| Number. | Size in inches. |
|---|---|
| 0 | 0.340 |
| 1 | .300 |
| 2 | .284 |
| 3 | .259 |
| 4 | .238 |
| 5 | .220 |
| 6 | .203 |
| 7 | .180 |
| 8 | .105 |
| 9 | .148 |
| 10 | .134 |
| 11 | .120 |
| 12 | .100 |
| 13 | .095 |
| 14 | .083 |
| 15 | .072 |
| 16 | .065 |
| 17 | .058 |
| 18 | .049 |
| 19 | .042 |
| 20 | .035 |
| 21 | .032 |
| 22 | .028 |
| 23 | .025 |
| 24 | .022 |
| 25 | .020 |
| 26 | .018 |
| 27 | .016 |
| 28 | .014 |
| 29 | .013 |
| 30 | .012 |
E.
LOCOMOTIVE BOILERS.
If the ideas of Clark and Overman are correct, the value of vertical flues with the water inside, as compared with horizontal flues with water outside, is comparatively as follows: One half of the surface of the horizontal tube (the upper half) is available, but this half generates steam twice as fast as the same area of upright tube surface. Thus the amount of evaporation will be the same in either position, for the same absolute tube surface, not considering the increased diameter by applying the heat to the outside, or the advantage, so highly estimated by Overman, of applying the heat to the convex surface.
The following application of Montgomery’s vertical flue boiler to the locomotive engine for heat generation and application, seems to satisfy nearly all requirements. Retaining the original furnace shell, produce it forwards so that it shall just clear the driving axle, let the sides drop to within two feet of the rail, and close up the bottom. Next, inside of this place a rectangular box which shall be a continuation of the inner box, the top being about nine inches above the diametric chord of the semicircular crown, leaving a water space of three or four inches between the sides and bottom of the two boxes. Fill the inner box with vertical tubes, the top and bottom being flue plates, the tubes being screwed in at one end and fitted with a screw thimble at the other, may be removed for cleaning at any time and will effectually stay the inner box against the enormous pressure upon the top and bottom. The pressure being inside of the tubes will tend to keep the end joints tight, where, in the common boiler, the reverse is the case.
That the burning gases may retain sufficient heat to burn until they are discharged, there should be less tube surface at the back than at the front end, a requirement which is easily satisfied by decreasing the number and increasing the size of tubes from the front to the back end. In the common boiler the ferrule area being less than the flue area, a stronger blast is used than is really necessary to draw the hot gases through the tubes, while in the vertical tube boiler the gas area may be equally large at all points.
Again, any amount of oxygen may be applied to the gases at any point of their passage from the furnace to the smoke box, by the admission of fresh air to any part of the barrel. Thus the advantage of a combustion chamber (if there is any) is obtained without the sacrifice of a single inch of heating surface, as we only require to admit air between the tubes and not into them; this may be done either by hollow stay bolts or by larger openings, to be open or shut at pleasure.
If the gases in passing through the boiler are left to themselves, we get, without an effort, the effect produced by Montgomery’s third claim, namely, the application of the heat to the upper half of the tubes; and, however we wish to apply the passing heat to the flues, complete control over the motion of the gases may be had by the use of a Venetian blind damper in the smoke box, in two parts; the upper and the lower parts moving independently, allow us to throw the heat upon any part of the length of the tubes. Of course, by heating most the upper part of the flues, we stand a better chance of getting circulation.
It might be objected that so much flat boiler surface would give a form more liable to explosion than the circular barrel. Experiments lately made by William Fairbairn, (England,) induced by the bursting of a locomotive fire box, show that the flat surfaces are the strongest forms of the boiler, or, to use his own words, “are conclusive as to the superior strength of flat surfaces as compared with the top, or even the cylindrical parts of the boiler.” His experiments show that two plates one fourth and three eighths inch thick, connected by screw stay bolts four inches from centre to centre, will resist over one thousand lbs. per square inch.
By such a plan of engine we may always have any amount of heating surface with a moderate sized boiler, and a low centre of gravity.
The excess of cost of the engine, above described, over the common form would be about $500, the annual interest of which is $30, which must be saved by the new plan, (say ten cords of wood).