Mr. Walschaerts, Esq., and Others

| January/February 1972

  • Graphical representation

  • Slip is associated with Stephenson gear

  • Graphical representation
  • Slip is associated with Stephenson gear

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?


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