotives were the largest class of 2-10-0 "Decapods" built in the United States, with 598 built 1916–1923 . These locomotives were the premier freight locomotive type on the system until World War II, and they remained in service until the end 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...

 "Decapod". Driver diameter, weight on drivers and cylinder size were almost identical. The N1s' boiler was larger, but of a lower pressure. The I1s' 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...

 was a little higher, while the N1s had a superior factor of adhesion

Factor of adhesion

In railroad engineering, the factor of adhesion of a locomotive is the weight on the driving wheels divided by the starting tractive effort.A common rule is that for a steam locomotive a good factor of adhesion equals or exceeds 4, but not by too much...

. The N1s, as a low-speed drag hauler, was limited to 35 mph (15.6 m/s), while the I1s was capable of 50 mph (80 km/h) or greater.

The N1s were the first class of large power withdrawn after diesel locomotive

Diesel locomotive

A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...

s appeared; all were gone by 1950, and none were saved for display. Their task, low-speed drag haulage, was the diesel locomotive's forte.