The Garrat is effectively a 'tank locomotive' whereas the US Mallets,
(excluding the Triplex) are 'tender locomotives'. The same problem of
reducing tractive effort occurs with almost every tank locomotive ever
in operation. Simply moving the boiler/engine unit pivots outwards and
placing the supplies in a seperate tender would solve that "problem".
The Triplex Mallet had the same problem, but in that case it really
would have been a problem as all the loss of weight was from just one
Well, no, had circumstances differed, the triplex *might* have
demonstrated that problem eventually, but since the inadequate boiler
never could supply enough steam for sustained running anyway, that
difficulty rarely -if ever- arose.
Whatever the boiler's failings, assuming it could raise enough pressure
to slip the drivers on starting, the major change in weight on the tender
driving wheels would have created traction problems with that group.
If I remember rightly, the main frame drivers cylinders feed the two outer
pairs of cylinders in compound form. If the rear driver set lacked weight
then either those drivers would slip, causing a drop in the mid pressure
receiver, which would effectively drop steam pressure to the front engine
unit and raise pressure to the main engine unit, or the maximum throttle
and cut-off would have to be kept below the rear engine's traction limit.
Well, but let's just assume these steam engines were used just for
helping to push trains up a ramp. There is a yard with service
facilities at the bottom of the ramp and after pushing the train up
these locos just "drift" back down or probably help a down train by
supplying additional brakes and air...
In that scenario, the boiler gets re-filled below, so the adhesion is
good while pushing up and it doesn't matter for the downhill part, anyway.
So, while it is a very limited use, such locomotives may actually work
in this scenario. AFAIK the triplex locos (2-8-8-8-2) were used by
Virginian in such a way.
A good point. However, the power trains (engines) would always be more or
less well balanced, which is a great deal more than could be be said for
some Mallets which were woefully ill balanced. I think that I am correct
in saying one or two were very nearly unusable because of that and had to
be modified or abandoned. My memory is rather shaky here. Perhaps someone
else can shed further light on the aspect of well balanced Mallets, or
Oh! I just happened to thumb through a copy of Train Shed Encyclopedia to
check a point and, referring to an earlier comment I made, I note the
Allegheny H8's were designed for 60 mph max. and 30-35 max. continuous
power output. Why then run them for long periods, or any other locomotive,
at crawling speed - it just doesn't make sense
Back when the USRA designs were done, there wasn't much interest in really
high speed for freight trains - cars had friction bearings on the axles as
well as the locos - so the need for a good balancing of the drivers really
hadn't become critical. It wasn't later till some of the western roads
wanted to get their trains over the track faster that the latest techniques
weree applied to dynamically balance freight haulers.
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
I think that we are at cross purposes, maybe?
I was talking about balanced power distribution to individual engines
related to balanced weight distribution of the boiler/main frames to
achieve equalised traction without slippage, particularly on Mallets
where, if my memory serves me correctly, some locomotives were notoriously
poor in this regard. I should have made my point clearer!
I think that you are talking about wheel balancing, yes?
Looks like it.
Mallets had the problems you're speaking of not so much because of
unbalanced weight distribution, but because the low-pressure cylinders
on the front engines had to be much larger in diameter than the high-
pressure rear cylinders, and figuring out just *how* much larger in
those days was largely (pun intended) a matter of cut-and-try to see
If you guessed wrong in the design phase, the front cylinders might
well have more (or less) thrust than you intended them to, and would
pull harder than the rear engine as a result; breaking traction every
time the front engine (A) hit slippery track (which it would hit
first, remember), (B) started up a steep grade where there was now
less weight on the front engine due to weight-transfer, or, (C) the
steam lines running from the rear cylinders to the front ones
developed leaks (and they did), in which case the front engine might
pull so poorly that the rear engine was the one that kept slipping.
As you can see, most of these problems could be (and were) solved by
using simple articulation -where all the cylinders use the same high-
pressure steam- and by increasing the sophistication of the
locomotive's articulated suspension system as well.
In an interesting and little-known sidelight; the Southern Pacific's
cab-forwards had a built-in advantage in the weight-transfer
department: where a normally oriented articulated would *lose* weight
on the pivoting driver set as the locomotive climbed a grade -possibly
causing a loss of traction- the pivoting set on cab-forwards actually
*gained* more traction on grades, which explains why these locos had
such an outstanding reputation for not slipping.
Speaking of cab-forwards: in retrospect, with 20-20 hindsight, that
design makes *so* much more sense than the traditional cab-behind one
(including the weight advantage you mentioned). Makes me wonder,
naively, why it wasn't adopted much earlier and universally. Why was a
clearly inferior arrangement taken as "the way it must be done"? Why
force the engine driver to control a huge locomotive with its train from
a vantage point with limited sight, as if peering through a small peephole?
(As a further tangent, it always cracks me up to think of all those
letter "F"s painted on early diesel locomotives, so the hidebound steam
engineers would know which way was supposed to point forwards. When was
this practice dropped?)
Found--the gene that causes belief in genetic determinism
On Thu, 03 Sep 2009 10:18:23 -0700, David Nebenzahl
Not with coal firing. Many "standard" locomotives could be supplied
for oil or coal.
There were problems with this layout though - there was at least one
fatality when oil pipes under the engine leaked causing wheel slip in
One problematic aspect of the design, however, was the routing of
the oil lines; because the firebox was located ahead of the driving
wheels (instead of behind them, the usual practice), oil leaks could
cause the wheels to slip. A nuisance under most conditions, it
resulted in at least one fatal accident. This occurred in 1941 when
a cab-forward with leaking steam and oil lines entered the tunnel at
Santa Susana Pass near Los Angeles. The tunnel was on a grade, and
as the slow-moving train ascended the tunnel, oil on the rails
caused the wheels to slip and spin. The train slipped backwards and
a coupler knuckle broke, separating the air line, causing an
emergency brake application and stalling the train in a tunnel that
was rapidly filling with exhaust fumes and steam. The oil dripping
on the rails and ties then ignited beneath the engine cab, killing
And I think there were crew concerns about safety in a collision. I
know there was a fatality when a cab forward hit a flat car.
Also they weren't used to a truck under the firebox that "steered" the
engine into curves instead of just carrying the weight so there were
some early problems with this.
Heck, Union Pacific steam locomotives had "UP" painted on the back of
the tender to show which way to re-rail it.
On Fri, 04 Sep 2009 05:18:23 +1200, David Nebenzahl
The Brits did it in the first decade of the 19th century :-)
It was only when Stephenson's boiler showed the (best) way that the "U"
flue boilers went out of fashion.
The Italians tried it pre-1900 with 4-6-0s (0-6-4?) and 0-10-0s (0-10-0s)
but the coal bunker beside the firebox severely limited the range.
The Germans tried blowing pulverized coal from a rear coupled tender
to the cab-forward firebox BR05 4-6-4 but the trunking tended to block up.
Cab-forwards really need to be oil fired!
Loco drivers don't really need wide vision - it only enables them to see
things like semi-trailers parked across level crossings. All they need to
see are the signals.
On Fri, 04 Sep 2009 09:15:20 +1200, Greg.Procter wrote:
Luckily for SP, they'd switched to ol by 1903, so when the Baldwin 2-8-8-2s
they got in 1908 resulted in near asphyxiation of the engine crews they
went looking for solutions and were able to go with a cab forward design.
Fascinating stuff. Thanks. But I was actually thinking about simple
Mallets rather than compound. Didn't some of these come well and truly
unstuck too (no pun intended)?
Personally, I've always thought that the Garratt was a fundamentally
sounder design, from several points of view, but I wouldn't argue the
case. I guess it's very much 'horses for courses' and there must have been
successes and failures in both camps.
Americans tend to use the word "articulated" where other countries use
Mallet because other kinds are uncommon there.
Mallet's original patent was for a compound, not the articulation
method he used.
Some of the last compound Mallets had low pressure cylinders to the
limit even of the large American loading gauge.
It's not articulated, but Churchward showed that a well designed
simple engine was just as good and a lot cheaper to build - he used
two cylinders with a very long piston stroke giving the save volume as
the de Glehn compound's four.
The de Glehn was a far smoother running engine and being a balanced
design gave negligable hammer blow due the two cylinders on each side
operating at 180 degrees to each other, balancing each other out.
So Churchward came up with simple 4-cylinder engines with the same
I've heard that.
They were certainly very good engines. Californian friends my age who
saw them in operation speak very highly of them.
It's an inherently less stable design than the Garratt which is more
like two locomotives with a boiler slung berween them rather than a
single flexible one. Garratts, Fairlies and and Meyers run more like
bogie passenger carriages.
Me too. Outside the USA it pretty well superceded the Mallet. I
suspect there might also have been patent royalties.
There were a few other kinds in the USA. The Denver and Rio Grande had
a Fairlie that was shipped out from the UK but this didn't have enough
fuel or water capacity. Mason built one double Fairlie and a lot of
single Fairlies. And don't forget the Heislers, Shays and Climaxes.
A "Mallet", by definition, *is* a compound Mallet, although simple
articulateds were also sometimes misnomered as Mallets by folks who
didn't really understand the difference. In their minds two or more
sets of drivers with a hinge in between equaled a "Mallet".
From what I've read, some early simple articulateds were indeed prone
to slipping the front engine under some circumstances, but I never
heard of them having that problem to the same extent as did compound
But the causes of loss of traction on the front engine are immediately
obvious if you look at the side elevation of practically any
articulated design: the rear engine supports much of the weight of the
cab, the firebox, and the largest diameter portion of the boiler,
while the front engine has only the lighter portion of the boiler and
the smokebox (which is hollow) above it to provide downforce. And in
most articulated designs at least the first set of drivers hang clear
out beyond the front of the smokebox!
I've never seen any figures on what the weight differential between
sets of drivers was on the various articulated designs, but it's a
safe bet to say that the less weight the front engine carried in
proportion to the rear engine the more prone it was to slip the
BTW: It was easier to slip a set of steam engine drivers than most
people suppose. In the video listed below you can see an over-
enthusiastic hand on the throttle break one set (I can't tell for sure
which set) of drivers loose under a cab-forward while it's still on
the roundhouse lead track and is barely off of the turntable! Listen
to the exhaust note suddenly speed up...
From the URL listed below: "While it is not technically correct to
call them Mallets since they are not compounds as per the Mallet
patent, simple articulateds like Weyerhaeuser #111 were identical in
design concept to a regular Mallet except for the fact that live steam
was delivered to both sets of cylinders at the same time."
What part of this did you not understand?
You don't know what sort of locos we're talking about in this portion
of the thread even after reading the URL?
If so, you need more help than I can give you.
I know perfectly well what I'm talking about.
Mallet's system of articulation is not the only kind.
What part of that did YOU not understand?
Just because there was (mostly) just one articulation system used in
the US, doesn't mean they have exclusive use of the term to mean
Mallet's articulation system.
Tell me, what would YOU call a simple engine using Mallet's
articulation system given that "articulated" does not exclusively
Articulated on its own means generic articulated.
I'm not the one who jumped in to insist that "Mallet" really meant
compound Mallet articulated.
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