From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: rec.railroad
Subject: Re: compound locos (was Re: High Speed Rail Query)
Date: 8 Nov 92 19:59:17 GMT
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA

In article <BROWNP.92Nov7172918@bizet.cs.unc.edu> brownp@cs.unc.edu (Peter Brown) writes:
> In article <1992Nov6.064845.19703@sq.sq.com> msb@sq.sq.com (Mark Brader) writes:
> 
> Something Mark doesn't mention about the Vauclain is that the high-
> and low-pressure cylinders also shared a common valve chest
> (presumably rather more complex than a standard valve chest);
> generally this was a piston valve (as opposed to the slide valve
> standard in American practice in the 1890's), mounted inboard of the
> high-pressure cylinder and actuated by inside valve gear.  You can see
> the front of it pretty clearly in photos of the early Vauclain
> compounds.

I think all the Vauclain design were piston valve, one of the features
was that one set of valve gear operated a single piston valve with some
extra annular rings/ports for the high and low pressure cylinders.

Around the turn of the century each manufacturer had their own compound
scheme that they favored.  Baldwin had the Vauclain compound, Brooks
had the tandem conpound scheme and everyone had a cross-compound scheme.
At this time, piston valves were new-fangled, anything beyond Stephenson
valve gear was experimental and articulated locomotives were an excercise
for the future...

For some reason the Vauclain compounds have always looked very nice -
they didn't have the ungainly appearance of the cross-compounds and were
generally applied to the fast passenger engines that were in transition
from the earlier rinky-dink 4-4-0's and 4-6-0 but still retaining a
charming simplicity of design.  Maybe it's just something about lacy
84' drivers...

    The Vauclain System

    This system of compounding is the invention of Mr Samuel M. Vauclain,
    a member of the firm of Messrs. Burnham, Williams & Co., proprietors
    of the Baldwin Locomotive Works.  The system bears the inventor's
    name.  It has both high and low-pressure cylinders on each side, the
    steam from the high-pressure cylinder exhausting into the low-pressure
    cylinder on the same side and thence out through the stack, making each
    independent of the other, with an equal pressure exerted on each side,
    one cylinder being above the other, with both pistons fastened to the
    same crosshead.  On engines that stand high above the rail, the high-
    pressure cylinder is above the low-pressure one, while on engines that
    are very low the high-pressure cylinder is placed below to clear the
    rail.

    In designing the "Vauclain" system of compound locomotives, the aim
    has been:

      1.  To product a compound locomotive of the greatest efficiency,
    with the utmost simplicity of parts and the least possible deviation
    from existing practice.  To realize the maximum economy of fuel and
    water.

      2.  To develop the same amount of power on each side of the
    locomotive, and avoid the racking of machinery resulting from uneven
    distribution of power.

      3.  To insure at least as great efficiency in every respect as in
    a single-expansion locomotive of similar weight and type.

      4.  To insure the least possible difference in cost of repairs.

      5.  To insure the least possible departure from the method of
    handling single-expansion locomotive; to apply equally to passenger
    or freight locomotives for all gauges of track, and to withstand
    the rough usage incidental to ordinary railroad service.

	-- The Locomotive up to Date, Chas. McShane 1899

The same book has an interesting discussion, too long to type in, on the
trade-offs between compound and simple locomotives, including repair costs
and other factors.  The conclusion seemed to be the compounds had the edge
at the operating condition where the multiple expansion actually worked
well (mid-cutoff, full is about the same for either scheme and short would
require a condenser to exhaust into vacuum for the low-pressure cyliders).
As has been previously pointed out, the application of superheaters broadened
the range of cutoff at which the simple engines would operate efficiently.

Multiple expansion engines were universally used for stationary and marine
applications, but the conditions there were near-constant load over a period
of hours or days and condensing exhaust.

-- 
George Robbins - now working for,     work:   to be avoided at all costs...
but no way officially representing:   uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
Commodore, Engineering Department     domain: grr@cbmvax.commodore.com