The slide-valve and its functions, with special reference to modern practice in the United States; with ninety diagrams and illustrations by Begtrup Julius

Author:Begtrup, Julius
Language: eng
Format: epub, pdf
Tags: Slide-valves, Steam-engines -- Valve gears
Publisher: New York, Van Nostrand
Published: 1902-03-25T05:00:00+00:00

two points represents the entire range of adjustment of the cutoff valve in the present case. If earlier cut-off is required, the valve-space must be made smaller. For cut-off at one-eighth of the stroke, the cut-off edges would coincide, and for still shorter cut-off, the valve would overlap the port in its midled position. The motion is quickest at the middle of the throw, and the quickest cut-off is that which occurs at or near mid-throw, of the equivalent eccentric. The radius of the eccentric-circle may represent maximum speed of relative motion at mid-throw, and at other points it is represented by vertical ordinates to the horizontal diameter. It will be seen that sharper cut-off could be had for the entire range by moving point D farther back on the circle ; but this would also throw point E farther back, and would increase the diameter of the cut-off eccentric; and as it so happens that a sharp cut-off earlier in the stroke is of more consequence than later in the stroke, the arrangement here shown is generally adopted. Thus it appears that the design of the Meyer valve-gear is restricted by a desire to keep down the size of the cut-off eccentric ; and it will also be readily seen that the eccentrics cannot very well be of same diameter, unless the range of cut-off be limited to five-eighths of the stroke. The latest cut-off may occur before the main port is closed, and in that case the short period during which the cutoff valve is closed, as shown on the diagram, must be taken into account; for otherwise it may happen that the cut-off, port is open again before the main port is closed. The location of the cut-off eccentric, when the main port is closed, is found by marking off the corresponding crank-angle from point E forward. It will probably be admitted that the graphical method here shown is simpler than that invented by Dr. Zeuner; but the greater advantage of the method here presented lies in the fact that the geometrical construction is less artificial, and may readily be reasoned out, and may therefore be retained in the mind more readily than any process that must be learned

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