to contain water, set in brick work like a common copper, with a
fire-place _r_ underneath it, having a chimney _s_. The boiler thus
constructed, is intended to afford the means of producing steam: and
if we conceive two casks or strong hollow vessels of any form to be
placed under the surface of the water, near the boiler, as at _t_
and _v_, and that each of these vessels has a valve opening into it
in its lower part as _u_ _u_, and two pipes _w_ _w_, proceeding from
the upper part of the vessels to the top of the steam boiler _q_,
while two other pipes _x_ _x_ proceed from the lower parts of these
vessels into a cistern _y_, forty feet above the level of the water;
an apparatus thus constructed will nearly form the water-commanding
engine, for if the vessels _t_ and _v_ are both filled with water
by the valves _u_ _u_, and the cock _z_ be opened after the steam
has accumulated in the boiler, the elastic fluid thus generated will
instantly rush down into the vessel _t_, and when the surface of the
water is heated expel the whole of its contents up the pipe _a x_,
into the cistern _y_, where it will be retained by a valve opening
upwards in any part of that pipe, as at _a_. This done, the cock _z_
must be shut, and after permitting the steam to accumulate for a
short time, that at _b_ must be opened, and the steam will rush into
the vessel _v_ and perform a similar office, _c_ being the valve to
prevent the return of the water. When the steam is shut off from the
vessel _t_, the elastic fluid which had previously been introduced
to expel the water, will be condensed by the cold media round it,
and thus a vacuum will be produced in the vessel _t_, consequently
a part of the water in which it is immersed will rush into it by the
valve _u_, and occupy the whole internal cavity, thus putting it
in a state of preparation for a second opening of the cock _z_, by
which its contents will be again discharged into the cistern _y_,
and so of the two vessels alternately; for while _v_ is emptying,
_t_ will be filling, and vice versâ, which agrees with the Marquis's
account when he says, "that the man is but to turn two cocks, that
one vessel of water being consumed, another begins to force," &c.
The above suggestion for an engine capable of raising water may be
still further improved by adding a suction pipe to the valves _u_
_u_, and the pressure of the atmosphere will increase the working
power of the engine more than thirty feet: and should a less height
be required, the forcing pipe may be shortened in a proportionate
degree: indeed this fact was attended to by the next person who
claims the honour of having invented the steam-engine, to which it
may now be adviseable to direct the reader's attention.
[Illustration]
The engine suggested by Savery for the purpose of raising water,
consisted of a boiler _a_ furnished with a safety valve _v_. The
steam-vessel _r_ was connected with the well H, by a suction pipe
_n_; and when water was to be raised the vessel _r_ was filled
with steam, which rushing in, soon expelled the air: when that was
completely effected, the communication with the boiler was closed,
and the steam condensed, which diminishing its bulk, formed a
vacuous space within the vessel; the pressure of atmosphere then
operating upon the surface of the water in the well, drove it up the
pipe. In this form of the apparatus, the inventor was seldom able to
raise water more than thirty feet: and when a greater altitude was
required, it was effected by the impellent force of high pressure
steam. This was accomplished by the ascending pipe _k_, which was
sometimes carried sixty feet higher than the steam-vessel _s_; and
a reference to the great expansive force of steam will show that
this operation must be attended with considerable danger. After
condensing the steam and filling the vessel _r_ with water, a new
supply of steam was then introduced, which pressing on the surface
of the water, drove it up the pipe _k_; and it will be evident
that the pressure on the internal surface of the boiler must be
proportioned to the height of the column of water thus raised by the
steam.
The principal objection to this form of the engine arises from the
great consumption of fuel, a considerable portion of the caloric
employed in the generation of the steam being absorbed in heating
the new surface of cold water last raised from the well; and where
great heights are required, there appears no mode of completely
obviating this objection. Should it, however, be required merely
to raise water about thirty feet, there are few contrivances more
economical or better adapted for general use.
While speaking of Savery's apparatus it may be adviseable to
notice the very ingenious adaptation of the same principle to
the construction of a _gas engine_, by Mr. Brown. In the latter
case a vacuum is formed by the introduction of an inflamed jet of
carburetted hydrogen gas, which consumes the oxygen, and rarefies
the nitrogen, by the increase of temperature which ensues. The
vacuum thus produced is much more perfect than would at first view
have been supposed, from the nature of the process resorted to by
the patentee; but the economy of employing carburetted hydrogen
gas as a substitute for condensible vapour is still somewhat
problematic.[10]
[10] Since writing the above, the Editor has seen a report on Mr.
Brown's engine by Professor Millington, in which it is distinctly
stated that the apparatus is fully adapted to the purpose for which
it is intended.
To more fully understand the nature of Mr. Brown's engine, it may be
better to revert to a diagram, which will sufficiently explain its
general principles.
[Illustration]
In the above view, the cylinders _c_ and _d_, are the vessels in
which a vacuum is alternately effected; _g i g_ and _h j h_ are
two pipes, leading into the lower cylinders _x_ _x_, shewn in the
next page, from which the water rises along those pipes to fill the
vacuum cylinders alternately. The water thus supplied is discharged
through the pipes B into the tank or trough _z_, where it falls upon
the overshot water-wheel, and, by the rotatory motion thus produced,
gives power to such machinery as may be connected to it. The
water runs from the wheel along a case surrounding the lower half,
into a reservoir _v_, from which the lower cylinders _x_ _x_, are
alternately supplied.
The gas is supplied to the cylinders by the pipes _k_ _k_ _k_, which
must be, of course, attached to a gasometer, or some other reservoir
of gas. The gas also passes along the small pipe _l_ _l_ (which
communicates also with the gasometer), and being lighted at both
ends of that pipe, is kept constantly burning in order to ignite the
gas within the cylinders.
The gas being admitted along the pipe _k_, the flame from the pipe
_l_ is now freely communicated to the gas in the cylinder, through
the orifice, by the opening of the sliding valve _s_, which is
raised by the arm _r_, lifted by the rod _o_ by means of the beam.
The water in the reservoir _v_ passing down one of the pipes _w_,
into one of the lower cylinders _x_, causes the float _y_ in that
cylinder to rise, and, pushing up the rod _o_, raises the end _b_ of
the beam, which, of course, draws up with it the cap _f_, and forces
down the cap _e_ of the other cylinder _c_.
[Illustration]
The _alternate_ action of each cylinder is produced by chains
and rods, attached to a glass or iron vessel _p_, more than half
filled with mercury, and turning upon a pivot; each end receives
its movements of elevation and depression from the rise and fall
of the projecting arms _q_, by the action of the beam above; the
mercury within flowing to the lower end, giving an impetus, and thus
regulating the supply of gas to the cylinders, and the movement
of the slide in the trough _v_. By this action the water from the
reservoir flows down the pipe _w_, into the vessel _x_, and produces
the elevation of the float _y_ and the rod _n_, and raises the cap
_e_ by the ascent of the beam at _a_.
The motion thus produced in one part of the machinery, operates upon
the corresponding parts on the other side, and hence a corresponding
motion is obtained: the slider in the trough _v_, moved by the
action of the mercurial tube _p_, being removed from its position,
allows the water to fall into the other pipe _w_; and, as it
ascends, suffers the float _y_ to descend, and rising into the main
cylinder, then lifts again the beam at _b_, and its connexions, and
forces down the cap _e_ on the top of the other cylinder.
When the vacuum is produced in the cylinders, the air must be
admitted to allow the water to be discharged, and the caps to be
raised: this is effected by a sliding valve in the air-pipe _m_
_m_, acted upon by chains _t_ _t_, attached to the floats in the
reservoir, and as motion is given to them, the valve is made to
fly backwards and forwards, so as to allow the free admission of
atmospheric air.
Chains _u_ _u_, with suspended weights, open the cocks in the pipe
_k_ _k_, and produce the alternate flow of the gas, and regulate and
modify its supply. In the pipes _g_ _i_ _g_, and _h_ _j_ _h_, are
clacks to prevent the return of the water, when the air is admitted
into the cylinders.
A piston may be worked as is above described, with the machinery
attached; but it may also be worked in a distinct vessel so as to
communicate with several cylinders, and, consequently, several
pistons may work at the same time, the air and vacuum valves being
opened and closed by similar means to those adapted to work the
induction and eduction valves of steam-engines.
The atmospheric engine comes next in order, and its claim to
practical utility is of a very early date.
[Illustration]
The cylinder _b_, is in this engine placed over a boiler _n_,
and if we suppose the piston _p_ made to fit air-tight, it will
be evident, that it must be driven up by the action of the steam
beneath, should a sufficient supply of heat be applied; when this
is effected, the condensible vapour may be reduced to its original
bulk, by the introduction of water from the cistern _i_. In the
working engine however, the ascent of the piston is effected by the
action of the lever _e g_, acting on the fulcrum _f_. To the end
_g_ of this lever or working beam is attached the pump-rod _h_, and
it will be evident that whenever that preponderates over the piston
_p_, that the latter must be drawn up. On the readmission of the
steam, a new supply of condensing water is introduced by turning
the cock _l_, and the pressure of the atmosphere above the piston
being unbalanced by any resistance beneath, the end _e_ is again
depressed, and the pump-rod again elevated. The pipe _g_ is employed
to carry off the condensing water, which would otherwise accumulate
within the cylinder; and the small forcing pump, with its rod _v s_,
supplies the condensing cistern _i_, by the pipe _t_.
At the beginning of the last century, the atmospheric engine
had made considerable progress in the mining districts, and in
1718, the patentees agreed to erect an engine for the owners of a
colliery, in the county of Durham, where several hundred horses had
previously been employed. Mr. Henry Beighton, who was engaged as
an agent in this concern, materially improved the engine by making
it self-acting, and divesting it of nearly all the complicated
machinery, which had been previously employed for that purpose.
A very simple and at the same time ingenious mode of illustrating
the operations of an atmospheric steam-engine will be found in the
annexed apparatus, suggested by Professor Brande, and employed in
his lectures at the London Institution.
[Illustration]
The glass tube and bulb _b_ is shewn with its piston _a_, the rod
being hollow and closed by a screw _c_. If steam be generated by
the spirit lamp _d_, the air will speedily be expelled, and after
this is effected, the screw _c_ may be closed, and a working stroke
produced by artificial condensation.
We come now to a new and distinct era in the history of this
important invention, and in noticing the labours of Mr. Watt, we
may almost speak of his engine as the gigantic offspring of a hand
giving birth to an automaton, no less powerful than that of the
fabled enchanters of the olden time.
Mr. Watt's first great improvement in the engine of Newcomen may
be best understood by reference to the annexed diagram, in which
_a_ represents the cylinder, and _b_ its plug or piston made to fit
air-tight. The pipe _d_ is furnished with a stop-cock, by means of
which the elastic vapour is occasionally admitted.--A similar pipe,
furnished with a stop-cock at _f_, passes from the other side of
the cylinder, and enters the vessel _g_; _e_ being the reservoir to
contain water.
[Illustration]
If we now suppose the piston at the bottom of the cylinder, and
steam admitted by the pipe _d_, its expansive force will elevate
the piston, and when the air is expelled, the whole internal cavity
of the tube will be filled with condensible vapour. On closing
the steam-cock, and opening that connected with the vessel _g_, a
portion of the vapour will immediately expand itself, and coming
in contact with the cold sides of the vessel, a portion of its
heat must be absorbed by the water at _e_. A new portion of steam
then descends, and is also condensed, and indeed the same process
continues till the whole of the steam is drawn from the tube. A
vacuum being thus formed, the pressure of the atmosphere will
preponderate, and the piston rod be depressed to the bottom of
the tube. On closing the stop-cock _f_, a new supply of steam may
be admitted by the other pipe, and after raising the piston, the
process of condensation may be readily repeated.
The advantages that arise from this mode of forming a vacuum are
very considerable, not the least important of which, is a saving of
nearly half the fuel.
In the old engine, the condensing water must reduce the temperature
of the internal surface of the cylinder to that of the atmosphere,
before a vacuum could be produced, and when the condensing water
was applied more sparingly, the elastic vapour remaining in the
cylinder was found to materially reduce the pressure of the air
operating above. From this it will be seen that the great advantage
of Mr. Watt's apparatus consists in performing the condensation in
a separate vessel, so that the cylinder is always preserved at the
temperature of boiling water.
Having thus produced a vacuum without the intervention of condensing
water beneath the piston, Mr. Watt's next improvement consisted
in closing the top of the cylinder, so that the piston-rod worked
through an air-tight hole in the centre of the cap; and to ensure
the necessary pressure within the cylinder, steam with an elastic
force greater than that of the atmosphere was admitted above the
piston. The atmospheric engine of Newcomen was thus converted into a
steam-engine, and its power was easily regulated.
A cylinder and piston constructed on the most improved principles
may now be examined.
[Illustration]
In the annexed diagram, the cylinder A is furnished with a
steam-tight piston, the rod of which is supposed to be connected
with the working beam. B represents the pipe which admits the steam
from the boiler, the quantity being regulated by the throttle valve
_c_, and the elastic vapour is now passing through the box _d_ _d_,
so that it enters beneath the piston. At the same instant of time,
a communication is formed through the aperture _m_ _n_ to the pipe
_p_, which leads to the condenser. When the piston reaches the top
of the cylinder, the sliding bridge or valve has its direction
changed, so that the pipe _r_, and consequently the bottom of the
cylinder, is connected with the condenser, while a passage is opened
from the pipe _m_ _n_ to the steam box. Thus a communication is
alternately made between the top and bottom of the piston.
The slide-valve represented above is not invariably employed in
the double-acting engines, and we frequently find the annexed
contrivance resorted to, in some of the best engines.
[Illustration]
The pipe 14 represents the passage to the cylinder, and a
communication is now opened with the steam chamber _g_. The raised
valve is perforated and a similar valve beneath closed by the rod
which passes through it. On closing the valve _g_, the lower valve
_h_ is opened, and a free passage between the condensing pipe
beneath and the upper part of the cylinder is the result. If we now
suppose a similar double valve placed at the bottom of the cylinder,
it will easily be seen that an effect similar to that described in
the sliding valve will be produced.
The speed of the engine is regulated by a very ingenious contrivance
introduced by Mr. Watt, called the _governor_, and represented
beneath.
[Illustration]
The balls _i_ _i_ are supported by the bent levers _h_ _f_, and
as they are made to revolve with the fly wheel axis, by means of
a band passing round the pulley _c_, any increase in the speed of
the engine will cause the balls to diverge. The moment this takes
place, the shorter arm of the lever _n_ is depressed, and as the
extremity _l_ is connected with the steam-pipe by the throttle
valve, the supply of steam must of necessity be diminished, and the
speed of the engine reduced.
As the working power of the engine depends very materially on the
accurate fitting of the piston, it may be adviseable to examine some
of the modes of effecting this important object.
Mr. Smeaton, who greatly improved the atmospheric engine, coated the
under side of the piston with elm or beech planks about two inches
thick; the wooden bottom being screwed to the iron with a double
thickness of flannel and tar, to exclude the air between the iron
and the wood. By the adoption of this improvement, its property of
conducting heat was reduced, and the wood having been previously
jointed, with the grain radiating in all directions from the centre,
was not liable to expand by the heated steam. This piston was kept
air-tight by a small stream of water continually falling on its
upper surface; but in Mr. Watt's engine he was compelled to make
the piston fit tight without any other media than the oil that was
employed to lubricate it.
The piston is now cast with a projecting rim at bottom, which is
fitted as accurately as possible; the part above the rim being about
four inches less than the cylinder, thus leaving a circular groove
for the hemp which forms the packing. To keep this in its place, a
lid or cover is put over the top of the piston, with a projection
which enters into the circular groove for the packing, and pressing
upon it, the plate is forced down by screws, which work into the
body of the piston. By this means the packing is made to fill the
internal part of the cylinder with tolerable accuracy, and thus
prevents for a time any steam passing between the piston and the
cylinder. When, however, by continued working, the packing ceases to
fit, it occasions a waste of steam, to remedy which, the cylinder
cap must be removed, and as this is attended with a considerable
degree of trouble to the engine-man, it is seldom attended to till
a considerable loss of power has arisen. There are two improvements
on the piston, by which this inconvenience is to a certain extent
obviated.
In the first, by Mr. Woolfs, each of the screws is furnished with
a wheel or nut, and these are all connected together by means of a
central wheel, working loose upon the piston-rod in such a manner,
that if any one of the screws be turned, a similar motion is given
to the remainder.
[Illustration]
In a piston thus constructed, there is little difficulty in drawing
down the packing, by applying a key to the square head of the
projecting screw, employed to communicate with the rest: the
key-hole being afterwards closed by a cap.
The second contrivance is by Mr. Barton, a diagram of which,
accompanied by a piston as it is usually constructed, is shewn
beneath.
[Illustration]
In the first piston, the screws _i_ _i_ are made to compress the
packing _h_ _h_, by acting upon the plate _n_ _n_, the piston-rod
_r_ being firmly attached by the nut _c_.
In one of the modifications of _Barton's piston_, on the contrary,
the packing is dispensed with, as the flexible springs _t_ _t_ _t_
press upon the wedges _c_ _c_ _c_, and expand the intermediate
plates. A break-joint is readily formed, by making the series of
plates double; the second set of plates falling upon the spaces
which occur between the first row.
The action of the _high pressure_ engine depends upon the great
elastic force acquired by steam, when exposed to the action of heat
at very high temperatures.--It may indeed be considered as a return
to the principle of Brancas and the Marquis of Worcester, as in
this engine no condensing water is necessary; and it acts merely
by the elastic or repellant force of steam. In the high pressure
engine, the condenser is taken away; and the steam, instead of
being converted into water by artificial cold in a close vessel, is
allowed to escape into the atmosphere from one side of the piston,
while it is acting forcibly on the other.
The advantages of the high pressure engine over that used with a
condenser, are cheapness in construction, and a saving of the whole
expense attendant on procuring a sufficient supply of condensing
water, which in some cases is an object of considerable importance.
[Illustration]
In the annexed section, the piston _B_ passes through an air-tight
stuffing box, and the steam is entering beneath it, by the four-way
cock _E_. If we now suppose the piston at the top of the cylinder,
a new arrangement of the communicating pipe takes place, as the
steam which was beneath escapes, while a fresh supply enters above.
The four-way cock may be best explained by a section in the opposite
direction. Two pipes are seen at the lower extremity of the cock,
which communicate with the upper and under sides of the piston. The
aperture _D_ opens to the air, while the pipe _C_ serves for the
admission of steam from the boiler.
[Illustration]
We have now to notice the double cylinder engine constructed by
Woolfs, which will be found, by reference to the diagram in the
preceding page, to consist of a high pressure cylinder, connected
with a condensing apparatus.
A and B represent the two cylinders, in the larger of which the
steam is allowed to expand itself, after passing from the high
pressure cylinder B. The steam, which in the first instance is of
considerable elasticity, is admitted to the cylinder B, by the tube
and valve E, and entering the cylinder above its piston, impels it
to the bottom. When this is effected, a communication is opened
between the upper part of the cylinder B, and the under side of
the cylinder A. The communication between the cylinder B and the
steam-pipe E, is now reversed, and the steam is made to press on
the under side of the piston B, a communication being at the same
time formed between the upper part of the cylinder A, and the pipe
leading to the condenser which is seen beneath. So that if we
suppose the two pistons connected by means of their rods with one
end of an ordinary working beam, the upward and downward strokes of
each will be performed at the same time. We have hitherto considered
the steam as passing direct from the boiler to the cylinder B;
this, however, is in reality effected by a more circuitous route,
as it is in the first instance admitted to the steam-case of the
larger cylinder by the pipe C, and passing round a similar case,
encircling the cylinder B, it is then made to enter at E. The pipe
at D is merely intended to form a communication for carrying back to
the boiler any water that may be produced by condensation in the
steam-case, before the engine arrives at a proper temperature for
working.
Having thus briefly examined the nature of Mr. Woolf's engine, it
may now be advisable to revert to the boiler, by which he proposes
to generate steam of sufficient elasticity for the use of the
small cylinder, which requires elastic vapour of great expansive
force. The boiler, represented by the diagram beneath, consists of
a series of tubes, of cast-iron, connected by screw-bolts with the
under side of a larger vessel A A, communicating with the engine.
The upper boiler is furnished with four, and in some cases, with
five apertures; the first of which is intended for the admission
of water, to supply the waste which continually arises from
evaporation. The safety valves, man-hole, and water-pipe are also
shewn.
[Illustration]
The mode of setting this boiler is also of considerable importance,
as it is advisable to give a long and waving course to the chimney.
[Illustration]
A A still represents the principal boiler, while the figures 1, 2,
3, &c. indicate the passage of the flame and heated air; a section
of the chimney being shewn at O.
The steel-yard safety-valve which was employed in all the early
engines is simple, and the nature of its construction may readily be
understood. A represents a portion of the upper part of the boiler;
B the safety-valve or plug made to fit air-tight on the valve-seat
beneath; C the lever working on its axis at D, and furnished with a
moveable weight E, adjusted to balance the pressure of steam within
the boiler.
[Illustration]