Pennsylvania Railroad class N1s

The Pennsylvania Railroad (PRR) N1s was a class of 2-10-2 "Santa Fe" steam locomotives built for the Pennsylvania's Lines West. 60 engines were built between December 1918 and November 1919, and worked heavy mineral freight to and from ports on the Great Lakes until their retirement in the late 1940s. All examples were scrapped by 1950.

Overview
The 2-10-2 wheel arrangement, ten driving wheels with a two-wheel leading truck and a two-wheel cast KW-pattern trailing truck under a large Belpaire firebox, suited the N1s' intended purpose well. They were drag freight engines, designed to haul heavy freight up the 0.3% grade leading out of the PRR's "Lake ports," and were rated at 6000 tons (5443 tonnes) on these relatively easy grades. The design was developed by the PRR's Fort Wayne Shops and orders were placed with Alco (Brooks) (35 locomotives) and Baldwin (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, and the firebox had 79.9 sqft of grate area and a 5 ft long combustion chamber. No feedwater heater was fitted, but a mechanical stoker and power reverse were installed, being necessities on such a large locomotive. Boiler pressure was initially set at 205 psi, but was quickly raised to 215 psi. The boiler was reportedly designed to take a pressure of 250 psi, but whether it attained this pressure in service is not known.



To allow the locomotive to negotiate tight 22-degree curves, the first and fifth driving axles were fitted with lateral motion devices and the center axle was blind.

Comparison
In many respects, the N1s was similar to the I1s 2-10-0 "Decapod". Driver diameter was identical, and the cylinders on the I1s were a mere 0.5 in wider, having the same stroke of 32 in. The N1s had a longer boiler at 20.83 ft long, but the I1s used a higher working pressure of 250 psi. The I1s' tractive effort was higher, at just over 102000 lbf, but the N1s had a superior factor of adhesion—4.13 to the I1s' 3.28, suggesting the N1s had less of a tendency to slip than the Decapod. The N1s, as a low speed drag hauler, was limited to 35 mph, while the I1s was capable of 50 mph or greater.

Disposition
The N1s were the first class of large power withdrawn after diesel locomotives appeared, as diesels proved superior at the low-speed "lugging" the N1s was designed for. All were scrapped by 1950.