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!