145. In order to prepare for setting the engine to work, all the three valves must be opened at once. This is done by relieving the spindles from their several catches, when the weights immediately open the valves. The steam enters through the valve F into the top of the cylinder, and by the piper through the lower steam-valve O, into the bottom of the cylinder; also through the exhausting valve K into the condenser L, driving before it some air which passes out at the snifting-valve w. At first the coldness of the parts condenses all the steam which enters; and it is not until all the iron with which the steam comes in contact is heated to the temperature of boiling water, that the steam ceases to flow from the boiler in a stream, and be condensed as it arrives at the cylinder and condenser; but after this the steam acquires the same force in the cylinder and pipes that it has in the boiler; it then occupies every cavity and crevice of the engine, and in a little while displaces all the air in the cylinder, condenser, and pipes, which passes out, and is discharged at the sniftingvalve w. This valve is always covered with water in a small cistern attached to the side of the large one to ensure its tightness. Through this valve the air is discharged by the steam, not at every stroke, as in Newcomen's engine, but only at first setting the engine to work, and this operation is called the blowing through. It is well known when the cylinder and other vessels are properly heated, and the air discharged, by a very smart crackling noise at that valve like a violent decrepitation of salt in the fire; this noise being occasioned by the water in the small cistern producing a sudden and rapid condensation of the issuing steam when the air is all gone. 146. It being known by this sign that all parts of the engine are cleared of air, all the three valves are to be shut by pressing and holding down the two upper handles x, y, and lifting up the lower handle z, in which situation its catch, 2, will retain it. This cuts off the farther supply of steam from the boiler, and also intercepts the passage of the steam from the cylinder to the condenser; and, as the cold surface of the condenser still continues to condense a considerable portion of steam, there will soon be none left, and a vacuum will be formed in the condenser, while the cylinder both above and below the piston is full of steam. The vacuum in the condenser will soon become perfect from the external cold alone, though more slowly than when an injection is made. 147. In this state the engine is prepared for starting at a moment's notice, by the engine-man letting the two upper handles, r and y, rise up, by their respective weights: this opens the upper steam-valve, and the exhausting and injectionvalves; the former admits the steam into the top of the cylinder to press upon the piston; while the latter allows the steam, already in the lower part of the cylinder, to flow into the vacuous condenser; and at the same instant that he opens the injection-cock the valve is lifted at the same time with the exhausting-valve: this admits a jet of cold water into the condenser, and condenses the steam as fast as it arrives from the cylinder, so that in an instant all the steam in the lower VOL. XXI. part of the cylinder will be drawn off and condensed. The pressure of the steam on the piston, being now unbalanced by any thing beneath the piston, it descends and draws up the pumpbuckets and columns of water in the pumps, with a velocity proportioned to the pressure of the steam and the diameter of the piston, compared with the height of the column of water in the pumps, and the diameter of the bucket: but, the piston having descended about one-third of its stroke, a chock of the plug-frame R meets the upper handle r, and, pressing it down, shuts off the steam from the boiler. That part of the handle on which the chock acts becomes perpendicular when the valve is shut, the handle being bent for that purpose; and the chock can there fore descend farther, and slide against the perpendicular part of the handle, which is straight, without producing any farther depression of the handle, at the same time that it keeps it down to the same point, so as to hold the valve shut. The piston, therefore, continues its descent by the farther expansion of the quantity of steam at first let into the cylinder; but, having arrived at the bottom of its stroke, a chock on the opposite side of the plug-beam R seizes the middle handle y, and presses it down, which pushes the rod 4, until it shuts the exhausting-valve K, and also the injection-valve by the strap and rod 9. When the catch 1, of this handle y, presses on the upper hook t, of the detent tv, it relieves the catch 2, of the lower axle z, and then the weight n causes the handles to fall, and, pulling the rod 14, opens the lower steam-valve O. Let us now consider the position of the engine; the middle handle y will be held down, by its catch 1 holding in the upper hook t of the detent so as to keep the exhausting-valve K shut; and the upper steam-valve F is also kept shut, by the same means which kept it shut during the latter two-thirds of the descent of the piston. 148. Under these circumstances the piston is at liberty to rise by the action of the counter-weight S, because the opening of the lower steam-valve O has established a free communication between the top and bottom of the cylinder, and the steam in the top of the cylinder can flow through the pipe r, and enter the bottom of the cylinder, as fast as the piston rises, by the action of the counter-weight. 149. When the piston has returned to within one-third of the top of the cylinder, the chock of the plug-frame quits the upper handle r; but this handle cannot yet be thrown up by its weight to open the upper valve, because the rod 5 from the lever of the middle axis bears up the short lever 6 of the upper axis ; and thus the motion continues till the piston arrives very nearly at the top of the cylinder: a chock on the plugframe then seizes the lower handle z, and, lifting it up, shuts the lower steam-valve; and the catch 2 of the lower axis, passing the lower hook v of the detent, moves it on its centre so as to release the catch 1 of the middle axis from the upper hook t of the detent. This being the case, the weight of the middle axis causes its handle y to fly up, and by the rod 4 it opens the exhaustingvalve; and, by drawing the strap and rod 9, it opens the injection-valve; at the same time the K upper axis, losing the support of the rod 5 which kept it up, its weight carries up the upper handler, and, by pulling the rod 2, it opens the upper steam-valve F. 150. The steam from the boiler is now admitted to press upon the upper surface of the piston, while the steam from the lower part of the cylinder beneath the piston rushes into the condenser, where, being met by the cold injection, it is condensed, and makes a vacuum in the lower part of the cylinder, which brings down the piston to make another stroke. 151. At one-third of the descent the plugframe, as before, presses and holds down the upper handle to keep the upper steam-valve shut; and, when the piston has arrived at the bottom, the plug-frame presses down the middle handle y to shut the injection and the exhaustingvalves; and in catching, this discharges the lower axis, and the weight thereof opens the lower steam-valve. The piston then rises by the counter weight, and when at the top of its stroke the plug-frame lifts the lower handle 2, and shuts the lower steam-valve; and, in catching, discharges the two other handles, which open the upper steam-valve, the exhausting-valve, and the injection-valve, and this produces the descent of the piston as before. 152. If the air has been fully discharged from all parts of the engine by blowing through, the action of the air-pump does not begin until the injection-water and the air, which are extricated from the water in the boiling, have accumulated in some quantity in the condenser; then at every descent of the bucket d of the air-pump it dips into the water contained in the bottom of the barrel N, and the water passes through the valves in the bucket: these valves shut when the bucket is drawn up, lifting all that water which is above them up to the top of the barrel, and there it is forced out through the hanging-valve g into the hot-well g. The drawing up of the bucket at the same time makes a vacuum in the pump-barrel beneath it; and if this vacuum is more perfect than that in the condenser, which it will be if the condenser contains either air or steam, it will press by its elasticity upon the surface of the water in the lower part of the condenser, and force it through the hanging-valve at m into the lower part of the barrel N of the air-pump; and, when all the water is gone from the condenser, the air or elastic vapor which is in the condenser will follow and enter into the pump until the space of the barrel beneath the bucket is filled equally with the condenser. 153. This takes place while the pump-bucket is at the top of its barrel; and on the descent of the bucket the space beneath it is diminished until it compresses this rarefied vapor so much, that its elasticity will be sufficient to close the hanging-valve m, and to lift the valves in the bucket d, and pass through them into the space of the barrel above the bucket: and, when the bucket has descended to the very lowest, the water contained in the bottom of the barrel, not being able to escape through m, must pass up through the valves, and rest upon the bucket d. When the bucket ascends it carries before it this water and air, and as it rises the space of the barrel above the bucket diminishes, and the rare vapor or air in it condenses by being crowded into less space, until at last it becomes equally dense with the atmospheric air, and then the water following it drives it through the valve g into the open air. 154. The ascent of the bucket d left a vacuum beneath it as before, and this drew a portion of the air or vapor from the condenser into it ready to be extracted by the next stroke. As soon as the bucket begins to return the discharge-valve g shuts, and prevents the atmospheric air from entering into the pump. By this we see that, if the vapor in the condenser is so rare that the whole contents of the barrel of the pump will only make a few cubic inches, when reduced to become equal to the pressure of the atmosphere, this small quantity will be effectually evacuated through the discharge-valve g, because the water resting upon the bucket follows the air, and will chase every particle of it from the top of the pump, and then follow itself. 155. An effective and economical steam engine, imparting a primary rotatory motion, has long been a grand desideratum in the arts. The importance of such an invention will be apparent, when it is considered that, although the reciprocating steam engine (whether we look to the admirable expedients for adapting it to the end proposed, or to the skill displayed in the workmanship) appears to have reached its utmost degree of perfection, yet it absorbs half the power of the steam. 156. This fact may be proved by calculating what pressure on the pistons of reciprocating condensing engines is required to produce the declared powers. The results will prove generally to be only from six pounds to six pounds and a half per square inch, on the pistons of small power engines; seven pounds as to engines of from ten to thirty horse powers; and from seven pounds and a half to eight pounds as to engines of larger powers; when the actual pressure of the steam is at least seventeen pounds per square inch above a vacuum. When the engine is in the best possible working state, these results will be a little more; but this state is seldom long maintained; therefore they may be taken as a fair average. This serious loss of power is occasioned principally by friction, and in alternating the movements of the parts. Now to obviate these defects, a variety of rotatory steam engines have been suggested. These may be examined nearly in the order of their invention, commencing with that invented by Mr. Masterman : 157. Plate XII., fig. 1, represents a vertical and central section of the troke (being that part of the engine which revolves). Fig. 2 is a trans verse section of it, and of the two masks afte mentioned. The troke is composed of the axis, of the nucleus (being the central part, and through which the axis passes); of the annulus (being a hollow ring, in which are placed valves); and of the radii (being the steam passages between the nucleus and the annulus). Fig. 3 is a plan of the nucleus. That part of it which is included between the two concentric circles is called the face. The surface of the face is a perfect plane. The axis passes through the hole 1 at right angles with the plane of the face. Six holes 2, of similar figure and dimensions with each other, are sunk in the face at equal distances, in a direction parallel to the axis, for three or four inches; then, curving into a direction at right angles with the axis, they open in the periphery of the nucleus. 158. The annulus A consists of six equal segments. At each of their joints is fixed a valve, which, by being ground on its seat, is rendered steam-tight when closed. 159. The radii 1, 2, 3, 4, 5, 6, are connected with the nucleus and annulus, so as to form steam-tight communications between each hole in the face, and the inside of the annulus. 160. Fig. 4 is a plan of the inner mask, being a circular plate of metal, of equal diameter with the face, about two inches thick, and having each side perfect planes, parallel to each other. 161. There are four holes 1, 2, 3, 4, through t: 1 is of sufficient size to admit the axis; 2, 3, 4, are each one-sixth of the space that would be included by completing the two concentric circles, segments of whicn form the sides of those holes; and those circles are described with the same radii as the segments of those which bound the holes in the face. Thus, each of those holes would extend over one of the holes in the face, and one of the adjoining spaces. The space between 2 and 3 is of such dimensions as just to cover completely one of the holes in the face; 4 is situated so as to leave equal spaces between it and 2 and 3. 162. The periphery of this mask is clasped by an iron hoop, from which projects a lever, extending nearly to the annulus, and having a small inclined bar placed across its end. The two projections from fig. 4 represent the beginning of the lever; and the whole of it, with the hoop, is represented by the dotted lines m in fig. 1. 163. Fig. 5 is a plan of the inner side of the outer mask. Fig. 6 is a plan of its outer side. This mask is a circular piece of metal of the same diameter, and about the same thickness, as the inner mask. The inner side, fig. 5, is a perfect plane; 1 is a hole sufficiently large to admit the axis; 2, 3, 4 (see fig. 6), are pipes which enter the outer side of this mask, and open in its inner side. The apertures are represented by the three smaller circles in fig. 5. 2 is the pipe through which the steam passes from the boiler to the engine. 3 is the eduction pipe, through which the steam is discharged from the engine into the condenser, or (where one is not used) into the air. 4 is a pipe through which any waste or excess of water in the annulus may be supplied or withdrawn; it is kept closed by a stop-cock while the engine is at work. The axis passes through 1 in both masks; the inner mask is placed next the face, the other next the inner mask, and both are kept closely pressed towards the face (by means of screws acting on the back of the outer.mask) so as to be steamtight with each other, and with the face; a trifling pressure suffices to make them so, the opposed surfaces having been ground on each other. The outer mask is placed in such a position, with respect to fig. 1, as that the pipes 2 and 3 may be horizontal, and point towards radius 2 (it appears in this relative position in fig. 6), and it always remains stationary. The inner mask is placed in such a position, with respect to the outer mask, as that pipes 2, 3, 4, in the latter may communicate with the holes of corresponding numbers in the former, and thus form a communication between the pipes in the outer mask and the face. It appears in this relative position in fig. 4. 164. Thus the holes in the inner mask are for the same relative purposes as the pipes in the outer mask marked with corresponding numbers. 165. The inner mask is moveable by means of m, but so far only as not to interrupt the communication between 2 and 3 in the outer mask and the face. 166. The transverse sections of both masks, placed in their relative positions, are represented in fig. 2. 167. The corresponding letters in figs. 1 and 2 refer to the corresponding parts in each figure; pp is the axis; q, q, are its bearings; r is a crank attached to the end of the axis, for working the feeding pump, and (where a condenser is used) the air-pump. As the valves, and the gear for regulating them, are precisely the same in each segment of the annulus, only two of them (one showing their position closed, the other open) are lettered for reference. 168. Each valve f is similar to the other, and opens in the same direction; its gudgeons moving freely in sockets fixed to the sides of the annulus nearest the axis. 169. Their working gear is as follows:-a is a small hollow protuberance, or bonnet, screwed on the annulus and communicating with the inside of it; on one of its inner sides is a socket, on the opposide side a stuffing box; one end of a spindle works in the socket, the other passes through the stuffing box to the outside of the bonnet; to this end is attached the lever b, and to the centre is attached the lever c, both levers being at right angles with the spindle and in the opposite direction to each other. To the extremity of c is attached, by a moveable joint, the rod d, and to the extremity of b is fixed the weight e, being more than sufficient to counterpoise f, which is connected with it by means of a moveable joint at the other end of and attached to the centre of f. The levers are so placed as to cause f to be hal open when they point to the axis. Thus it is evident that during the revolutions of the roke, two of the valves f on its ascending side, denoted by the arrow, will by the mere preponderance of e be shut, and the whole of the others will be open, as represented in fig. 1. 170. For more easily comprehending the action of these valves, let it be considered that their movements are regulated by the mere gravity of e. It will be afterwards shown that they are regulated with more precision by means of the catch h and lever m. Let it also for the present be considered that there are no valves i, nor lever k, their use will afterwards be detailed. The machinery to which motion is to be imparted is attached to that end of the axis next fig. 1. K 2 |