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more and Ohio Railroad by the American Locomotive Company, in which the rear, or high-pressure, engine has a piston valve which we may know, by reason of the foregoing explanation, is of inside admission. The forward, or low-pressure, engine has a plane seat, D-slide valve, and is necessarily of outside admission, but anyhow, we should know this on account
Fig. 13.--Diagram of Valve Gear, Low-Pressure Gear, or
Forward Section of Mallet Compound Locomotive.
of the location of the eccentric and the connections at the upper end of the combination lever; and in Fig. 13 is shown an outline diagram of the latterthe low-pressure section of the engine—with the positions of the combination lever and link, and the lifting arm, at the different phases of a cycle of motion or revolution of the driving wheel.
As an illustration of the different ideas held by prominent American locomotive designers, compare Figs. 10 and 11: It concerns their opposite views
in regard to the supposedly important point of radius rod suspension. The Mason theory in connection with the guide for the point of suspension is that the suspension bar must be so extremely short as to admit of a pronounced swing to the radius rod. The American Locomotive Company's very recent production shown in Fig. 11, has no swing suspension whatever. The lifting arm of the reversing shaft has a block pivoted at its end which acts as a guide for the extended end of the radius rod, so that with the reverse lever in either gear, forward or back, the motion of the link as the engine works cannot cause any vertical shift of the link-block, and the only variation of the block from a true horizontal motion will be the slight amount due to the angularity in the position of the radius rod and the effect of the oscillation of the short (upper) end of the combination lever.
The engine built for the Chicago, Rock Island & Pacific Railroad, that is represented by Fig. 14, was built by the Baldwin Locomotive Works, and has the Walschaert motion and external admission, D-slide valves, but there is a variation here from the general manner of making the connection from eccentric to link: the eccentric rod is not connected directly to the “foot” of the link, but the trunnion, or fulcrumpin, of the link has become a shaft, working in bearings in a “box,” and to the outer end of this shaft is
attached an arm extending downward and to the lower end of which the eccentric rod is connected, the radius rod and other parts of the gear remaining as usual. Such variations are sometimes found necessary for convenience in applying the gear to engines of peculiar construction, and one of the chief recommendations for the Walschaert motion is that it may be applied to any oddly designed engine with a minimum of change from the simplest model, and there is no conflict to expect with other parts of the machinery: An illustration of this, and the general adaptability of the Walschaert valve gear, is Fig. 15, a motorcar built for the Erie Railroad.
The locomotive exhibit at the Louisiana Purchase Exposition, at St. Louis in 1904, included the heaviest engine in the world, as represented by the Mallet Compound already referred to, and another one, typical of a class that has become renowned all over the world for swiftness—the French De Glehn Compound: Two engines, built for the extremely opposite in railway service to be the fastest and to be the strongest; and that the valves of both are actuated by Walschaert's style of gear is proof that it was a mistaken theory, which was held by some, that it is only on certain types of engines, or those engaged in a certain class of work, that the Walschaert valve gear is in any way superior to the Stephenson link motion.