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Company built quite a number of engines like the one in Fig. 9, and one-an exact duplicate of the one we present—was bought by the line on which I received my first railroad experience; her performance is a legend among the older employees of that road to-day; the work that engine was capable of doing as compared with other engines with the same-sized cylinders was almost unbelievable, and was never equalled before, nor since. Finally her boiler exploded near the roundhouse at the main terminal, and she was never rebuilt.
The engine was of the double-truck class, with boiler, cab, and tender on one common main frame, while the cylinders were carried on the separate drivingwheel frame that was free to rotate on its centre bearing that supported the forward end of the main frame, and it was through this centre bearing that the steam pipe passed, the exhaust pipe being made flexible. The entire weight of the engine was on the driving wheels, and the adhesion of those small wheels to the rails was unusually great and aided the power that was developed; but it is in the cylinders that the power of the engine originates, and they were not large-16 inches by 24 inches—and I believe that the correct distribution of steam by a properly designed and worthy style of valve gear had much to do with the production of power; the results were obtained, all right.
It will be noticed that the reversing shaft in this Mason engine lies over the top of the boiler, and the bar connecting the lifting arm with the radius rod is abnormally long, whereby, as the ends of the link are swung forth and back, the link-block is carried in a line very near to horizontal.
In Fig. 10 is illustrated the revised design of the Walschaert gear that was presented and described at
media Fig. 10.—Mason's Improved Design of Walschaert's Valve
length before the Master Mechanics' Convention in 1885. Although a D-slide valve is used, the position of the valve chest is further in toward the centre line of the engine than is common, this inlying being more common to valves of the piston type. In order to deliver the motion of the combination lever to the valvestem, the upper end of the combination lever is connected to the outside of the block Q which is bolted
to the sliding guide-bar RS and a pin extends inside from block Q far enough to engage with the end of valve-stem T; this detail, however, is of the lesser importance.
The greater import attaches to the mode of suspension of the radius rod NP: While the suspension bar of the engine in Fig. 9 is longer than is found on any other engines using the Walschaert gear, Mr. Mason went to the opposite extreme in this, his later design, and in Figure 10 the suspension bar UV is not more than one-half of the length of the link itself. It was found that the point of suspension had a great influence on the motion delivered to the valve, and this point regularly varied in most types of the gear from the effect of the different angles assumed by the reversing arm that raises and lowers the suspension bar, and also, in the case of double-truck engines like the one represented in Fig. 9, by the rotation of the driving-wheel frame while rounding a curve in the track. In the plan of Fig. 10, however, there is a stationary, curved link, or guide W taking its radius of curvature, like the main reversing link, from the pin P and also containing a sliding block which is attached to, and worked by, the connecting bar from the reversing arm. The upper end of the short suspension bar is connected at U with this sliding block, and at V its lower end is attached to the radius rod; the pin U becomes the suspension point, and its arc of movement is equidistant from the arc of the main link-block, as the engine stands in Fig. 10, during all points of cut-off. The effect of this arrangement was expected to be the nearly uniform distribution of steam to and from the cylinder. It causes a remarkable slip of the link-block at each end of its stroke in working gear, either going ahead or backward, that was expected to equalize the alternate port openings, and it certainly does delay the motion of the valve at the end of its travel, holding the admission and exhaust ports more nearly fully opened at the time that they should be so.
In American locomotive design outside admission valves are generally of the plane seat, D-slide type, while for inside admission piston valves are, of course, the only kind used, yet the piston valve may be, and in a few cases is, specified for outside steam admission; but, in the latter case, the balancing of the steam pressures against the valve pistons being less perfect on account of the lessened area exposed to the live steam pressure on the back valve piston, due to the entrance of the valve-stem at that end of the steam chest.
Up to this time we have considered the Walschaert gear in connection with outside admission slide valves, while as a matter of fact, at this date the majority of