Re: [ihc] no IH content, but fun--

[bearbvd@xxxxxxxxxxxxxx (Greg Hermann)]

At 7:47 AM 10/26/04, Richard Welty wrote:
>On Mon, 25 Oct 2004 08:04:14 -0700 (PDT) Steven Stegmann
><steve.stegmann@domain.elided> wrote:
>
>
>technically, the Big Boy was not a Mallet, which was
>an earlier variantion on the articulated theme. there
>were a couple of technical features that distinguished
>the Mallet, all of which escape me now.
>
>richard
>--
True Mallets (a French development, as might be guessed from the name) used
compound expansion--had a set of small diameter cylinders on one set of
drivers and a much larger diameter set of cylinders on the second
set---which were powered by the exhaust steam from the first set of
cylinders.

While this arrangement led to greater thermal efficiency--the American
railroads found that for a given boiler area, that they could get more
drawbar pull--and get a heavy freight over a grade faster--if they simply
ran equal diameter cylinders on both sets of drivers on an articulated
locomotive, and fed high pressure steam straight from the boiler to all
four of them. Fuel efficiency be d*mned, get the train over the hill !!!

IIRC, a Big Boy would generate something like 155,000 lbs. of pull on its
drawbar from a standing stop--

Steam locomotives were NEVER a particularly efficient contraption--15%
overall heat to mechanical effort was about as good as they ever got, with
that coming on the ones that had a feed-water heater (in the form of a
round heat exchanger crossways across the front top of the boiler to grab
some waste hear from the stack)

Highest pressure steam any of them ever ran, so far as I know, was 300
psi--in the SP's 4-8-4 (Northern type) 'Yellow Jackets' that they ran on
their 'Daylights'.

Greg