. Locomotive text for engineers and firemen; a complete treatise on the engine, electric head-light and standard code of train rules . , or piston valve, which, ifcorrect in point of length, will place the valve in thecenter of the valve-seat, when the piston is at the endof the stroke. With the lap and lead necessary for theeconomical use of steam, it is simply a question of howfar the valve should be moved to reach the desired moving of the valve to this point is the distinguishingfeature of the Walschaerts valve gear. The valve rod isengaged by an intervening union bar, which is a
. Locomotive text for engineers and firemen; a complete treatise on the engine, electric head-light and standard code of train rules . , or piston valve, which, ifcorrect in point of length, will place the valve in thecenter of the valve-seat, when the piston is at the endof the stroke. With the lap and lead necessary for theeconomical use of steam, it is simply a question of howfar the valve should be moved to reach the desired moving of the valve to this point is the distinguishingfeature of the Walschaerts valve gear. The valve rod isengaged by an intervening union bar, which is attachedto the crosshead, and the corelation of the short distancebetween the union bar and the bar driven by the eccentricrod and radial link, and the lower end of the union bar,becomes the determining factor in moving the valve awayfrom the central position to the point desired. The action of the intervening union bar is such that atthe opening of the valve the motion is accelerated, and arapid opening at the end of the stroke of the piston be-comes a peculiarity of the valves motion, in addition to WALSCHIAERTS VALVE GEAR. 281. 282 WALSCHAERTS VALVE GEAR. which the opening becomes a fixed quantity, unchangedby the variations of valve travel. Adding to this the factthat the intervening radial link oscillates in a much small-er arc than is the case with the Stephenson valve gear, itcan readily be seen that the regularity of the movement isat all times under perfect control, and the path of the arccan be defined with a degree of exactness that leaves littleor nothing to be desired. Indirectly, other benefits followed the introduction ofthe Walschaerts valve gear. The absence of the linkmotion permits easier access to the driving boxes from theinside, and for the same reason it has been practicable tointroduce strong bracing between the frames in orderto lessen frame breakage, which has been one of the great-est sources of expense in locomotive maintenance. Adjusting the Valve Ge
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