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would be economised. This has been attempted, and in some instances with considerable success, by the introduction of the direct-action engine. The varieties of this class are very numerous. To the reader anxious to have a knowledge of these, we must refer to larger works; the Artisan treatise gives many illustrations under this head. Our space permits us only to give some simple diagrams illustrative of the most noted of these. The distinguishing feature in this form of engine is the absence of the side beams, rotatory motion being given at once to the paddle-shaft from the piston-rod. In fig. 166 we give a diagram illustrative of the
“steeple-engine," much used in the Clyde. a is the piston-rod, carrying a triangular cross-head bb; c the paddle-shaft
, d the connecting-rod, attached at one end to the upper extremity of the cross-head bb; and the parallelism of the piston-rod is maintained by the guide e, in which the cross-head m works.
In fig. 167 we illustrate the arrangement of the Siamese or double
cylinder engine introduced by Maudsley and Son. ab the two cylinders, ee the piston-rods connected with the cross-head ee, which is continued downwards to d, and which slides between the two parallel guides e; one end of the connecting-rod is attached to e, and the other to the crank g, on pedestal f. In fig. 168 we give a diagram illustrative of another form of direct-acting engine, which is considered as exceedingly compact; “indeed,” says an authority, “no engine can occupy less room than this ; for its length is little more than the diameter of the cylinder.” Let a represent the piston-rod, b the connecting-rod, cc the paddle-shaft, d the air-pump rod worked by an eccentric on the shaft cc. The cylinder-valve is worked by the eccentric-rod f, fig. 169, from an eccentric on shaft cc fig. 168; the rod f works the levers a and valve-rod g; h the pedestal fixed to the pillar e; m is the eccentric-rod working the air-pump rod n corresponding to d, fig. 168. In direct-action engines, where the connecting-rod is between the piston and the crank, the engine is designated as belonging to the class known as the “Gorgon engine,” introduced by Messrs. Seaward, where the connecting-rod is above the crank a; they come under the designation of steeple-engines.
A well known form of direct-action engine is that known as the “oscillating.” We have already described the action of this; we now give a diagram showing its application to a paddle-wheel steamer (fig. 170).
Where vessels are propelled by the “screw," engines differing in arrangement from those we have already described are adopted. The screw having to make so many more revolutions than paddles in the same space of time, the speed of the screw-shaft is sometimes brought up by cogwheels. In the engines of the Great Britain this arrangement is adopted; a pair of oscillating engines giving motion to a horizontal shaft; in this is fixed the driving wheel, taking into the toothed wheel on the screw-shaft. The inconveniences attendant on this form have, however, prompted in
other instances the use of engines connected directly to the screw-shaft; the difficulty in this case, however, is, that the valves of the air-pump are liable to be knocked speedily to pieces from the high speed at which the engine works. Mr. Bourne proposes to obviate this by replacing the air-pump valves by a species of ordinary slide-valve.
In fig. 171 we give a drawing of a double-geared engine, adapted for screw propulsion by Messrs. Scott and Co. of Greenock. The drawing shows a transverse section of the ship, showing the engines in complete external front elevation. The cylinders are fifty-two inches diameter, and three feet nine inches stroke, placed diagonally athwart the ship, and at right angles to each other; whilst the piston-rods project through the lower covers, to allow of long return connecting-rods. Each cylinder has two piston-rods, for greater steadiness, their outer ends in each case being keyed into a cross-head fitted at each end with slide-blocks, for working in a pair of inclined open guide-frames bolted to the bottom cylinder-cover, and supported beneath by projecting bracket-pieces, recessed and bolted down upon pedestal pieces on the engine sole-plate. From each end of this cross-head, immediately outside the guide-frame, a plain straight connecting-rod of round section passes up, to actuate the main first-motion shaft. The upper ends of these connecting-rods are jointed to side-studs, or crankpins, fast in two opposite arms of a pair of large spur-wheels, which give motion to the screw-shaft by means of a pair of corresponding spurpinions, fast on the shaft beneath a single pin in each wheel, answering for the two opposite connecting-rods on the same side of the engine. The main spur-wheels are eleven feet five and a half inches diameter, with one hundred and eight teeth of four-inch pitch, and fourteen inches in breadth on the face. They are keyed on the extremities of a common shaft, which is conveniently placed in the angular space formed by the two ends of the inverted steam-cylinders, being carried in a pair of pedestals cast with angular bracket-pieces to bolt down upon the cylinders.
The wheels are equally compactly placed, one on each side the cylinders and the general mass of machinery, and just filling up the space inside the connecting-rods. The pinions on the screw-shaft are four feet six inches diameter, so that the ratio between the screw and the engine’s rate is two and a half to one. By this arrangement each piston is directly coupled to both of the large wheels, and the increased length of the crossheads which the plan involves is counterbalanced by the effect of the double piston-rods; for by this division of the pressure the cross-strain leverage is proportionately diminished. The system of duplex gearing also insures a good, substantial, and well-balanced connection of the first-motion shaft with the screw-shaft. The air-pumps are both situated on one side of the engines, and are worked from the connecting-rod stud of the spur-wheel on that side, the pump cylinders being bolted at their lower ends by their foot-branches to the sole-plate, whilst their upper ends are connected together by a couple of arched cross-pieces. They are thus well bolted together, and to the main framing, their intermediate connecting brackets answering to carry their stud centres of a pair of bent levers for working the bilge and feed-pumps. The whole of the pumps are constructed on the trunk principle, of which class Mr. Humphries' engines, of the Dartford, are so well known as the earliest type. As the throw of the main driving-studs would be too great for the purposes of the air-pumps, it is very ingeniously reduced by means of an eccentric set upon the stud, so as to bring the real working centre nearer to the centre line of the first motion-shaft. One of the connecting-rods for working the pump is formed in one piece,
with the eccentric ring, and the other is jointed to the ring on the opposite side; both rods descending to joint eyes on the upper ends of links which are again connected by bottom joints, in the recesses of the plunger-trunks of the pumps. The same intermediate joints of the lower ends of the connecting-rods also afford the means of connection with the upper ends of the bent levers of the bilge and feed-pumps, which levers serve the purpose of radius-bars for the air-pump rods. The links for working the plungertrunks of the bilge and feed-pumps are jointed nearly at the middle of the bent levers, so as to give the required short stroke, the pumps
themselves being set vertically, one on each side the screw-shaft, on the sole-plate. The cylinder-valves are combinations of the four-ported class, so successfully introduced on the Clyde by Mr. Thomas Wingate, and the equilibriumvalve. With this arrangement, the engines are handled with very great facility, and a very free exhaust is obtained. They are actuated by a pair of eccentrics on the main first-motion shaft, rods from which pass upwards to short levers on a pair of parallel rocking-shafts, working in end-bearings overhead. These bearings are carried upon a pair of parallel arched framepieces, stretching across between the two valve-chests, so that they thus bind the upper ends of the cylinders. The rocking-shafts are cranked at their centres, and have short connecting-rods jointed on to the crank-pins, and extending right and left to their respective valve-spindles. The steam enters the valve-chests on each side, through the elbow-branches, opening into stop or expansion valve-chests at the lower corners of the valve-casings, and the exhaust steam passes off to the condenser by passages round both sides of the cylinders. The condenser is entirely within the engine, beneath the cylinders; it answers, indeed, as the supporting pedestal for the cylinders, which are bolted down
it. Of engines adapted to drive the screw-propeller direct, without the intervention of gearing, recently introduced, the "trunk-engine,” by Messrs. Penn, of Greenwich, is most remarkable; it is coming fast into general
In this form of engine, the direct connection between the piston and crank obtainable by the oscillating engine is obtained without the inconveniences arising from the vibration of the cylinder. To the piston a hollow trunk or tube is attached; this passes through the cylinder-cover; between them a packing is interposed, to prevent any leakage between the trunk and the cover; the trunk is of such length as to project beyond the cylinder-cover when the piston is at the bottom of the cylinder. The trunk is of considerable dimensions; the connecting-rod is connected by a moveable joint to the piston, and its other end to the crank-pin; as the piston moves backwards and forwards, the connecting-rod vibrates within the trunk, and thus the direct action is obtained by very simple means.
The trunk is on both sides of the piston, or, in other words, the piston is placed midway in the trunk, the connecting-rod being connected with that side of the piston nearest the crank. In this class of engines the cylinders are horizontal and placed side by side; the air-pumps are also horizontal; the great aim being to have all the machinery as low as possible beneath the water-line, a most important point in vessels of war. Both ends of the trunk pass through stuffing-boxes in the cylinder-cover; by this arrangement the pressure of the steam-side is prevented from preponderating over the other. In fig. 172 we give a diagram illustrative of the arrangement of the trunk-engine. Let a a be the piston, bb the trunk on the crank side,