35640 Avenue F, Yucaipa, California 92399
My informative article, ‘The Walschaerts & The
Radials’ as published in the Jan-Feb issue of this grand
magazine was certainly intended to offend no one’s feelings who
has a penchant for the Walschaerts valve gear. I entertain warm
nostalgia for it from having worked with it in practice and of
course realize that it did bridge a long span in locomotive
engineering. While it was nonetheless imperfect, so was about every
other facet of the dear old Iron Horse. Nor could I have imagined
that this rectifying treatise would even set one reader off into
delirious tantrums. However, in the Nov-Dec edition of IMA a Doctor
of the French Horn has seen fit to not only attempt to disprove
certain remarks (which were actually quoted as attributable to
other sources) and thereby revealed his own misconceptions in these
matters, but he also diverged into an unrelated psychiatric and
medical diagnosis of what he must consider are my personal ills, in
language of insult, innuendo, and silly parallels, etc. Whereupon
he ‘curled his tail between his legs’ so to speak, and
sulked off into a corner with the protective utterance that he
wished to discuss the matter no further. In a person-to-person
manner, such complexes can be ignored or shrugged off; but the harm
here is passing on such misinformation to other unwary readers.
This recalls one philosopher’s observance, ‘A little
knowledge can be a dangerous thing.’ But the process of
learning involves a rational meeting of minds; and this must be
pursued in a logical (and at least gentlemanly) manner if any good
is to accrue. I must admit to still be learning, and it must be a
pretty dull wit who cannot learn something new every day of his
life. So let us attempt to correct what is wrong with the
Doctor’s missive, and add punctilious information which may be
of further interest in clearing up this discussion.
(1) In his third paragraph he states, ‘In the more powerful
locomotives the increased diameter of the boiler barrel left no
room underneath for the necessarily larger four eccentrics that
would be required, including the rest of the Stephenson valve
gear.’ Now, anyone who has been around the biggest and smallest
of locomotives (and those who have not can verify by scale drawings
released by manufacturers and published in various encyclopedias)
knows and can see that the exact opposite is the case. In small
locomotives, the barrels were slung low partially between the
wheels, even including firebox sections. In large locomotives the
barrels were too large to sling between the wheels, so they were
placed well atop. In the case of the most powerful two-cylindered
lokies (the Pennsylvania Decapods with over 105,000 pounds
attractive effort) even the firebox sections were over the driving
wheel contours. And since the wheels were much larger on the big
engines, there was also more clearance to ground underneath. Two of
these engines in tandem would more than equal any Mallet. And the
biggest two-cylindered engines utilizing trailing trucks under the
firebox sections (the Santa Fe 3700 and 3800 class) maintained
their boiler barrel sections at comparative wheel contour, while
having much higher driving wheels. A supervisor of mine once
disgustingly exclaimed, during an impatient interval of instruction
to one of his co-workers, ‘That should be obvious to an
idiot!’ However, I believe that such explosions tend to quash
any further questioning and thus impede the learning progress. So
it still stands, the change was for accessibility and reduced
maintenance wherever design could afford. It would have become an
absolute necessity to move to an outside valve gear in any case
about 1930, however, when Timken introduced anti-friction roller
bearings to main journals and other bearings of steam locomotives.
For the new bearing housings extended from driver-cheek to
driver-cheek and left no access to main axles. It contained the
lubricating oil and pump circulating mechanism and was very
massive. These bearings were so finely made that, in the wrecking
yard, I have rocked the housings about the axle with the fingers of
one hand, albeit it weighed over one ton. Before leaving this
correction, it is called to attention that some of Walschaerts’
early gears were driven by inside eccentric.
(2) A small detail of correction is that the original family
name in Mechlin Belgium was spelled terminating in ‘s’.
Reference the Belgian government patent papers as signed off.
Somewhere a-long the way it has often come to be misspelled without
the ‘s’ on the end.
(3) In the sixth paragraph of the Doctor’s discourse, it is
indicated that ‘The mechanism is entirely different from the
general run of valve gears in that the resultant motion of the
valve is due to two independent component motions- – -.’
However, this applies to all other types of single-eccentric
locomotive valve gears such as Baker, Southern, Young, etc., the
Young being a takeoff of the Walschaerts and also not a radial type
gear. In threshing engines utilizing radial gears, the conjugate
drive was taken off the eccentric strap at a point between the open
and closed circle drives, as mentioned later herein; this obviated
use of the combination lever.
(4) It should be pointed out in paragraph six of the
Doctor’s article that when the Stephenson motion is shifted in
cutoff or from forward to reverse, the link is actually rotated
several degrees around the shaft, with or against the fixed
eccentric settings, thus affecting the angle of advance. This
occurs by other mechanical means with outside gears; however the
lead is not changed in the latter case. This is evident upon
studying the enclosed Sketch 1. This is one graphical
representation of how a desired valve drive D of, say, 120 degrees
is obtained from an eccentric crank position (driving the yoke) at
B, being 90 degrees out of phase with the propulsion crank along
line A-C. The crosshead may be assumed to be in line at C in this
case, where the conjugate drive is taken off. By extending vectors
A-B and A-D to span the 120 degrees, and then dropping a vertical
from D to A-C to close the parallelogram, we can determine the
proportional drive displacement for each of the driving forces. In
this instance, we can scale it off as requiring 7/12 as much drive
from the combination lever as from the radius rod from the rocker
yoke. Now, suppose we ‘hook up’ the motion to gear. A-C is
fixed, of course; but A-B is reduced by half to the point projected
at E. Here it is seen that the combination link still furnishes 7
units of drive, but the yoke drive is reduced to 6 units. Also note
that the conjugate drive angle has been increased to 140 degrees.
Then why does this not increase the lead?
Because the valve travel has been shortened and the travel is
along the line DC which is constant. Thus we see that if the
Johnson Bar is placed on center, A-B becomes zero and all the drive
is loaded upon the combination link and becomes in phase with the
piston through the crosshead takeoff (or 180 degrees out of phase,
depending upon how the combination lever is connected). The same
holds when the gear is placed in reverse, with yoke drive at B-B
(180 degrees out of former phase) and the combination lever still
connected to the same position on the crosshead. Thus we see that
the yoke of the Walschaerts gear simply functions to vary the
travel from a single, simple eccentric. There is nothing radial
about it. But being a single eccentric and necessarily displaced
from the main crank by 90 degrees as described in my original
article, it requires the vector resultant action of the cross-head
and combination lever to attain the desired intermediary degrees
phase shift.
(5) In the same paragraph noted above, slip is associated with
only the Stephenson gear. However, this slip (and slop) is inherent
in any yoke and block type of gear. This is revealed in the
enclosed Sketch II which is rather self-explanatory as an outline
drawing (not to scale but nevertheless effective) of a Walschaerts
gear. The nomenclature shown is as follows:
JReach rod to Johnson Bar (reverse lever/cutoff control)
A Bell crank for suspension control
B Suspension link
K Radius rod to conjugate joint
Y Rocker (yoke)
C Sliding block (not detailed)
E Eccentric crank strap or connecting rod
L Combination lever
K Linkage to crosshead
V Valve stem extension guide
R Arc of travel for joint of suspension link and radius rod.
S Arc for correct travel of block in yoke.
X Error in valve motion introduced by projection of arc R over arc
S, requiring block to slip up and down in yoke twice per yoke
oscillation. This is why design engineers term the gear
‘sloppy’. Note also that when in lower gear, this error is
minimized but never cancelled. In road engines the lower position
is preferable for ‘ahead’ operation, but it is not always
accomplished.
The lower portion of Sketch II illustrates an adaptation of the
Scotch Yoke principle which divides the sloppiness equally between
upper and lower operating positions and therefore minimizes the
maximum shown above. This guide introduced another sliding joint
with its added cost and maintenance, however, and was not widely
utilized.
(6) In paragraph seven, it is stated that ‘— the valve
stem is connected at the top, or near the top, of the lap-and-lead
lever.’ This is ambiguous and in the first instance is
passe’ since that applies to outside admission valves, and such
piston valves went out with hat valves for the following reasons:
(a) It was desirable to relieve the valve stem packing from live
steam pressure; (b) in the culminating design of super-heater type
locomotives the steam pipes were brought down outside the smoke box
to the valve chamber, and it was advantageous to continue them into
a central single inside-admission valve configuration. Consequently
it will be found that the valve rod connects to the intermediary of
the three points of connection on the combination lever.
(7) In the same above paragraph it is (vehemently, with
another exclamation point?) stated that Walschaerts use became
‘- – – an exclusive necessity and an absolute requirement- –
-.’ Well, good gosh! How far out can we possibly go and still
call it railroading? A Mallet is simply two sets of engines in
tandem, and single units have been built which are larger than any
set of either pair thrown under a Mallet as mentioned earlier in
this rebuttal. And if there is any doubt that any other gear will
handle the biggest engines, look back at some of the Pennsy’s
stable. Further, measurements of power required to drive the valves
on a 3500 horsepower pair of cylinders reveal that at load and
speed this amounts to approximately seven horsepower. Even a
Stephenson gear could accommodate that demand. Pennsy’s Eddy
stone Shops probably conducted more testing of steam locomotives
(and did more experimenting) than any other manufacturer in this
country. They even gave turbines a whirl. It appears that our
friend Baker and other breakthrough engineers simply came on the
scene too late to buck the inertia of the heavy tide.
Upon beginning reading paragraph eleven of the Doctor’s
article, I at once went in to examine my typewriter desk to
ascertain whether there might have remained any heel marks
resulting from my beating the top of the desk with my shoes. No
marks; no vehemence. As Friday said, ‘Only the facts, man, only
the facts.’ I am just firm in my statement of truths, and used
but one exclamation point by way of quotation.
(8) Further on in the above paragraph is quoted Prof.
Furman’s definition of a radial valve gear as deriving its
motion ‘from a vibrating link or rod.’ Well,
double-de-goshis the Professor from Plunk-a-Dunk or who is kidding
whom? This by itself would include the Stephenson gear which
derives motion from a vibrating link, nothing less. Can there then
be any other than a radial valve gear? Even a plain indirect
eccentric gear, doubtless. This definition appears as of only first
indenture and is therefore out of place. The analysis of criteria
for valve gears goes somewhat as follows: First Indenture, primary
requirements for mechanical motion (rotary, oscillating,
reciprocating, etc.); Second Indenture, non-reversing and reversing
and cutoff requirements; Third Indenture, methods (eccentrics,
links, cams, etc.); Fourth Indenture, rotaries, poppets, slide,
etc.; Fifth Indenture, detail of types, radial, non-radial,
etc.
Of course one may formulate his own definition of a radial valve
gear, but he should keep his sense of geometry sharp enough to make
it definitively precise to that type of operation. Try the one
prescribed by Frank D. Graham, B.S., M.S., M.E. Princeton
University and Stevens Institute: ‘- – – the motion of the
valve is taken from some (second) point in a vibrating rod, one end
(first point) of which moves in a closed curve, while a third point
on the rod moves in a straight line or open curve.’ I have
supplied the parenthetical terms for simplification, but they do
not change the meaning which excludes the Walschaerts and
Stephenson, amongst others. Possibly Prof. Furman omitted the
second and third requirements expressed in this definition.
Now the Baker as a more modern gear, possesses two distinct
advantages over the Walschaerts gear. First, it is an all-wrist
motion and can be fitted with anti-friction bearings throughout,
which may in turn be lifetime lubricated and sealed against
contaminants. Second, it, like other radial gears, is designed to
provide much faster opening and closing of valves, thus reducing
wire-drawing of steam. Thermodynamically, this means elimination or
reduction of the wasteful condition resulting from passing a small
amount of steam over the edge of the valve and port at a volumetric
rate which is less than that due to the volume expansion in the
cylinder as the piston proceeds on its stroke. Wiredrawing is at
its worst with a comparatively slow-acting simple eccentric
gear.
The Young gear has been mentioned, and this is an interesting
close brother to the Walschaerts, and stated to be a modification
of the Deely gear in England and the Stevart gear in Belgium. It
requires a pair of cylinders (with cranks at 90 degrees) to
operate, much like a duplex steam pump. There being no eccentric
cranks, all primary and conjugate drive is taken off the
crossheads. A rocking yoke is employed, and driven at the lower end
from the crosshead on the same side. Another linkage at the top of
the yoke goes to the conjugate joint, while the block may then
drive the opposite side radius arm through a cross shaft. The good
old C & N W where I was employed in my younger days had
locomotives with Stephenson, Baker, Walschaerts, and Young gears.
Quite the gamut.
Now I have saved one of the jucier morsels until last; however,
I do have more of them in my files. No doubt most readers are aware
of the fact that Baldwin is the oldest locomotive manufacturer in
this country still doing business at the old stand under the same
name (but now amalgamated with Lima Locomotive, another superlative
builder, and Hamilton Industrial Corporation, builder of some of
the largest Diesel engines in this country). Well, at hand are
words from one of the last real authoritative locomotive steam
engineering design men of the Baldwin section, under date of 1971,
which among other things states ‘Neither (the Walschaerts nor
the Young) is classed as a radial gear.’ Again, my parenthesis,
since this was the topic of our discussion. Names can be furnished,
if necessary, to quieten anyone’s credulity.
At this point, and reviewing paragraph thirteen of the
Doctor’s treatise, it must be evident to any of our readers
that, YES, INDEED, we can imagine a big Mallet with any sort of
wheel arrangement, excepting windmills, as being set up and
operated very satisfactorily with any one of several other types of
external valve gears than a Walschaerts. No quarrel with the
latter, mind you, for it will get the engine there and back in good
shape. But if steam locomotive building had continued on into
further improvements likely we may have seen none of the valve
gears as were employed during the past fifty years. The
steamer’s availability, maintenance, and operating expense
could not compete with the Diesel or the Electric. Some of the
largest modern steamers were scrapped after only four years of
service rather than the usual forty! General Motors guaranteed that
their Diesel savings would offset the original Diesel cost of
several times that of the steamer and difference in upkeep to such
extent that the new steamers could be sold for scrap. And this
turned out to be the case, sad as it may seem. Looking back, there
was nothing else that could have done the job so effectively (and
affectionately) as the old steamer. Its romance and spectacularity
are gone.
Now, in closing this rebuttal, let me add that we out West are a
very hospitable bunch. We are noted for it. If even the good Doctor
will take a visit out here we will strive to teach him a thing or
two, and see that he enjoys the treatment in the meantime. All he
need do is cast out any hallucinations concerning imagined
adversaries stumbling around in a fog. We are not trying to tear
him down, but simply keep him on the track. And we are a pretty
smart bunch of cookies; we can take it and we can dish it out.
Don’t forget, most of us graduated from some places back there.
And if he brings his horn along, I will guarantee to make available
a guest seat on one of our symphonies. I might even be able to
arrange a short little seminar with TRW Systems treating of modern
high-pressure gauges; you know, the variety that is good up to
50,000 p.s.i.
If I appear a bit exalted in my writing, perchance it may
be excusable. It is never intended to be initially offensive. After
all, I was a simple farm boy who made it all the way from
Horsepower (Hay, so to speak) to Space; having just retired from
the USAF Minute-man Program in top echelon for depot tooling where
all testing equipment must be an order of magnitude more precise
than anything used on the Missile. The Minuteman involves every
known facet of engineering technology known to man, in the most
advanced scientific sense of the word. And the Missile did save the
United States of A during those very dark days of the early
1960’s, make no mistake about that!
