LOCOMOTIVE VALVE-GEARS COMPENDIA

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958 Sheridan Avenue Ypsilanti, Michigan 48197

Valve gears, their design, their operation and their relative efficiency have been an intriguing study and a serious problem that have eventuated into a wide variety of inventions. From the time of the building of the first locomotive, the method employed to actuate the valves that are required to supply and regulate steam from the boiler to the cylinders and discharge it after it had performed its work, were wildly experimental and mechanically crude.

About 1840 the double-eccentric hook motion had naturally evolved into a shifting-link action, under the name it has ever borne----The Stephenson Link Motion; and due to the ultra conservatism and a lack of a creative and a progressive incentive on the part of American locomotive builders, this ancient and somewhat misfit valve gear remained a vital part of all American locomotives even as late as several years of the early years of 1900.

However, to remain solvent and to be competitive in reference to new and accruing more modern methods of freight transportation, longer freight trains were essential as a matter of expediency and sound railway economics, which situation, in turn, required more powerful and larger locomotives for railway operation. 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. This fact, in conjunction with the added inertia of the heavier required parts, make it positively impossible to continue the application of the Stephenson link-motion valve gear for any further use in large locomotive construction. Thus it was the force of circumstances that triumphed over the bullheaded and dogmatic conservatism of American locomotive builders and forced the discontinuation of further applications of the Stephenson link motion valve gears on American locomotives! Due to its many years of successful operation on European locomotives, its comparatively light weight, its outside convenience for inspection and repairs, its minimal width factor and its superior steam distribution qualities; these advantageous qualities in summation, determined the consideration and the adoption of the Walschaert valve gear as the only feasible application and practical solution for the pressing locomotive valve gear problem.

The year circa 1844 was a transitional period in the development of valve gears. At this time, Egide Walschaert was Master Mechanic for the Belgian State Railways. Egide Walschaert, it seems, was very much dissatisfied with the results obtained from the use of two eccentrics to govern the motion of one main valve. He visualized the possibilities, from the standpoint of economy, of further utilizing the expansive power of steam in the cylinders an accomplishment hitherto had been impossible with the hook motion. So with the incentive of attaining a greater operational economy as an objective, he invented the form of valve gear that bears his name.

It was in 1848 that Walschaert first applied his new valve gear to a locomotive on a trial basis, and the results turned out exceedingly favorable just as he had anticipated. His greatly improved valve gear attracted attention throughout the Continent, and in due time it came into general use on all the principal railways of Europe. The mechanism of the Walschaert valve gear is entirely different than the general run of valve gears in that the resultant motion of the valve is due to two independent component motions; one motion is produced by the eccentric-crank-arm which moves the valve to a position of no lap plus no lead, while the remainder of the valve movement, lap plus lead, is actuated by the crosshead.

The principal distinction between the Walschaert and the Stephenson valve gears, so far as steam distribution is concerned, is that the Walschaert gear gives constant lead at all cut-offs, whereas the Stephenson gear varies considerably in this feature. The only time the valve of a Stephenson gear is operated by a single eccentric is when it is in full gear forward or full gear backwards. At all intermediate gear positions, the motion actuating the valve is not that of a single eccentric, but a combination motion produced by the main eccentric in gear and a sizeable increment of motion produced by the other eccentric. Due to the requirements of lap and lead, the angle of advance, for both forward and backward gears, the leverage effect of the two eccentrics of link motion are not in a diametrically opposite phase. If they were, the link would rock about a stationary point between the two eccentric-rod connections. Since this is not the case, any 'hook-up' in either forward or backward gear, produces a change in lead. If the arrangement of the eccentric rods is of the 'open-rods' variety, 'hookups' in either forward or backward gear, will cause an increase in lead; 'Crossed-rods' will produce a decrease in lead in the various 'hook-up' positions. 'Slip' which occurs between the slide-block and the link, is another annoying feature associated with the Stephenson gear a feature that tends to increase due to wear. However, when in perfect repair with the link in such a position that the saddle pin is directly over the slide-block, the slip is comparatively small.

In the Walschaert valve gear, the eccentric-crank-arm, attached to the main crank, is set at 90 degrees out of phase with the main crank. The eccentric rod connects with the lower end of a rocking link that is pivoted at its exact center. Connected to the link's slide-block is a 'radius rod' with one end, at the link, extended a short space to the shifting lever, which, with the customary linkages, terminates at the reverse lever. The effective radius rod extends from the slide-block to a vertical lap-and-lead lever. The lower end of this lever, through linkage, is attached to and controlled by the motion of the crosshead. Since the motion, due to the displacement of the crosshead, is greater than the motion produced by the eccentric-crank-arm, the valve stem is attached at the top, or near the top, of the lap-and-lead lever. Its exact place of attaching depends on the type of slide-valve used. The result, of the mechanical set-up of the Walschaert valve gear, is that the lead remains the same at all points of cut-off which is a desirable economic factor in the matter of efficient distribution of steam. The special adaptability and all-around efficiency of the Walschaert valve gear made its adoption and use an exclusive necessity and an absolute requirement throughout the entire era of big steam locomotives!

To complete the discussion of radial locomotive valve gears, the Baker valve gear possesses sufficient commendable qualities to justify consideration. Mr. A. D. Baker, a manufacturer of threshing machinery, was granted a patent in 1903 on a valve gear for use on traction engines. This traction engine valve gear had recognizable and unique valve-motion features that were adaptable, with considerable alterations, for being converted into an effective locomotive valve gear.

In 1911 a major patent was granted to a newly formed concern known as The Pilliod Company, which was founded to manufacture 'The Baker Long Lap Locomotive Valve Gear'. In the alterations, making the previous traction engine valve gear into a suitable and efficient locomotive valve gear, the most visable operating parts of the Walschaert valve gear were copied, such as outside installation, an eccentric-crank-arm attached to and set 90 degrees out of phase with the main crank which alone furnished a valve motion with zero angle of advance. This motion alone would call for an elementary valve without lap and would admit steam for full stroke. Motion from the crosshead, through proper linkage, like as in the Walschaert gear, gives the additional travel to the valve to make up for lap and lead. While the outside visable feature of the Baker gear are direct copies of comparable Walschaert features, some of the other parts of the Baker gear are suggestive of applications contained in the Marshall gear, a marine-engine gear.

The Baker gear, notwithstanding some of its visual Walschaert features, it, nevertheless, possessed some individually desirable qualities. It averted the use of the curved link and avoided any sliding-friction members in its mechanism. A major claim for this gear was that it provided an extra long valve travel which permitted the use of a longer steam lap.

Since the appearance of the Baker gear was pretty much of the 'Johnny-come-lately' variety, in the time schedule of the remaining few years of the steam-locomotive era, its application was somewhat local and during these remaining few years of service, it made no perceptible dent in the long and efficient record of the Walschaert valve gear!

A contributor, in a recent issue of the ALBUM, vehemently claims the Walschaert valve gear is not a 'radial type of valve gear.' However, not wishing to pursue the argument into tedium, I'll quote Prof. Furman's definition of a radial valve gear as it appears in his textbook on 'Valves and Valve Gears' which is as follows: 'The characteristic feature of a radial valve gear is that the resultant motion of the valve is taken from a vibrating link or rod. In case of the Joy gear, there is not even one eccentric, but nevertheless a vibrating motion of a link or rod is obtained.' End of quote. Therefore, the Walschaert valve gear, according to this authority, fulfills all requirements to be classed as 'a radial type of valve gear' in spite of any senseless counter claims.

Some further reverberations spewing from the same source, claims the Walschaert valve gear is a 'sloppy gear' and also a 'mechanical monstrosity!' Such inane vaporings can originate only in one suffering from a thick mental fog, and acting in a puerile and silly manner comparable to Cervantes' zany character, Don Quixote who 'jousted windmills.'

In big locomotive construction, can anyone imagine a big Articulated-Mallet locomotive, with wheel arrangement of 2-10-10-2 and rated 6,000 hp being equipped with any valve gear other than a Walschaert valve gear? In big locomotive construction, the Walschaert valve gear functioned as the heart and soul of the engines that propelled the locomotives. To consider any other equipment functioning in such an essential capacity would be just as futile and impossible as a hare-brained attempt to obtain productive results by the loony and impossible operation of 'THRESHING CHAFF!'