. The railroad and engineering journal . be seen from the motiondiagram, the ports are not only opened wide, but the valvethrows over them, or travels beyond their inner edges. QUESTIO-V 344. Howis the point of cut-off affected by the link? Answer. Changing the travel of a valve with a link has avery similar effect to that produced by eccentrics of differentthrow—that is, the period of admission is increased with thethrow of the eccentric and that for expansion lessened. Thisis shown clearly in both the motion diagram and the the first curve and a travel of i\ in. the steam is cut o
. The railroad and engineering journal . be seen from the motiondiagram, the ports are not only opened wide, but the valvethrows over them, or travels beyond their inner edges. QUESTIO-V 344. Howis the point of cut-off affected by the link? Answer. Changing the travel of a valve with a link has avery similar effect to that produced by eccentrics of differentthrow—that is, the period of admission is increased with thethrow of the eccentric and that for expansion lessened. Thisis shown clearly in both the motion diagram and the the first curve and a travel of i\ in. the steam is cut ofifat S in. for the backward stroke and 6J in. for the front, andwith 5 in. travel steam is admitted during 2o| in. of the back-ward and 20| in. of the forward stroke. Question 345. How is the point of release or exhaust of thesteam affected by the link ? Answer. As the travel increases, it is delayed until later inthe stroke. Thus, with 2i in. travel the steam is exhausted orreleased from the cylinder during the backward stroke when. Fig. 230 the piston has moved 17 in., and on the return stroke at lOJ in.,whereas, with 5 in. travel of the valve, the release is delayeduntil 23! in. of the stroke. An examination of the diagram andtable will show very clearly the relation of the point of releaseto the travel. Question 346. I/ow is tlu lead affected by the ordinary link-motion ? Answer. It is increased as the travel is diminished, as is Vol. LXIt, No. S.] ENGINEERING JOURNAL. 369 shown in the table, and also by the inclination of the curves atthe top and bottom of the diagram. Question 347. What is the cause of this change of the amountof lead ? Answer. This can be best explained by reference to fig. 229,which represents a link with very short eccentric rods. If thecenter from which the link was drawn was in the center of theaxle S, and the eccentric straps embraced the axle instead ofthe eccentrics, their ends tn and h, from .^ as a center, wouldeach describe the same arc, a b
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