Erie class P-1

On mountain lines such as Susquehanna Hill, the Erie Railroad had the problem that the 3,500 to 5,500 ton trains, each hauled by a Consolidation or Mikado locomotive in the flat, could only be brought over the grade with difficulty. Although they already used Mallets, often two helper locomotives were necessary. With the support of George R. Henderson of Baldwin, a triplex locomotive was built, which had three groups of eight drivers each. Only the prototype was built in 1914, christened “Matt H. Shay” after a well-known railroad employee.

The six cylinders were all of the same dimensions to enable compound action with two high pressure and four low pressure cylinders. The cylinders in the middle acted as high-pressure cylinders, with the exhaust steam from the right-hand cylinder being fed into the cylinders of the front truck and the exhaust steam from the left into the cylinders on the rear truck. Only the exhaust from the front low-pressure cylinders went into the smokebox, while the rear operated a feedwater heater in the tender.

During operation, it was quickly noticed that the boiler was not producing enough steam to reach significant speeds. Although the grate on the following two locomotives of 1916 was increased from 90 to 122 square feet, they too failed to produce sufficient steam. Even the large firebox with brick arch and combustion chamber could not improve this situation. As a result, the locomotives were only used as helpers, where average speeds were barely over 10 mph. 

The powered tender also proved problematic in practical use. It offered a smaller capacity than conventional tenders of the same size because the engine took up space and increased the empty weight. When the supplies were used up, the adhesive weight of the tender also dropped so much that it quickly began to slip. Since the other driver groups were now also suddenly subject to greater loads, they quickly lost grip. Thus, their number stagnated at three and the Virginian class XA remained the only other triplex locomotive that was built. A quadruplex locomotive already planned by Henderson was never built. The three P-1 were retired in 1929, 1931 and 1933.