Re: Mallets

jje corporation <zephyr03@...>

Nelson Kennedy wrote:

From: Nelson Kennedy <>

At 21:51 28/04/99 -0700, you wrote:
From: "Stefan" <>

This is why SP's big AC's were "articulated consolidations" as opposed to
true Mallets, which reuse the steam for the second set of drivers, correct?
Yep, that's how a compound works. High pressure from the boiler to one
engine and the exhausted lower pressue to the other. That raises a
question for me - how did the loco deal with any imbalance of supply from
one set of cylinders to the other? Were they designed so there would
always be a surplus of steam from the exhausts of the high pressure
cylinders with any excess being vented to the atmosphere once the inlet
valve had closed?
Volume/pressure is self-regulating. In the original design, the
high-pressure and low-pressure cylinders are made to proportions which
will represent the desired match - usually half the pressure in the l-p
system as in the h-p, but if there were an imbalance, the actual working
pressure in the l-ps would simply rise or drop to equalize with the
volume . . . no problem.

Were the Garratts classified as simple articulateds as well?
Like Nelson, I can't recall an instance of a compound Garrett . . . I'm
not sure about Fairlies, though (the ones which were two complete
engine/boiler assemblies joined at a single cab with single controls) I
seem to recall seeing one with mismatched cylinders but can't remember

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