[N&W] Re: Garratts vs. Mallets

[nw-mailing-list at nwhs.org]

Ed-

Probably the number one reason Garratts were never tried over here was that
they were a patented, proprietary design of the Beyer-Peacock Company.  ALCO
held the U.S. license, and tried to interest some railroads in the concept
in the ~1920's, but none ever got off the drawing board.  Beyer-Peacock
promoted Garratts heavily around the world; some other companies built them
under license and other companies built un-licensed copies.

We've had the Mallets versus Garratts debate over on the "steam_tech"
mailing list several times over the last couple of years, and some good
points have been made on both sides.

In the Garratt's favor, it allows a the locomotive to have a short, fat
boiler with a wide deep firebox, which is (1) cheaper to build and (2) more
efficient for several reasons.  The two sets of running gear spread the
locomotive's weight out over a long distance, and the location of the pivots
gives the engine good riding and tracking characteristics.  The boiler
actually tracks on the inside of the curve (imagine the string on a hunting
bow) which makes the engine more stable.  Against the Garratt, you have
limited fuel and water supplies which are carried on the engines.  As these
supplies are used up, the adhesive weight changes which makes designing for
maximum tractive effort pretty tricky.  (Some Garratts used auxiliary water
tenders to minimize this problem- and adhesion was rarely a problem with any
Garratt.)  The bigger the engine, the more tricky it becomes to fit all the
various pipes and linkages to the rear engine around the firebox- steam
supply, steam exhaust, reverser linkage, air or vacuum brake lines, water
equalizer pipe (between the front and rear tanks) etc.  The longer the steam
pipes, the larger they need to be to minimize the pressure loss and the more
insulation they need to minimize the temperature drop.  The flexible joints
may have been tricky to design, but no more so than on a Mallet.  (By the
way, the pressure drop on an A's front engine appears to me to have to been
due to the tight 90 bends at the rear joints and the 180 degree turn at the
front joints- but they still had to be better than the joints on the UP
engines!)

As to previous Garratts, the largest one was built for use in Russia (a very
cold place) but it was evidently not successful, which may confirm the
condensation problems you suggest.  The highest boiler pressure used was on
some French-built 4-6-2+2-6-4 Garratts built for Algeria, which had a
pressure of 284 PSIG, so high boiler pressure wasn't out of the question.
The only compound Garratt (with HP cylinders on one unit and LP on the
other) actually built was for India, but I don't believe it was even
superheated as was not repeated.  Some Garratts were proposed (but not
actually built) which would have had 3-cylinder compound cylinders on each
engine.

Garratts are STILL operating in Zimbabwe, despite the repeated efforts of
Canadian railroad consultants to put them out to pasture for the past 20
years.  Zimbabwe (formerly Rhodesia) had completely dieselized in the 70's,
but then re-steamed in the early 80's when their oil supplies were cut off
by their neighbors.  Every engine which was returned to service was a
Garratt.  Many were fitted with roller bearings, better exhausts and larger
fuel and water capacities.  Unfortunately, as soon as oil became available,
they started retiring Garratts, but their poor financial situation makes it
hard to keep diesels in service (expensive foreign-produced parts) so their
Garratts hang on despite their best efforts to get rid of them.

I guess the bottom line in the argument is either (1) the Garratt
arrangement was especially beneficial for locomotives built for small track
gauge and light axle loadings but this wouldn't have been a big benefit in
the U.S. where these weren't problems or (2) the Garratt arrangement allowed
the biggest, most powerful steam locomotive to be built up to the limits of
loading gauge and axle load, and therefore you could have built Garratts
which were bigger and more powerful than our biggest Mallets.

Whichever argument is correct, it would have been interesting to see what
sort of Garratt the N&W could have turned out....

Good Steaming,
Hugh Odom
The Ultimate Steam Page
http://www.trainweb.org/tusp/
_____________________________________________________________
Thanks for your considered reply Ed. I appreciate that my comments were a
little contentious and I did not expect you to lay back and say "we was
wrong the limeys got it right". The UP comment was also tongue in cheek, I
do not know how far they got with the idea. In fact America made the best
of a design that was originally for a tiny French loco and the N&W designed
the best Mallet's. Similarly Beyer Peacock made the best of another design
for what was originally for a very small loco.
Just to comment on some of your points,

No Garratt was built the size of a N&W A or Y, however 5'- 3" gauge
Australian Garratt's exceeded 100,000lbs tractive effort.
300psi is about the maximum possible for fire tube boilers and though this
pressure was not used for Garratt's it is not uncommon for large stationary
boilers of similar shape (though 3 pass). Better steel quality and welding
allowed higher pressures to be used.

Your correct, flexible joints and long steam pipes are the Achilles heel of
all articulated's. Good design, lagging, high super heat temperatures.
Three cylinder compounds (one hp two lp at each end) could have been tried
though these had fallen out of favour by the 1930's.

Though the coal and water loads drop with use, all the weight in a Mallet
is in the tender where it does not help.

The Beyer Peacock patents may have been a problem, though the Germans built
export Garratt's under licence.

Garratts were used in the UK where not as cold as WV, it still gets below
freezing.

Again I agree, today we can communicate so easily, in the 1930's it was not
so easy to exchange ideas across the Atlantic.

The development of the Mallet went through some odd phases before the
ultimate class A. The Triplex, Santa Fe bendy boilers and numerous tender
booster conversions all fell by the wayside. Hind sight is a wonderful
thing, perhaps I should attempt a "what if " Garratt for the convention.

Regards, Richard Hood