In the subjoined engraving, Fig. 1 represents an end view of the two engines, and FIg. 2, a side view of one of them. The letters refer to the same parts in each. The cylinders a a are of cast iron, and fixed to a framing, which is bolted to the bottom of the boat. . The piston-rods b b, are keyed at the upper ends, to the cross heads e c; to the exterior ends of which are attached the connecting-rods d d. The lower ends of these connecting-rods are inserted in the fork end of the beams e e, which vibrate upon a shaftf, the bearances of which rest upon the top of the condenser g. In the same forks are inserted the ends of other connecting-rods k is, which are keyed at their upper ends to cross heads i i. In the centre of these crossheads are bushes large enough to receive the rods j j, which extend to the crank pins of the cranks k k. These cranks are fixed to the main shaft, which rests upon the bearances the arches ni, which are bolted to the cross beam, as at a. The shafts are shown as broken off at the outer ends, but they extend to the outside of the peddle wheel.
The side beams e t, are not straight, but have two bands, represented by the lighter parts of the stading, the ends near the cylinder being therefore much farther apart than the opposite ends, so that they may take up as little room as possible, by lying close to the respective parts of the machinery. They are also forked at the end nearest the air-pump o, so as to admit the insertion of the pump-rods p, which are connected at their upper ends to the cross-head, in a bush, iu the centre of which is keyed the air-pump rod r. Connec • s, are attached at t, to the aide beams e, and at their upper ends to cross- eads, which are connected as at a a, (Fig. 1,) to two rods, which work the plungers of two feed-pumps v, for supplying the boiler. j is the apparatus for blow ing through, previous to starting the engine. It consists of a cock, which opens or closes a communication between the steam-chest and condensers, by turning the handle. The rod and lever x, are for the purpose of regulating the quantity of injection water which enters into the condenser, by a pipe from the outside of the vessel, and can be increased and lessened in quantity, by turning a cock to which the rod a is attached. y is the hot-well, into which the condensing water is discharged from the air-pump. The feed-pumps are supplied with water from this hot-well, through the medium of a pipe, the overplus being dis charged through the side of the vessel, by another pipe which is not seen. In the steam cbest 1, is contained the sliding-valve. For the purpose of explain ing its principle, we shall here introduce a separate diagram, which may be taken as a representation of the best form in which it is constructed, though it varies somewhat in its relative position from that of the engine we now describe. The
cylinder a, in the following figure, has two apertures b e, at top and bottom, to which are bolted and cemented the upright pipe d, having near its centre, or in any other convenient part, a broad face represented at in which are three ob long holes, the upper one running into the cylinder through b, and the lower one into the cylinder through c. The middle one communicates with a sepa rate recess h, to which is attached a pipe, which forms a communication with the condenser. The steam chest', is a rectangular box of cut iron, and has a pipe attached to it from the boiler; this chest is covered over and made steam tight by a lid g screwed Wit. On the upper side of the steam chest is a stuffing box, through which passes a turned rod for working the slide-valve A, which is represented in section.
This valve has a flat face, neatly ground to the surface e, sufficient to cover two of the holes of e, and twice the breadth of any one of the surfaces interven ing between any of the holes in e. The valve is raised into a box from its open interior part, being of sufficient dimensions to cover, in its present situation, two of the passages e, and leave open a third, the bottom one in the present instance being open.
If steam were admitted into the steam chest whilst the valve was in its highest position, it could only enter into the cylinder through c, and consequently would cause the piston to ascend, whilst the air above it would be discharged through 6, and the open part of the valve, and so into the condenser. But suppose the valve to be depressed so as to cover the middle and lowest holes, then the steam from the boiler would have free communication with the upper side of the pis ton through b, which it would consequently force downwards, whilst the steam used in the ascending stroke would be discharged into the condenser, through the interior of the sliding valve ; so that by changing the situation of the valve, the piston may be made to ascend or descend at pleasure. The mode by which the valves in the engine before mentioned are worked, is by eccentrics on the main shaft, which work cranks ; a spindle extends across between the support ing columns, in the centre of which is another crank, which gives motion to a slide-rod, through the medium of two other rods. The piston-rods and cross heads reserve their vertical motion by horizontal bars, having adjustable brasses on their outer ends, fitted to the columns, upon which they work smoothly up and down. The framing of the two engines is bound together by eight bars, meeting together in the ball 10, upon the top of which is fixed a lamp 11.