Valve gears by Fessenden Charles Horace

Author:Fessenden, Charles Horace
Language: eng
Format: epub
Tags: Steam-engines
Publisher: New York [etc.] McGraw-Hill book company, inc.
Published: 1915-03-25T05:00:00+00:00

The length of the port is usually about 3/4 the cylinder diameter;

3/4X8 = 6" = length of port.

2 14 Therefore w = -^ = 0.357" o

The various steps in the construction of the diagram to determine the laps, valve travel, and angle of advance, are explained in connection with Fig. 93.

Instead of trying to make the admissions equal at the expense of unequal cut-offs, the attempt will be made to secure a better division of work between the two ends by making the leads unequal and in that way causing the cut-offs to be more nearly equal. In endeavoring to adjust a number of undesirable things without too much sacrifice of desirable characteristics, the designer must use his judgment. He will usually find it necessary to make more than one trial before satisfactory results are obtained.

After drawing a pair of axes through 0, Fig. 93, and a circle to represent the path of the crank pin, locate m and m' at 25% of the stroke from each end. As a preliminary trial choose the leads so that the head end lead will be 1/16" and the crank end about 1/8", giving an average of 3/32" which agrees with the given data. It may be desirable to change these after partially completing the diagram. The head end lead of 1/16" should be laid off above the horizontal axis and the crank end lead 1/8" below the horizontal axis in the usual way.

A short distance to the right of the point m choose the time of head end cut-off at g and swing the arc to locate the crank position OC. Just how much to the right of m this cut-off should be taken can not be told until after it is seen how the choice works out when compared with the other events.

The computed width of maximum port opening is 0.357". If this is used on the head end the crank end opening will be unnecessarily large, yet if this value is used on the crank end the opening on the head end will not be sufficient and will cause too much throttling. As a compromise, a maximum port opening of 5/16" will first be tried on the head end.

Having determined, temporarily at least, the crank position for head end cut-off, the head end lead, and the head end maximum port opening, the diagram can be partially drawn to locate

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.