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ARTICLE VI.
OF THE MEANS OF APPLYING STEAM.
Supposing that no doubt can now remain in the mind of the intelligent reader, of our being able to work with steam of power equal to 120 pounds to the inch, with great advantage and safety, we will proceed to consider of the most economical means of using or applying this power, so that it may produce the greatest effects.
The engine may be constructed similar to that of Bolton
and Watts, except the gears for working the valves, which should be so arranged
as to open the valve, when the piston is up, to let in a puff of the strong
steam to drive it down, but to shut again as soon as enough has got in,
which, when suffered to expand, will fill the cylinder with atmospheric
power only; the steam entering the cylinder with a power of 120 pounds to
the inch, drives the piston with great force; but the valve being shut at
1/8 part of the stroke, the steam expands and decreases in power, all the
rest of the stroke,
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to the end, where it should just balance the atmosphere when another valve opens to let in a similar puff of steam to drive the piston up again; while other valves open to let the steam escape from before the piston. Thus the piston is driven by strong puffs of steam, the same as an air-gun drives its bullets; with this difference, the air-gun is soon exhausted, but the fire keeps up the power of the steam; the whole power of the steam is expended on the piston, before it leaves the cylinder, except what is necessary to resist the atmosphere. This is supposing the engine to work without a condenser.
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A TABLE.
Showing the proper time to shut off the steam, according to the power
in the boiler; and how the power and load it will carry at every part of
the stroke diminishes, in order that the steam may spend all its power;
supposing the lengths of the stroke divided into eight equal parts, and
working without a condenser.
| Power of steam in the boiler, 120 pounds to the inch | Load, deducting 15 pounds for the resistance of the atmosphere. | Power of steam in the boiler 60 pounds to the inch. | Load, deducting 15 pounds for the resistance of the atmosphere. | Power of steam in the boiler 30 pounds to the inch. | Load, deducting 15 pounds for the resistance of the atmosphere | Power of steam in the boiler 15 pounds to the inch. | Load | |
| 1 | 120 | 105 | 60 | 45 | 30 | 15 | 15 | 0 |
| 2 | 60 | 45 | 60 | 45 | 30 | 15 | 15 | 0 |
| 3 | 45 | 30 | 45 | 30 | 30 | 15 | 15 | 0 |
| 30 | 15 | 30 | 15 | 30 | 15 | 15 | 0 | |
| 5 | 26.25 | 11.25 | 26.25 | 11.25 | 26.25 | 11.25 | 15 | 0 |
| 6 | 22.5 | 7.5 | 22.5 | 7.5 | 22.5 | 7.5 | 15 | 0 |
| 7 | 18.25 | 3.25 | 18.25 | 3.25 | 18.25 | 3.25 | 15 | 0 |
| 8 | 15 | 0 | 15 | 0 | 15 | 0 | 15 | 0 |
| 52.5 | 22.5 | 7.5 | 0 | |||||
| 269.5/8 | 179.5/8 | 89.5/8 | 0 | |||||
| 33.7 | 22.4 | 11.2 | 0* | |||||
| 15 | 15 | 15 | 15 | |||||
| 48.7 | 37.4 | 26.2 | 15** |
*Average load without a condenser.
**Average load with a condenser
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The foregoing table is founded on the supposition that the elastic power of steam is governed by the same laws, which govern the elastic power of permanent elastic fluids, viz. That their elasticity is in the inverse proportion with the space they occupy; or, as their density, called the Boylean law, (article 4.) If compressed into half the space their power is doubled, and if expanded into double space, their power is reduced to one half. But this is not strictly true with steam, because it is not a permanent elastic fluid. There will not as much heat enter into 1/8 part of the cylinder, with steam of 120 pounds to the inch elastic power, as will he sufficient to cause it to expand to fill the whole cylinder with elastic power, equal to 15 pounds to the inch, to resist the atmosphere (see article 4); it will not bear, therefore, to he shut off so soon. If a sufficient quantity of steam be admitted, to contain heat to expand it to fill the cylinder with power equal to the resistance of the atmosphere, the average load of the stroke will be greater than is shown by the table.
When the steam is 120 pounds to the inch, as in No.1 of the table, by the law it requires to be shut off at 1/8 part of the stroke, to give the steam time and room to spend all its power in driving the piston to the end, and to fill the cylinder with steam, equal to 15 pounds to the inch, just sufficient to resist the atmosphere the effective load being always 15 pounds less than the power of the steam, diminishes from 105 pounds to the inch, the load when the valve shuts, to 0 at the end of the stroke.
To find the average load or the load the steam will carry
the whole stroke, and resist the atmosphere, add
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the different loads at each division together, and to that sum (for the deficiency that is occasioned by not dividing the stroke into an infinite number of divisions) add half the load at the time the valve was shut, that is half of 105 pounds, equal to 52 5/10 pounds, and it makes 269.5 for the effect of the stroke; which divided by 8, the number of divisions, and it quotes 33.7 pounds, the average load; to which add 15 pounds and it makes 48.7 pounds the average load, when a condenser is used to take off the resistance of the atmosphere.
When the steam is 60 pounds to the inch power, as in No.2, in the table, it requires to be shut off at 2/8 of the stroke, and the average load against the atmosphere is 22.4 pounds to the inch, and with a condenser, 37.4 pounds.
When 30 pounds to the inch power, as No. 3, it requires to be shut off at 4/8 of the stroke, the average load against the atmosphere being 11.2 pounds to the inch and with a condenser 26.2 pounds. And when the steam is 15 pounds to the inch power, as No. 4, it requires to be shut off at the end of the stroke, the average load against the atmosphere being 0, and with a condenser of 15 pounds to the inch.
Now it is evident that, as the cylinder is to be filled
with steam in each case, just equal in power to the resistance of the atmosphere,
or equal to 15 pounds to the inch, therefore it contains an equal quantity
of heat in each case; although die effects are so different, that when we
work without a condenser, the strong elastic steam, 120 pounds to the inch,
carries a load of 33.7 pounds to the inch; while steam of 60 pounds power,
carries but 22.4 pounds; steam of 30 pounds carries
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11.2 pounds, and steam of 15 pounds carries 0, above the resistance of the atmosphere, and with a condenser to take off that resistance, the loads are 48.7, 37.4, 26.2 and 15 pounds to the inch, by the law of permanent elastic fluids on which the table is founded. But as it has been shown (article 4) that strong elastic steam does not contain heat in proportion to its power compared with steam less elastic; it is probable that in No. 1 the valve must be kept open ~ of the stroke, which would increase the average load to about 80 pounds to the inch; so that it appears that on this new principle, by confining the steam until its elastic power rises to 120 pounds to the inch, we can produce about 6 times the effect from equal quantities of heat, that can be produced, if we use it with power equal to 15 pounds. And if this be done with equal quantities of heat drawn from the boiler, we may conclude that nearly equal quantities of fuel will be used in each case, because the compression of the strong elastic steam on the surface of the water in the boiler, creates no obstacle to the heat passing from the fire into the water, but rather facilitates it; because solid bodies receive heat more freely than porous ones.
Suppose the cylinder requires to be filled 1/3 part with
steam of 120 pounds to the inch, to admit heat sufficient to expand the
steam to fill the cylinder with a power equal to 15 pounds to the inch,
and divide the cylinder into 9 parts, then by the principles laid down,
the load at the end of the several divisions, will be nearly as follows,
when we use a condenser.
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| 1 | 120 |
| 2 | 120 |
| 3 | 120 |
| 4 | 100 |
| 5 | 80 |
| 6 | 40 |
| 7 | 34 |
| 8 | 27 |
| 9 | 15 |
| 10 | 60 Half the power when shut off |
| 11 | 716/9 |
79.55 pounds, the average load being more than six times
the load of the old principle, which is not above 12 pounds. This is effected
by drawing from the boiler an equal quantity of heat at each stroke, in
each case. This however is a mere inference drawn from the premises supposing
that a vacuum has a greater capacity for receiving heat than a plenum, (see
art. 4.)