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“the direction of its aperture, and the water in the tube P (which will of course “ be at the general level of the water in the boiler,) will not be so subject to “ agitation*.'
To test the idea that the foam which issues through the gauge-cock is produced by a rush of steam towards the aperture, and the method, proposed by Mr. Ewbank, for lessening it, tin pipes, ten inches and three-eighths in length, and three-eighths of an inch in diameter, with seventy-nine perforations, each about two hundredths of an inch in diameter, were attached to the central and lowest gauge-cocks b and c, Plate 1. When the level of the water within was about five-eighths of an inch below the cock c, or nearly two inches and four-tenths below the cock b, on opening the lowest cock, the steam being at a pressure of two atmospheres and two-tenths, a very little water mixed with the steam, passed through the opening of the cock; on opening the middle cock b, water and steam flowed through c; on closing this and opening the highest cock a, less water issued through c. When both a and b were opened, the water flowed copiously through c. At the close of this experiment, the glass water-gauge showed that the level of the water within the boiler was one inch below the lowest cock, In another experiment the water being one inch and a half below the lowest
a cock; c being opened, no water issued; c and b being opened, a very little water issued through c; a, b and c, being opened, a little water was mixed with the steam.
The facts thus elicited, are in accordance with the preceding observations of the committee in relation to the general foaming which takes place when an aperture is made in any part of the boiler. The great respect which they entertain for the ingenious author of this device, on account of the valuable contributions which he has made to them, induced them to give this full trial of his suggestion.
The third form of apparatus would cut off the access of water from the general foaming, until it reached the level of the lowest apertures; but it would substitute a local foaming which would effectually, if not equally, prevent the true hydrostatic level from being indicated: in this respect it is nearly equivalent to the gauge-cock, already described, as applied to the water-gauge.
The various floats which have been applied to show the level of the water within a boiler are well known. They have never obtained favour in this country, and are considered particularly objectionable in their application to the high pressure boiler, on account of the motion within. The stuffing-box, commonly used to pass the index-rod of the float through the top of the boiler, is objectionable, and different devices have been originated with a view to remedy this difficulty. That of Mr. Thomas Ewbank, of New York, described in volume 16, of the Journal of the Franklin Institute, is highly ingenious, and is reported by him to have stood the test of experience in his small boiler, producing steam of rather less than five atmospheres. The apparatus of the committee did not furnish facilities for a proper trial of this float; and besides, such a trial would be inadequate to test its use in practice.
A float serving to give an alarm by the issuing of steam, was made the subject of a few experiments, and answered well, as far as those trials went. Long use, however, could alone determine, perfectly, the peculiar liabilities to derangement in this apparatus. The float alluded to is shown on Plate 4, fig.
* Journal of the Franklin Institute, vol. 10, pp. 80, 81, 1832. “ Supplement to the communication of Thomas Ewbank, Esq. of New York, to the Com. on Explosions."
A. The requisite buoyancy is given to the metallic pyramid, a, which is solad, by the weight b, acting as a counterpoise over the fulcrum c. The whole apparatus is attached to the top of the boiler by the screw d, and the nut e, and the working parts are thus entirely within the boiler. When the water is at the proper level f g, the shoulders h and i are in the same horizontal line, and the disks k l, which are pressed against the shoulders by two springs shown in the figure, close the apertures k m, and I n, which, when open, permit steam to escape from the boiler. Should the water sink below its proper level, the equilibrium of the pyramid a, being destroyed, the shoulder i, would press against the disk 1, remove it from the aperture, and permit steam to escape through l n; should the water, on the contrary, rise above the proper level, steam would escape through k m. The force of the springs which close these openings, should, of course, be duly proportioned, as they will determine the sensibility of the apparatus. The details of construction are clearly shown in the figure, which is drawn to a scale. *
The quantity of steam which would escape by the small opening I n, while it would serve as an alarm, would not materially diminish the supply of water within the boiler. The float used by the committee, was found to be sensible to less than three-tenths of an inch in the change of level : it could have been made more sensitive by increasing the breadth between the shoulders, so as to bring them in contact with the disks, as shown in the figure.
Effect of Foaming on the Elasticity of the Steam within the Boiler.
This point was the next proposed for examination. When an opening is made in a boiler, of which the sides are heated, will the effect be to diminish the elasticity of the steam within, by permitting its escape, or will the water thrown upon the heated sides by the foaming which results, be converted so rapidly into steam as actually to increase the elasticity of the vapour within ? It is obviously difficult to obtain an answer to a query involving so many con. ditions. It might be expected, however, that a small boiler would afford satisfactory means of making a fair trial of the question, since the size of the openings could be varied very easily, so as to make them comparatively small, or very great. The position of the boiler used by the committee in its furnace was such, that the sides could be very readily heated; thus placing it in favourable circumstances to increase the elasticity of the steam by producing a foaming within. The apparatus was therefore adapted to make the desired trial.
M. Arago, in his Essay on the Explosions of Steam-Boilers, states, that MM. Tabareau and Rey, at Lyons, found on opening a large stop-cock, connected with a small high pressure boiler, that the safety valve rose, showing an increase of pressure within. The boiler was placed naked upon a fire of charcoal, and the part not containing water was surrounded by flame. The experiments of MM. Arago and Dulong, at Paris, were attended with a contrary result, the opening of a safety valve being always accompanied by a diminution in the elasticity of the steam within. The circumstances, however, were not the same as those in the experiment of MM. Tabareau and Rey.
To repeat this experiment, a hot fire was made beneath the boiler, and when the water had fallen to about three inches above the lowest line of the cylinder, the experiment was commenced, the pressure being about three atmospheres and a half. A stop-cock of .03 sq. inches in area, 10 booth part of the area of the water surface at the beginning of the experiment, delivering per second, at three
* In the figure, the shoulders h and i, do not rise high enough; they should overlap the disks more, that no depression or elevation of the water may carry them clear of the disks.
and a half atmospheres, about four hundred and nine cubic inches of steam was first opened; next the safety valve was raised, either in part or entirely, the area when entirely raised, being .208 sq. inches, or To'sgths of the water surface, and capable of delivering, in one second, at three and a half atmospheres, a bulk of steam nearly nine times that of the steam chamber. The water level falling by the waste caused in the experiments, the steam soon became surcharged with heat; and the iron of the boiler, from near the water line to more than one-third of the distance from the lowest line to the middle of the convex surface, became, on each side of the water line, heated until it attained redness, passing, of course, through the temperature of maximum vaporization of the water thrown by the foaming, upon the iron. The experiments were made at intervals, until all the water was exhausted. Water was then injected in small quantities, and with the bottom of the boiler for the most part red hot, the trials were repeated.
It will be seen from the following table, that the result was uniformly a diminished elasticity of the steam within, as shown by the fall of the mercury in the steam gauge. The pressures varied, in the former part of the experiments, from three and a half to eight atmospheres.
The first column of the table contains remarks referring to the level of the water within the boiler. The second to the opening made. The third is the temperature indicated by the thermometer, M, Plate 1, before referred to, as passing nearly to the bottom of the boiler. The fourth, the height of the mercury gauge, before making the opening. The fifth, the height immediately after making the opening, unless the contrary is stated in the sixth column, which contains remarks relating to the effect on the gauge. The seventh column contains general remarks.
The thermometer at first indicated the temperature of the water, then that of the surcharged steam, and finally was affected by the heat radiated from the bottom of the boiler.
3 inches, Gauge-cock, 2843 18.6 18.0
air in gauge, 80° Do. 20.4 20.2
ponding to 18.6 Safety valve, 20.5 20.0 Fall very rapid. inches, 3) atmos
ponding to 21.3 .9 of an inch, Gauge-cock, 317321.9 21.8
inches, 54 atmos. Safety valve, 22.1 21.7 Fall in f second. Do. 22.6 20.6 Fall in 2 seconds. From about 8}
to 5 atmospheres. .9 inch nearly, Stop-cock, 380
bottom rapidly inSafety valve, 4681|15.1 12.6
creasing in heat.
supply thrown in 16.0 14.0 Sudden descent. Thermometer rose