EXPLANATION OF THE PLATES. 
337 
PLATE IX. 
The apparatus for opening and closing the steam passages is of more importance 
to the perfection of the steam engine, than any other part of its mechanism. In the 
present state of the engine the action is either very complicated or imperfect: my 
object in this plate is to show how the imperfection of the most simple method may 
be avoided, and also how it may be applied to reciprocating movements. 
Fig. 1. shows a section, 1 2 and Fig. 2. a plan, of an apparatus for opening and 
closing the steam passages by means of the rotary motion of the crank shaft D : 
the object of the method is to give such a form to a wheel on the shaft D as will 
move the pin e twice during the stroke, and in the easiest and quickest manner. 
For this purpose the shaft passes through a rectangular frame which rests in grooves 
on the shaft to keep it in its place, with liberty to slide backwards and forwards; 
and it is provided with two rollers, to be acted on by the curved surfaces of a wheel 
fixed on the shaft. The curve H G moves the valves at the termination of the 
stroke, and I K shuts off the steam, that the engine may work expansively the 
rest of the stroke. In order that there may be the power of varying the time of 
cutting off the stroke, the curve I K may be on a separate piece M, (Fig. 2.) capable 
of being moved from N to 0. The apparatus is supposed to move a slide of the 
kind represented in Plate v. Fig. 1; but is equally applicable to move the four- 
passaged cock, (art. 456 and 458) or valves. For the nature of the curves, see 
art. 481. 
Fig. 4. and 5. represent the same principle applied to a reciprocating motion. 
The plug-tree A B is kept in its place by guides on the brackets; these guides 
slide in the dark grooves. The curved parts H I, C D, K L, &c. successively 
move, horizontally, the frame C on four rollers supported by the brackets attached 
to the engine; and by the backward and forward motion it turns the axis E, and 
raises or depresses the lever F, which acts on the rod of the slide. The same move 
ment would obviously open valves or turn a cock. By the lever on the right-hand 
side, the roller frame may be moved by hand ; but by not reversing Fig. 5. it has 
been shown there on the left. See art. 483. 
Fig. 3. represents the method of opening valves by weights, the plug-tree A B 
being made a means of raising the weights, and of disengaging them by the 
tappets/, d. See art. 478. 
1 Fig. 1., as represented in the Plate, is too much limited to allow the motion to be reversed. 
2 U