Page:Valve-gears for steam-engines (IA valvegearsforste00peab).pdf/96

 VALVE-GEARS FOR STEAM-ENGINES.

84

but at other grades of the Hnk the lead was sensibly equal. Had the link been set to give equal lead at full-gear, then the mid-gear lead would have had an inequality of yL of an inch in half an inch, which would not have any appreciable effect in the running of the engine.

TABLE III.

Rocker used—link-pins 2 7/8 inches back of link-arc. Cut-oflf equalized at 1/2 stroke and at full-gear. Saddle-pin 5/32 of an inch back of link-arc. Distance between link-pins 14 inches.

Cut-off.

Port

Lead.

a H.E.

6 9

b

C.E.

5li

8ff

Slip.

Travel.

Diff.

a

Opening.

Sl b.

M

9

3¥

T^^

t

2i

i

if

if

2|

f

i

3t6

29 33

li

3

3^

12

12

15

14M

33

f

18

^m

A

5

1^

21

io

tV

T%

22^

22M

3%

1

-7I3

tV

233

tV

3t

ItV

I

4il

If

li

6i

2^

H.E. C.E.-jV

In the third example the cut-off was equalized at |- stroke and at full-gear as recommended by Auchincloss in his Link and Valve Motions^ by the method described on page 77 and shown on PI. XXI. With the ratio of crank to connecting-rod used in these examples, i.e. 1:5, the reverse-shaft was found to interfere with the eccentric-rods at full-gear backing. The table shows that the equalization of the cut-off was nearly perfect from half-gear to full-gear. The inequality in the cut-off increases as the cut-off is shortened, that is, at the place where it has the most deleterious effect; but it must be admitted that