. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . gine, the valve opens the portfor the admission of steam before thepiston has finished its stroke from theother direction. The amount which thevalve has opened the port when the pis-ton has reached the end of its stroke,is called the linear lead and is usuallyindicated by V e. The angle correspondingto this lead is called the lead angle andis called y (gamma). The linear lead may be from .10 to .15in. using, in large engines, up to .25 the corresponding lead angle runsfrom 2° to 4°.
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . gine, the valve opens the portfor the admission of steam before thepiston has finished its stroke from theother direction. The amount which thevalve has opened the port when the pis-ton has reached the end of its stroke,is called the linear lead and is usuallyindicated by V e. The angle correspondingto this lead is called the lead angle andis called y (gamma). The linear lead may be from .10 to .15in. using, in large engines, up to .25 the corresponding lead angle runsfrom 2° to 4°. At any rate it is essentialthat the linear lead should not be madetoo great, else there will result a uselessconsumption of steam. 90 RAILWAY AND LOCOMOTIVE ENGINEERING April, 1922 When the maxinlum angle of admissionhas been determined together with the de-sired port opening and the Hnear lead orangle of lead, it then becomes possible,by graphical means, to ascertain the nec-essary outside lap, as well as the throw ofthe eccentric for driving the valve as wellas the angular advance of the The lead angle increased by 90° will givethe angle at which the eccentric shouldbe keyed to the crank. In most cases it is the linear lead andnot the lead angle that is assumed. Inthis matter, for the first example that is:given. there will be assumed a given angle■of admission t, (epsilon) the maximumport opening a K and the desired linearlead \o from which there is to be deter-mined the outside lap c; the eccentricity orhalf throw of the eccentric Q the leadangle 7 and the angular advance of theeccentric 5 (delta).
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