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 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 



