"Trimming" Both Engines of a Mallet

NW Mailing List nw-mailing-list at nwhs.org
Sun Jul 24 20:59:38 EDT 2022

Early in the Mallet era it was found that the ration of piston area of the
low=pressure engine and the high-pressure was 2.5 to 1.  This allowed the
valve cutoffs of the two engines to be virtually the same as speed
increased and the cutoffs of both engines to work together very nicely.
N&W kept tinkering with its Y-class  engines and eventually come up with
differing  full-gear cutoffs of  70 percent for one engine and 75 percent
for the other; regrettably I don't recollect which was the high and which
was the low.  But Mallets worked very nicely with one power reverse
cylinder for both.
- Ed King

On Sat, Jul 23, 2022 at 2:50 PM NW Mailing List <nw-mailing-list at nwhs.org>

> Abe,
> Drawings are in the archive. As far as the linkage is concerned it is
> pretty simple. Just follow the arms and levers.. An arm from reverser is
> connected to the HP valve gear, which in turn has a crossbar which has a
> lever in the middle, which has an arm going forward to a lever on a
> crossbar of the LP valve gear.
> Jimmy Lisle
> Sent from my Verizon, Samsung Galaxy smartphone
> -------- Original message --------
> From: NW Mailing List <nw-mailing-list at nwhs.org>
> Date: 7/23/22 1:21 PM (GMT-05:00)
> To: N&W Mailing List <nw-mailing-list at nwhs.org>
> Subject: Re: "Trimming" Both Engines of a Mallet
> After two cups of morning coffee, I think I figured out part of the
> answer.
> 1.  On Compound engines, the once-expanded steam at full pressure and
> volume was probably sent forward to the front engine, so the front engine
> did not need trimming.  But it still needed reversing, and I have not
> figured that one out, yet.
> 2.  On Non-Compound engines, like the Class A articulateds, my original
> question still stands.  How was steam admission to the front cylinders
> reversed and how was it trimmed, from the single reverse bar in the cab?
> So many questions.  Life is complex.... or is it Compound ?
> -- abram burnett
> Macro-Trends Turnip Consultancy
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