Imágenes de página

In some cases the expansion-valve is worked by the governor acting on the cam, as in Maudsley's and Whitelaw's engines. We here give diagrams explanatory of a “self-regulating motion for expansion-valves,” the invention of Mr. Howson of Manchester.

In referring to the drawings, fig. 98 is a general view of the apparatus. Figs. 99 and 100 are enlarged views of tappet-rod and levers, showing the different positions they assume: а is a case or nozzle containing a common

[ocr errors][merged small][merged small][merged small][merged small][merged small]

equilibrium or double-beat valve, through which the steam is admitted through the pipe i in connection with the boiler to the cylinder; v is the valve-spindle, u its guide; g a lever for lifting the valve, having its fulcrum on the pillar b secured to the nozzle; c is a tappet-rod, having an upward and downward motion, and actuated by any suitable means from the motion of the crank-shaft, taking care that for one stroke of the piston there are two of the tappet-rod. A recess or slot d is cut in the tappet-rod c

. for the reception of the lever e, which has its upper end supplied with a notch & and a projection or stopping-piece e. The lower tail of the lever e

w forms an inclined plane f, which, when required, is allowed to come in contact with and slide against the adjustable stud m. This stud projects from the upper tail of the double lever h, which has its fulcrum on a pillar fixed to the nozzle, the lower tail being furnished with a series of teeth forming the segment of an ordinary worm-wheel ; into this gears the worm n, keyed in the shaft or spindle o. On the same shaft is the bevil-pinion P, which gears into the bevil-wheel q fixed to a second shaft, to which a partially rotary motion is communicated by the governor-rod r and lever w. The operation of the machinery is as follows: The engine being in motion, and the tappet-rod c at the extent of its upward stroke, the valve will be down, and the levers c and e in the position shown at figs. 99 and 100; but on its descent, the notch x on the lever e will come in contact with the point of the lever g, thereby raising the valve. On the further descent of the tappet-rod, the lower end or inclined plane of the lever e slides against the stud m, and has a tendency to throw the former into the position shown at fig. 10. The lever g having its point then released from the notch x, the valve drops by its own weight, and, consequently, the supply of steam is cut off from the cylinder, the lever g assuming its former position as at figs. 8 and 9. On the return or upward stroke of the rod c, the upper part of the notch x sliding against and passing over the rounded or under part of the lever g, immediately assumes its proper position, preparatory to its making another descent. In order to prevent noise as much as possible, the projection e, which prevents the notch < from taking too great a hold on the lever g, is furnished with a small leather buffer. The variable motion obtained from the centrifugal force of the governor-balls through the action of the governor-rod r, lever w, wheel and pinion q and P,

and worm n, communicates a like variable motion to the lever h, and, consequently, to its projecting stud m. It will now be easily perceived that the inclined plane f on the lever e will come in contact with and slide against the stud at different positions in the descent of the rod c, and the valve have varied lengths of time for remaining open; and consequently, varied quantities of steam will be admitted to the cylinder, according to the variations of the governor. The vibratory motion required for the stud m is so small, and the means for effecting it so powerful, that the most trifling alteration in the action of the governor will be communicated to the stud m; while the adoption of the worm and segment will form an infallible and solid bearing for the pressure of the inclined plane,

[ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small]

Fig. 101 is a sketch in which the governor connection is dispensed with altogether; the stud m being adjusted by hand to a bracket fixed to the nozzle, the side of the slot in the bracket having a scale to which an index on the stud may be pointed, in order that the engineer may at once place it in a position that the steam may be cut off at the particular portion of the stroke required.

The piston-rod, in moving up and down through the cylinder-cover, is kept steam-tight by what is called stuffing-box.” This is shown in fig. 102: a a is part of the cylinder-cover; a cylindrical hollow cup or box is cast on this of a much larger diameter than the piston-rod bb; this is curved inwards, as shown in the diagram; the aperture in the cylinder-cover is a little larger than the piston-rod, to admit of its easy working; packing, composed of plaited hemp, is wound tightly round the piston-rod bb, at the part ee; the stuffing-box"cover" nn is placed above this packing, and screwed tightly down by the screws.



The piston, as originally made by Watt, was kept tight by hempen packing; metallic pistons are now almost universally used. That known as Goodfellow's is extensively used in Lancashire. In fig. 103 we give a transverse section of this : aa is the body of the piston, with shoulder turned on it at e; an annular ring o is placed loosely round the piston;

[ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small]

a plan of this ring is shown in fig. 104; this is turned eccentrically, and worked on its edge ; this gives a uniformity of action to the whole circumference: its upper and lower edges are bevilled, as shown in fig. 106 ; these bevils bear or press against other rings nn, the interior of which are similarly bevilled, as shown in fig. 105. The outer springs nn are

[blocks in formation]



accurately ground to the upper and lower plates m and c, and the whole secured by the screw-bolts as shown. The outer rings nn are kept pressed against the cylinder by the action of the internal ring oo lying loosely on the plate c. These diagrams will sufficiently explain the peculiarity of a metallic piston ; for notices and illustrations of other varieties we must refer the reader to other and larger works.

We have already illustrated the mode of connection of condenser and cylinder, and the condensation by a jet of water admitted to the condenser ; in fig. 107 we give a sectional diagram of an improved form of injectionvalve for condensers introduced by Mr. Cowper, and described by him at the Institution of Mechanical Engineers. The object of this valve “ to maintain the full pressure of the water at the point of entrance into the condenser, and to obtain a more efficient distribution of the jet of water, without danger of getting it choked.” In the diagram, fig. 107, a is the condenser, 6 the eduction-pipe leading from the cylinder, c the air-pump, d the cold water cistern in which they are immersed ; the injection-valve is a conical one, rising a little above the bottom of the condenser, with a perforated cup below in the cistern. As shown in the drawing, the valve is lifted up by the screwed rod; and the injection-water can be regulated with the utmost nicety. The water enters the condenser in a fine sheet all round the valve, which sticks to the sides of the condenser, and fills the whole space with a fine spray. Mr. Cowper has also modified the airpump; the bottom drops into a well, as in the drawing, in the bottom of the condenser, and the water rises up the space when the air-pump bucket


fig. 107.

fig. 108. dips into it, forming a water-valve instead of the ordinary foot-valve, and giving pressure enough to insure the bucket-valve opening if there was any obstruction.

In place of passing the steam into a receptacle, and being condensed by coming in contact with cold water, in other forms of condensers, as Hall's, the steam is passed down a series of copper-pipes externally surrounded with cold water; the condensed water falling into a box beneath, from which it is pumped away.

By this arrangement the water used for raising steam can be again returned to the boiler. Mr. Pirson, of America, has recently introduced a condenser known as the “ Fresh Water Condenser."

The peculiar feature of this condenser, which distinguishes it from all others previously known to the public, is the placing of the condensing tubes horizontally within the ordinary shower-condenser, which is made of enlarged dimensions for the purpose. By this arrangement, the water required for condensation is admitted through the ordinary injection-cock, and rises to the top of the external condenser; where it is discharged on a scattering-plate, from whence it passes directly on to the tubes of the internal condenser, which are below it, and arranged in three ranges or sets, one above the other. The steam from the cylinder is admitted into the upper range, and passes through the three before being discharged at the bottom. The fresh water produced by the condensation of the steam is pumped out by a small pump, and immediately returned to the boilers; while the water used to produce condensation is taken out by the air-pump of the engine. The internal condenser is not attached to the external one, but merely laid in it. The three ranges are separately made, and the outlet from the upper slips loosely into the one below it; so that when the whole internal condenser is together, it may be moved from one-eighth of an inch to one-fourth of an inch in any direction. This freedom prevents any liability to fracture from unequal expansion; and the tubes being in vacuum relieves them from all pressure. As the condensing water reaches the bottom of the tubes, it is immediately pumped out; so that there is not at any time any water around the tube other than the thin sheet passing over


their surfaces. On the Osprey, the vacuum within the tube of the internal condenser is twenty-six inches, and the same in the external one; the internal vacuum is the result of condensation, while the external vacuum is produced by the air-pump. The Osprey has made three passages, or 2,750 miles in all, and has no trouble in keeping a full supply of fresh water in her boilers. This condenser has been used with considerable success on board the above-named vessel. Our account is extracted from a paper read by Mr. Bartol, at a late meeting of the Franklin Institute of Philadelphia

Mr. Siemans, of Birmingham, an engineer well known for his ingenious inventions, has recently introduced a form of condenser highly spoken of, and known as the “Regenerative Condenser.” At a meeting of the Institution of Mechanical Engineers, Mr. Siemans stated that the origin of this condenser was a suggestion to the author, by Mr. Graham of Mayfield Works, “ to recover the heat from the condensing in the form of a reduced amount of boiling hot water.” It consists of an upright rectangular trunk, a, of cast-iron, the lower end of which is cylindrical, and contains a working piston, b, which performs two strokes for each one of the engine. In the trunk is a set of copper plates, C, upright and parallel to each other; the intervening spaces being the same as the thickness of the plates, viz. between 1th and 16th of an inch.

The upper extremity of the condenser, fig. 108, communicates on the side, d, to the exhaust-port of the engine; and on the other, through a valve, e, to the hot well. The plates are fastened together by five or more thin bolts, with small distance washers between each plate. There is a lid at the top of the trunk, by removing which the set of plates can be lifted out. Immediately below the plates the injection-pipe enters.

The action of the condenser is as follows: Motion is given to the piston. At the moment that the exhaust-port of the engine opens, the plates are completely immersed in water; a little of which has entered the passage above the plates, and is, together with the air present, carried off by the rush of steam into the hot well, the excess of steam escaping into the atmosphere. The water then, in consequence of the downward motion of the piston, recedes between the plates, exposing them gradually to the steam, which condenses on them. Their upper edges, emerging first from the receding water, are surrounded by steam of atmospheric pressure, and become rapidly heated to about 210°. The immersion of the plates still continuing, the steam is constantly brought into contact with fresh cool surface, by which the greater portion of it is condensed ; until, as the piston descends, the injection enters, and completes the vacuum. This is done by the time the working of the piston of the engine has accomplished one-seventh of its stroke. The upper extremities of the plates become heated to near 210°, and the lower to about 160°.

Taking the initial temperature of the condensing water at 60°, the final temperature at 210°, the latent heat of steam at 2120 960 units, the quantity of water required is 6 6 lbs. to condense 1 lb. of steam of atmospheric pres

The common injection condenser (supposing the temperature of the condensed steam to be 110o) requires 21.2 lbs. in place of 6.6 lbs.

In fig. 109 we give a drawing of the ordinary vacuum gauge, used in connection with condensers in order to ascertain the degree of vacuum attained. The mercury is contained in a cast-iron cup open to the atmo


« AnteriorContinuar »