04-14-2014, 08:40 AM
I happen to have the full DVD of which the clip I linked was a sample, and I went back and watched the whole thing. The guy who made the film, E.C.Eddy, appears to have been a very knowledgeable railfan with good contacts in the N&W. He says in the narration that the Y6bs worked simple up to 10 mph. Above 10 mph there was a second option, feeding reduced-pressure steam into the low-pressure cylinders directly from the boiler. It seems to me that this would also have caused a back-pressure problem from the high pressure cylinders, and some or all of the high-pressure exhaust might have had to be sent straight to the blastpipe.
The modifications for the Y6b [as originally designed, but see the post below] appear to have been unrelated to the use of steam. I don't know how far back these modifications go on the N&W Y class, or how common they may have been with other Mallets in the US.
The modifications for the Y6b [as originally designed, but see the post below] appear to have been unrelated to the use of steam. I don't know how far back these modifications go on the N&W Y class, or how common they may have been with other Mallets in the US.