PRR turbine steam use

[BobLI]

Did the PRR 6-8-6 steam turbine use about the same steam as the PRR articulated locomotives which used 4 cylinders? Or was the use larger which was why they never built another?

[rlsteam]

Reportedly, the geared steam turbine used excessive steam because there was not a very good way to get "cutoff" as with a locomotive with a valve gear. Especially at slow speeds too much steam was needed just to keep moving. Remember, steam in a locomotive with cylinders exerts power by expansion against the resistance of a piston, and the flow of fresh steam into the cylinder can be reduced and the expansion of the reduced steam still occurs. With a turbine the steam has to exert continuous pressure against the turbine blades, so there isn't the same opportunity for expansion to occur if the flow is reduced.

The PRR's only four-cylinder articulateds were a few 0-8-8-0 yard switchers, if I recall correctly. The duplexes (S-1 6-4-4-6, T-1 4-4-4-4, Q-1 4-6-4-4, Q-2 4-4-6-4) were rigid-frame, not articulated. They had their problems but certainly used steam more efficiently than the turbine.

[Allen Hazen]

The P.R.R. had a fewother articulateds, including a mammoth 2-8-8-0 which was the first Simple Articulated built (their others, 0-8-8-0 and 2-8-8-2 were Mallet compounds). I think the over-all dimensions of the 2-8-8-0's boiler may have been the largest ever on the P.R.R., but the Turbine's boiler would have had significantly larger firebox, and was probably capable of generating a larger quantity of steam.

As Richard notes, the Turbine was inefficient at low speeds: it was more economical (used less steam per horsepower hour) than conventional steam locomotives at high speeds, but less efficient than conventional steam at low speeds.

[BobLI]

Thank you for the answers.