As its number suggests, this is the first of one hundred and three 1050 Class Prairie type (2-6-2) locomotives built for the AT&SF by Baldwin between 1902 and 1903 (#1050-#1152). As built, #1050 was a four cylinder Vauclain compound with 17" x 28" high pressure and 28" x 28" low pressure cylinders. The engine had two pistons mounted in line and moving in parallel to drive a common crosshead. The valve was on the inside, controlled by Stephenson valve gear.
The main advantage claimed for compounding was lower fuel and water consumption, but the Vauclain arrangement produced uneven forces and excess wear at the crosshead, which increased maintenance costs and largely offset any fuel economies. The complex valve assembly and the starter valve, which allowed admission of high pressure steam directly to the low pressure cylinder, also increased maintenance costs.
By the turn of the century, many US railroads were turning away from compounds and converting those they owned
to single-expansion locomotives. The AT&SF
subsequently simplified all its 1050s between 1910 and 1922 with 23½" x 28" cylinders.