_Gas Holder._
The name of gas holder, or, as it is improperly called, gasometer, is
given to the vessel employed for collecting the gas and storing it up
for use. In the principle and construction of this part of the gas light
machinery, peculiarly valuable improvements have of late been made. They
have contributed to lessen the expence of the apparatus so much, that a
reservoir for storing up any quantity of gas, may now be furnished for
nearly one half the sum which such a vessel cost as originally
constructed.
In the infancy of the art of lighting with coal gas, the reservoir was
encumbered with a heavy appendage of chains, wheel-work and balance
weights, and from the construction of the machine, it was necessary to
guard it from the impulse of the wind, the action of which on the gas
holder, would have rendered the lights which the machine supplied with
gas, unsteady.
Hence it was necessary to inclose the gas holder in a building, called
the gasometer house, which formed one of the largest items of
expenditure which the proprietor of a gas light establishment was called
upon to defray.
Now, however, the whole of these expensive appendages is dispensed with,
nor is the gasometer house to contain the gas holder any longer
necessary, and the machine as now constructed may be fixed in the open
air.
_Gas Holder as originally employed._
The gas holder, of the original construction, consists of two principal
parts; first, of a cistern or reservoir of water, usually constructed of
masonry, or of cast-iron plates, bolted and screwed together; and
secondly, of an air-tight vessel which is closed at top and open at
bottom, inverted with its open end downwards into the cistern of water.
This vessel is always made of sheet-iron plates rivetted together
air-tight, and was suspended by a chain or chains, passing over wheels,
supported by a frame work.
If the common air be allowed to escape from the inner vessel, when its
open end is under the edge of the water in the outer cistern, it will
freely descend, and water will occupy the place of the air; but if the
avenue of the escape be stopped, and air be made to pass through the
water, the suspended inverted vessel will rise to make room for the air.
And, again, if the suspended vessel be counterpoised by a weight, so as
to allow it to be a little heavier than the quantity of water which it
displaces, it will descend, if, the entering gas be withdrawn through an
outlet made in the vessel to permit the gas to escape. But if the outlet
be stopped, and air again be admitted under the vessel, it will rise
again. The apparatus, therefore, is not only a reservoir for storing up
the gas introduced into it, but serves to expel the gas which it
contains, when required, into the pipes and mains connected with this
machine.
According to this construction of the apparatus the interior inverted
vessel forms strictly what is termed the gas holder. It is suspended as
already stated in the outer cistern, by a chain or chains, passing over
pullies, supported by blocks and frame work, and to the chain there is
affixed a counterpoise balance, of such a relative weight, as to allow
the gas holder a slow descent into the water, in order to propel the gas
into the mains or vessel destined to receive it, with a very small and
uniform weight.
It will be obvious, that when a gas holder of this construction becomes
immersed in the water, it loses as much of its weight as is equal to the
bulk of water which it displaces, and hence to render its descent
uniform, and to preserve the gas within, of an invariable density, at
any degree of immersion, a greater counterpoise is required as the gas
holder rises out of the water.
Among various methods which have been adopted to attain this object, the
ends of the chains by which the gas holder is suspended, have been
fastened in separate grooves, in the edge of a large wheel or pulley, of
such a diameter, that the gas holder rises to its full height, before
the wheel makes one revolution.
In another groove in the edge of the same wheel, was fixed the end of
another chain, to which a balance weight was suspended. This weight was
made nearly equal to the weight of the gas holder. To equalize the
density of the gas within the gas holder, at any degree of immersion of
the vessel, the weight chain was made to pass over a wheel, furnished
with a spiral groove, so as to make the radii of the wheel, change
reciprocally with the relative weight of the gas holder, and
consequently to render the pressure of the gas holder constant and
uniform.
Another and more elegant method of obtaining an uniform elasticity of
the gas within the gas holder, and which has been more generally
adopted, consists in passing the chain or chains by which the gas holder
is suspended over a pully or wheels, and making the weight of that
portion of the chain, which is equal to the depth of the gas holder, or
that part of it which becomes immersed into the water, equal to one
half of the weight of the specific gravity of the gas holder.
It is obvious that before the purified gas can be admitted into the gas
holder, the vessel must be allowed to descend to the bottom of the
exterior cistern, in order to get rid of the common air which it
contains. This may be effected rapidly by opening the _man hole_ at the
top of the gas holder, to cause the vessel to descend completely into
the outer cistern filled with water. The man hole is then screwed up
again air-tight, and the machine is ready to receive the gas. It is
obvious that the operation of opening the man hole for letting out the
common air, requires only to be done once prior to the commencing of the
working of the apparatus.
_Gas Holder with Governor, or Regulating Gauge, lately brought into
use._
It must be obvious that the gas holder, of which a description has been
given in the preceding page, requires a machinery at once ponderous and
very delicate, qualities not easily reconciled in the construction of
such a machine. It is necessary that the specific gravity apparatus, or
regulating chain, wheel work and balance weight, should be constructed
so correctly as never to suffer the gas within the vessel, to alter its
elasticity. The machinery requires an expensive framing for its support,
and independently of this, the gas holder must be inclosed in a
building, in order to protect it from the impulse of the wind, the
action of which would render the lights supplied from the apparatus
unsteady, as already stated. The expensive and cumbersome specific
gravity apparatus has been wholly superseded by an ingenious contrivance
called the regulator or governor. The action of this machine, for which
we are indebted to Mr. Clegg, is, that it regulates the density of the
gas prior to its entering into the mains, to any required degree,
whatever its density may be in the gas holder.
To accomplish this object, the apparatus through which the gas passes
into the mains, is provided with an aperture which is capable of being
enlarged or diminished by a very slight force. To effect this object the
gas is made to enter a small vessel, and then to pass through a
regulating aperture, the capacity of which becomes enlarged or
diminished by the velocity of the gas to a certain standard. If the
pressure of the gas in the gas holder becomes increased, the regulating
aperture through which the gas passes into the mains, becomes
diminished, in such a proportion, that the velocity with which the gas
issues into the mains, remains constant and uniform. And on the other
hand, if the pressure of the gas in the gas holder becomes diminished,
the regulating aperture of the governor becomes enlarged to effect the
intended regulation.
The following is a concise description of the manner in which this
instrument is constructed.
_A_, _B_, _C_, _D_, fig. 9, pl. III. is a hollow cylindrical vessel, or
the outer case of the machine. It is made of sheet iron or copper,
japanned within and without, closed at the top and bottom. It is placed
between the gas holder and the mains, into which the gas is to be
conveyed. _a_, _x_, is a pipe which proceeds from the outer vessel and
branches upwards in the centre of the base of the outer vessel A, B, C,
D. It brings the purified gas into the governor. _b_, T, is the outlet
pipe which conveys the gas from the governor into the mains. It is
placed above the inlet pipe and communicates with the interior vessel.
G, H, a short projecting hollow cylinder, which proceeds downwards from
the centre of the base of the outer case of the machine A, B, C, D. _u_,
_x_, _y_, _z_, is the regulator, properly so called; it consists of a
small conical vessel, also made of sheet iron or copper, closed at the
top and open at bottom, japanned within and without. This vessel rises
and falls vertically in the outer cylindrical case. A, B, C, D, of the
machine, when the latter is filled with water. It is kept steady in its
motion by two slender guide rods, as shewn in the sketch.
Between the inlet pipe which conveys the gas into the governor, and the
outlet pipe which conveys the gas into the mains, is fixed horizontally
a partition plate, having a circular aperture in the centre. This plate
is seen between the letters _x_, T.
Through this orifice passes a perpendicular axis P, which is fixed at
the top in the centre of the regulator or interior floating vessel _u_,
_x_, _y_, _z_.
The interior extremity of the axis P, is furnished with a cone, having
its base downwards, and projecting beyond the pipe _a_, _x_, into the
short cylinder G, H. The base of this cone slightly exceeds the diameter
of the orifice _x_, T, so as to close up entirely, when the regulator is
raised to its greatest height in the outer vessel A, B, C, D. But when
the floating vessel _u_, _x_, _y_, _z_, descends in the outer vessel A,
B, C, the vertex of the adjusting cone P, is just entering the aperture.
The regulator is conical, and its form is in exact proportion to the
loss of the weight of water which it displaces; so that the gas conveyed
into it always retains an invariable density at whatever height the
regulator may be immersed in the water in the outer vessel. If the outer
vessel be filled with water up to the top of the central branch pipe,
the interior vessel will float, and the water will stand in the outer
vessel at the same height as in the inside of the regulator; hence the
density of the gas within will be the same as the outer air. But the
density of the gas in the regulator may be increased at pleasure by
applying a weight to the top of the regulator, the water will then stand
higher on the outside of the regulator than within, and this adjustment
will remain uniform, because the quantity of matter of the regulator is
in the ratio of its specific gravity or loss of weight as it becomes
immersed in the water.
Let us suppose that the pipe above the partition plate be connected with
a main, and that the outlet pipe below the partition plate be connected
with a gas holder supplying gas into the machine; it will be evident
that if the density of the gas in the inlet pipe becomes by any means
increased, a greater quantity of gas must pass betwixt the sides of the
adjusting cone and the aperture in the partition plate, the consequence
of which will be that the floating regulator will rise, and therefore
contract the area of the partition plate. And if, on the contrary, the
gas in the inlet pipe decreases in density the regulator will descend,
so that whatever density the gas may at any time assume in the gas
holders or mains, its density in the floating vessel _u_, _x_, _y_, _z_,
will remain uniform, and consequently the velocity of the gas passing
into the mains will be regular.
For when the aperture of the partition plate would admit more gas than
what is necessary for the density of the gas in the mains, the floating
regulator rises, and by that means raises the adjusting cone to diminish
the aperture in the partition plate, and when, on the contrary, the
aperture does not allow a sufficient quantity of gas to come from the
gas holders, the gas passes out of the regulator into the mains, and in
so doing the regulator descends, and consequently the adjusting cone
increases the opening to admit the requisite gas into the mains.
The further application of this machine, for regulating the height of
the gas flames issuing from burners or lamps of different kinds will be
shewn hereafter.
_Gas Holder with Governor or Regulating Guage at the Gas Works Chester._
Fig. 7, plate VI., exhibits a perpendicular section of the gas holder at
Chester. A, A, are wooden beams or pillars fixed into sockets or shafts
constructed on the outside of the brick-work, and descending as seen in
the design to the depth of the tank. There are four of these pillars,
three only are seen in the section. B, B, are round iron guide rods
rendered steady by stays at the upper extremity of the rods.
To the upper and lower edges of the gas holder are fastened eye bolts,
C, C, through which the guide rods, B, B, are inserted, so that the gas
holder must move steadily and firmly. D, E, are the inlet and outlet
pipes which convey the gas into and out of the gas holder.
F, F, are diagonal stays for supporting the roof of the gas holder,
which has a slope of ten feet from the centre to the circumference. G,
is the wooden curb at the lower margin of the machine.
This gas holder is circular. It measures forty-eight feet in diameter,
and thirteen feet in height; its weight is eight tons.
The regulator adapted to this gas holder, measures three feet across its
base, and its height is three feet three inches. The base of the
regulating cone is four inches, and its length two feet. The machine is
made of sheet iron japanned within and without.
_Gas Holder with Governor or Regulating Guage at the Birmingham Gas
Works._
The construction of this gas holder, as exhibited plate V., fig. 2,
shows a perpendicular section, and fig. 3, a plan of the machine; _a_,
_a_, _a_, _a_, fig. 3, are upright pillars, two of which B, B, are seen
in the section, fig. 2.
In the centre of the gas holder is fixed a pipe, which allows the gas
holder to slide on the central guide rod G, made fast at the bottom of
the cistern, and at the top of the cross framing. C, C, are diagonal
stays; D, the inlet pipe which conveys the gas into the gas holder E;
the outlet pipe F, the wooden curb.
The capacity of this gas holder is 30,000 cubic feet; its regulator is
precisely similar to that before described. The weight of the gas
holder, exclusive of the wooden curbs at top and bottom, is between
eight and nine tons.[39]
[39] The gas holder without specific gravity apparatus, at the Bristol
Gas Works, is constructed on a similar principle. Its capacity is
43,000 cubic feet. Its regulator is like those already described.
The gas holder thus disencumbered of its specific gravity apparatus,
requires no building to enclose it, it may be erected in the open air,
for the machine cannot suffer from the rain or snow falling upon it, nor
can the action of the wind render the lights unsteady.
The saving which has been effected by these improvements is very great.
A gas holder without balance weight and specific gravity apparatus, with
its governor, may be erected complete for action, for little more than
half the cost that would be required for the erection of an apparatus of
the same capacity constructed on the old plan.
The cheapest house constructed of sheet iron to surround a circular gas
holder of 15,000 cubic feet capacity, supposing the surface of its
cistern or tank to be level with the ground, costs no less than £. 320.
The balance weights and chains £. 60, and the cast-iron framing for
supporting the specific gravity machinery £. 150.
The cost of a gas holder of the before-mentioned capacity, will be £.
300, and a cast-iron tank for it, £. 800.--If the tank be constructed of
brick-work, it will cost about £. 500, and if of wood (an iron-bound
vat,) it will cost £. 600.
A governor or regulating guage adapted to a gas holder of from 10,000 to
40,000 cubic feet capacity, costs £. 50. In the construction of the gas
holders, as hitherto described, it is always advisable when the
situation will admit it, that the diameter to the height of the machine
should be in the proportion as three to two. If these dimensions be
observed, and the gas holder is not burdened by iron stays, it will not
displace a column of water more than one inch and a half in height. And
by adapting to the machine, a governor or regulating guage, a
considerable saving will be effected. The gas holder may then be
constructed as shown fig. 7, plate VI., or fig. 2, plate V. A circular
gas holder of 30,000 cubic feet capacity, if properly constructed,
weighs no more than eight or nine tons, including its wooden curb at its
lowest extremity, and its diagonal stays.[40]
[40] Mr. Lee of Manchester supplies his house, two miles distance from
the manufactory, by means of a portable gas holder.[41] A small
carriage upon springs conveys two square close gas holders made of
wrought iron plates, and each containing fifty cubic feet of perfectly
purified gas, equivalent together to about six pounds of tallow. Each
gas holder weighs about 160 pounds; and has a valve at the bottom,
which is opened by the upright main pipe, the moment the gas holder is
immersed in the pit. The strength of one man is found sufficient for
the labour of removing the gas holder from the carriage to its place.
[41] Henry’s Experiments on the Gas from Coal, in the Memoirs of the
Manchester Literary and Philosophical Society, 1819.
The roof of the machine ought to be constructed of thicker sheet iron
than those forming its sides. The only object of the balance weight, is
to counterpoise the weight of the chain of the gas holder of the old
construction, so that when the gas holder is wholly immersed in the
cistern, the chain and balance weight are in equilibrium, deducting the
required pressure with which the gas holder is intended to act. And this
ought never to exceed from half an inch to an inch perpendicular _head_
of water.
The sheet iron best adapted for constructing gas holders, is that known
in commerce as No. 16, wire guage.[42] Gas holders made of plates of
iron of this kind, have now been in use for upwards of nine years, and
are not in the least injured or decayed. Self-interested views may
sometimes lead unprincipled workmen to make use of sheet iron plates of
a much greater thickness, but experience has sufficiently shown that any
greater thickness than what has been specified is wholly unnecessary,
and only serves as a drawback to the facility of the general operation.
[42] A superficial foot weighs three pounds.
_Revolving Gas Holder at the Westminster Gas Works._
The revolving gas holder is an ingenious contrivance invented by Mr.
Clegg, for storing large quantities of gas. A gas holder of this
construction may be erected with advantage in situations where the
nature of the ground will not admit of a deep cistern either above or
below the ground being constructed, without an enormous expence.
The base which it occupies is no larger than what would be required for
a gas holder of equal capacity, built on the plan of the gas holders of
which descriptions have been just given.
It regulates its own specific gravity. And though more expensive in the
construction, yet as it does not require a deep cistern, like the
machines already described, it can be erected at the same cost. The
revolving gas holder is exhibited, fig. 8, plate VI. Its capacity is
15,000 cubic feet; it weighs 12 tons. Plate I., (on the title page,)
exhibits a perpendicular section of the gas holder.
On inspecting fig. 8, plate VI., it will be seen that this machine is
the segment of a hollow cylinder, or broad wheel, formed by two
concentric cylindric surfaces of 250° each, revolving upon an horizontal
axis, and supported upon a wooden frame or truss, in a brick cistern, I,
K, L.
The extremity C, D, fig. 8, plate VI., or C, plate I., of the segment of
the cylinder, is open, and the other extremity A, is closed. E, is a
balance pipe, which connects the closed with the open extremity of the
machine.
This pipe is made of such a weight as to counterpoise the interval
between the open and closed end of the gas holder, so that the machine
may move in a segment of a circle equally, in whatever position it may
happen to be placed, and hence the gas will be discharged from the gas
holder with an uniform velocity.
The balance pipe E, is closed at the part where the letter E is placed;
H, is a straight pipe, which forms the communication between the
balance pipe E, and the horizontal axis upon which the machine moves.
This axis is hollow: it is supported by stays and braces, as shown in
the design on the title page. The cistern in which the gas holder moves
is 7¹⁄₂ feet deep. It must be evident that the gas being conveyed into
the open end of the hollow axis, it will pass through the pipe H, into
the balance pipe E, and this being stopped up near E, the gas will
proceed into the closed end of the gas holder. The operation will
therefore be as follows:
Let us suppose the closed extremity of the machine to be at the surface
of the water in the cistern, and the gas flowing through the axis as
described, the extremity of the machine will begin to fill, and
consequently to ascend; the gas holder will therefore continue to move
upon its axis until the open end C, D, fig. 8, plate VI., or C, plate
I., comes nearly to the surface of the water, and when the gas is
required to be discharged, it will return through the same channel by
which it entered. A sufficient pressure is given to this gas holder for
discharging the gas at the velocity required, by means of a weight
suspended to one extremity of a chain, passing over a pulley, whilst
the other end is fastened into the groove of a small circle attached to
the stays of the machine, as shown in the designs. The circle is
graduated to express the capacity of the machine. Thus any degree of
pressure may be given to the gas, and the gas holder will retrograde in
an arc describing 270° of a circle, as the gas becomes discharged, until
the end A, again arrives at the surface of the water.
The small curved pipe T, plate I., serves to let the common air escape
out of the angular extremity of the machine, whilst filling with gas,
when the margin of this part of the machine becomes immersed in the
water, and to let the common air enter again, when the gas holder is
discharging its contents.
S, plate I., is a friction sector, upon which the axis of the machine
revolves. The advantage of this contrivance is, that the friction is
very much diminished. The length of the friction sector is eight feet,
the diameter of the gudgeon or axis four inches; therefore the space
described by its outer circumference and its centre is in the proportion
of 96 to 4.
_Rule for finding the capacity of a Revolving Gas Holder of given
dimensions._
To find the capacity of a revolving gas holder, of given dimensions,
take the area of the whole diameter, then the area of the inner
cylinder, multiply the difference by the length, and from this deduct
one-fourth.
_Collapsing Gas Holder._
The collapsing gas holder is a still farther improvement by Mr. Clegg,
on this part of the gas light apparatus, and certainly of all the
contrivances which have been invented for collecting and storing up
large quantities of gas, this machine must be pronounced to be by far
the most simple, economical, and efficient. The striking advantage of
the revolving gas holder which we have just been describing is, that it
enables the dimensions of the tank to be very much diminished, where the
nature of the ground will not admit of a cistern of great depth being
sunk, except at an extraordinary expence; but the still superior feature
of the collapsing gas holder which we now come to describe, is, that it
may be constructed of any required capacity, and adapted to a tank or
cistern of such diminished depth, as scarcely to deserve that name. It
requires a sheet of water no more than 18 inches in height, so that it
may be constructed in or upon ground of all descriptions, not only with
every possible facility, but at an immense saving of expence.
Fig. 1, plate VII., exhibits a perspective view of this gas holder. It
is composed of[43] two quadrangular side plates joined to two end
plates, meeting together at top in a ridge, like the roof of a house.
The side and end plates are united together by air tight hinges, and the
joints are covered with leather, to allow the side plates to fold
together and to open in the manner of a portfolio. The bottom edges of
the gas holder are immersed in a shallow cistern of water, to confine
the gas. By the opening out or closing up of the sides and ends of the
gas holder, its internal capacity is enlarged or diminished, and this
variation of capacity is effected without a deep tank of water to
immerse the whole gas holder in, as required in the ordinary
construction of rising and falling gas holders. The collapsing gas
holder requires therefore only a very shallow trough of water to immerse
the bottom edges of the gas holder to prevent the escape of the gas
introduced into it. The lower edges of the gas holder which dip in water
are made to move in an horizontal plane or nearly so, when they are
opened, so that they dip very little deeper in the water when shut or
folded together, than when opened out.
[43] From Mr. Clegg’s specification--the same letters of reference
indicate the same parts in all the designs.
For this purpose the top or ridge joints which unite the two sides of
the gas holder, are slightly raised up when the sides close or approach
together, or slightly depressed when the sides open out or recede from
each other. To guide the whole gas holder in this movement, two
perpendicular rods rise from the bottom of the shallow tank which pass
through sockets in the ridge joints at the upper part of the gas holder.
These sockets are secured by collars of leather round the shafts or
rods, to prevent the escape of the gas, and they are braced by chains
proceeding from their upper extremities and fastened at the ground on
each side of the tank.
The weight of the gas holder is balanced by levers bent in the form of
the letter L, and placed inside of the gas holder. These levers move on
centre pins fixed at the bottom of the shallow trough, which pass
through the angles of the L levers. The perpendicular arms of the levers
are jointed at their upper extremities to the sides of the gas holder,
nearly in the middle. At the ends of the horizontal arms of the L
levers, are weights to counterbalance the weights of the gas holder, and
both sides of the gasholder are provided with these kind of levers,
which at the same time that they balance its weight cause the ridge
joint of the machine to rise and fall, as before described, so that the
under edges of the gasholder, which are immersed in the water to confine
the gas, must move in an horizontal plane instead of describing an arc
of a circle as they would do if the ridge joint was a fixed centre of
motion.
When the gas holder is closed the perpendicular arms of the levers stand
nearly in a perpendicular position, but when the gas holder is opened
out the levers become inclined. And as they move upon a fixed fulcrum at
their lower extremities, and are jointed to the sides of the gas holder
at their upper extremities, they allow the whole of the gas holder to
descend gradually upon the guide rods, nearly in the same degree as the
lower edges would rise up if the ridge joint was stable, and if the
sides described an arc of a circle.
It is obvious, however, that the latter movement is not very essential,
but it is convenient and necessary to make a very inconsiderable depth
of water in the trough or tank serve the purpose it is intended. It may
be also observed that the sides of the collapsing gas holder may be made
to unfold or open on a fixed ridge point as a centre of motion, but it
will then require a considerable depth of water in the tank to keep the
lower edges of the sides and ends of the machine always beneath the
surface of the water, because the sides of the gas holder then describe
an arc of a circle when they are open. Fig. 1, plate VII., is a
perspective view of the apparatus, as it appears when partly filled with
gas. Fig. 2, plate VI., exhibits a perpendicular longitudinal section
made through the middle of the gas holder and tank; fig. 3, plate VI.,
represents a transverse section; fig. 4, plate VI., is an end view of
the machine, and fig. 5, exhibits an horizontal plan or section of part
of the gas holder, or one of its ends, to show how the end plates are
jointed together, and the leather applied to prevent the escape of the
gas.
A, fig. 2, is the inlet pipe which conveys the gas into the machine, it
rises up perpendicularly through the water in the tank, high enough to
prevent the water entering it. B, is the exit pipe for discharging the
gas into the mains from the gas holder. It rises up nearly to the top of
the machine. C, C, are the guide rods, they are firmly fixed at their
lower extremities into a cast-iron framing D, D, beneath the bottom of
the tank. The upper ends of these rods are kept steady by chains E, E,
fig. 3, and fig. 4, descending on each side of the gas holder, and
fastened at bottom to D, D, part of the same iron framing. F, G, K, K,
are the balance (or L) levers which suspend or bear up the gas holders;
they move on fixed centre pins supported in pieces _a_, _a_, fig. 2, and
3, of the framing D. The upper end of the perpendicular arms are jointed
to the iron bars H, H, H, see fig. 2, which are riveted to the side
plates of the gas holder; they are united by knuckle joints W, fig. 6,
which allow the sides of the machine to approach each other till they
come together. The arms _i_, _i_, of the bent levers F, G, K, K, fig. 4,
are placed nearly at right angles to the other arms F, G, fig. 3, and
the extremities of the arms _i_, _i_, are loaded with counterpoise
weights K, K, which always tend to bring the arms F, G, into a vertical
position, and consequently to close up the sides of the gas holder, in
order to expel the gas through the exit pipe B, fig. 2.
Three pairs of the above mentioned L levers are represented in fig. 2,
in the length of the gas holder to support it in different parts and to
prevent it altering its figure. The weight that must be used is
according to the magnitude of the machine. The pairs of levers F, G, K,
K, fig. 3, are placed side by side on the same centre pins, and cross
each other. K, K, are counterpoises at the ends of the arms _i_, _i_,
they are long pieces of iron extending from one lever K, to the next
lever. The tank is furnished at the bottom with a recess, as seen in
fig. 3, and 4, to allow the arms _i_, _i_, and counterpoises K, K, to
descend beneath the edges of the gas holder. In the course of the
movement of the machine, the sides of the gas holder are shorter at the
top or ridge joints than at the bottom edges, as seen in fig. 2, in
order that the under edges of the folding ends can move in an horizontal
plane. Each of the folding ends is made of two triangular plates,
connected together by an air tight joint, and each plate is again
jointed to its respective side plate, and they are made tight by
introducing a piece of leather or oil-cloth, or any other flexible
substance impervious to air in the angle at the joint.
Fig. 5, represents the end plates of the gas holder when nearly
extended, but when it is closed up, the two parts N, O, of the end
assume the position as shewn by dotted lines. L, M, fig. 5, shews how
the ends of the two side plates are turned outwards at _b_, to render
them stiff and firm. As all the flexible joints are made strong by
metallic joints or hinges, the leather has no stress to bear but only to
prevent the escape of the gas; R, R, fig. 2, are the collars of leather
to prevent the escape of the gas at the openings in the top or ridge
joint where the guide rods _c_, _c_, pass through.
The tank must be filled with water to such a level that the under edges
of the sides and ends of the gas holder will be a few inches immersed in
the water. The counterpoises K, K, fig. 3, tend to close the sides of
the machine together, and expel the gas from the gas holder through the
pipe B, fig. 2. The counterpoises are so adjusted in weight as to force
out the gas with the requisite pressure.
If more gas be introduced by the pipe A, it distends the sides of the
machine and moves them outwards upon the ridge joint. A man hole, as
seen at S, fig. 2, is made in each side of the gas holder, to give
entrance when any repairs are necessary, or to oil or examine the
joining leathers. It is scarcely necessary to add that the form and
dimensions of this gas holder, and the materials of which it can be made
may be varied without any deviation from its essential properties as
they have been now described. For instance, the ends of the gas holder
may be formed of more than two folding plates, united together, if it is
judged necessary, and the levers F, G, may be varied in number, form, or
proportion, provided they balance the weight of the sides and cause the
lower edges of the gas holder to move nearly in an horizontal plane. Or
the balance levers may be laid aside entirely, and the gas holder may be
suspended from the upper part of the guide rods C, C, without moving up
and down thereon. But in this case it will require more water in the
tank to keep the open end of the gas holder always immersed in the
water; the weight of the sides of the gas holder will then tend more to
bring them together and to expel the gas.
In proportion as the quantity of water sufficient for the tank of the
collapsing gas holder is less than that required for the tanks of other
gas holders, it is attended with this further advantage, that the water
can be let off or removed without any expence when repairs are
necessary. If the repairs indeed are trivial, they can be made without
letting off the water at all, the depth being no more than one foot. In
the case, on the contrary, of the gas holder, with or without specific
gravity apparatus, the quantity of water is so considerable, that the
means provided for carrying it off must always be attended with great
difficulty and expence; and yet it is a provision which is in all cases
indispensable, no matter however difficult or expensive, for no material
repair to the interior of the apparatus can be otherwise effected.
With regard to the best size of a gas holder adapted to a certain number
of retorts, it may be stated, that this machine should be of a
sufficient capacity to hold the whole quantity of gas that is required
for the supply of the lights during one night, exclusive of what may be
furnished by the retorts during that time.
_Rule for finding the capacity of a Collapsing Gas Holder of given
dimensions._
The bulk of gas which a collapsing gas holder of given dimensions will
contain, may be found, by multiplying the area of the triangle contained
between the side plates when at their greatest extent, and the surface
of the water, by the mean length of the side plate. For example, suppose
the base of the triangular end plate be 30 feet long, and 30 feet high,
and that the length of the side plate at the top be 40 feet, and at the
bottom 60 feet,
30 × 15 = 450 area of end plate,
450 × 50 = mean length of end plate,
= 22,000 cubic feet capacity.[44]
[44] A collapsing gas holder of 22,000 cubic feet capacity, costs
about £. 800, it weighs eight tons; a collapsing gas holder containing
15,000 cubic feet, which weighs seven tons, costs about £. 700, and a
ditto containing 30,000 cubic feet costs about £. 1000. The depth of
the cistern for either is one foot.
_Reciprocating Safety Valve._
It must be sufficiently obvious that when the gas holder is full, and
the distillation of the gas continues going on, that unless a provision
is made for conveying away the surplus gas, it must escape by bubbling
up from underneath the gas holder. And should the gas holder happen to
be enclosed within walls, the gas may by chance accumulate, so as to
give rise to serious accidents.
As a remedy for this evil the manufacturers of coal gas have until very
lately contented themselves with what is called a _safety tube_, adapted
to the gas holder, by which, all the superfluous gas was carried away
into the open air; or by leaving large apertures in the roof or upper
part of the building, for the ready escape of the gas. By either of
these devices the danger from the accumulation of waste gas, was in part
only avoided, and instances might be named where dangerous consequences
ensued from an accumulation of gas, in a confined atmosphere, in the
vicinity of the upper part of the gas holder.
In some instances, indeed, recourse was had to the establishment of a
communication between all the reservoirs and an auxiliary gas holder or
gas holders, by means of a pipe furnished with an hydraulic valve; but
this was an expensive arrangement which required personal
superintendance, and depended, of course, for its efficiency on the
integrity and good conduct of the servant employed.
Mr. Clegg has now, however, invented what has been termed the
Reciprocating Safety Valve, which has a self-acting operation, and by
which an exit for the surplus gas of any number of gas holders that may
be in action is provided to an unlimited extent. A communication is
established between all the gas holders and a waste pipe, which
communication opens or closes by the action of the gas, as occasion
requires, and which may be extended to any number of gas holders at a
trifling cost.
The apparatus has now been adopted at the greater number of gas light
establishments, and has been uniformly found most efficient in its
operation. Fig. 9, plate VI., presents a perpendicular section of the
apparatus; _h_, _h_, _h_, _h_, is a small vessel made of sheet iron,
about eighteen inches in diameter, and twenty inches deep, closed at top
and open at bottom. It is inverted into an outer air tight vessel, _i_,
_i_, _i_, _i_, of double the height and rather greater diameter, which
is filled with water to a certain height; D, is a pipe communicating
with the gas holders that are in action; this pipe branches upwards
through the bottom of the outer vessel, _i_, _i_, _i_, _i_, and reaches
a little above the surface of the water in the outer vessel. E, is a
small pipe, the upper extremity of which is sealed by means of an
inverted sheet iron cup G, the edge of which is submersed under the
surface of the water in the outer vessel, _i_, _i_, _i_, _i_. This pipe
conveys the waste gas into the upper part of any chimney.
For let us suppose that the gas holders become overcharged; the gas must
then acquire an increased density before the wooden curb of the gas
holder G, fig. 7, plate VI.,[45] at the lower extremity of the
overcharged gas holder can begin to rise out of the water. But when the
elasticity of the gas is thus far increasing, and before the curb can
wholly emerge out of the water, the small vessel _h_, _h_, _h_, _h_, of
the reciprocating safety valve, ascends, and consequently establishes a
communication between the overcharged gas holder and the pipe D, of the
reciprocating safety valve. The surplus gas thus passes into the waste
pipe E, E, which had been before sealed by the inverted cup G, and is
hence conveyed into the upper part of the chimney where it terminates,
so that no accumulation of gas can ever take place above, or in the
vicinity of any gas holder.
[45] Every gas holder ought to have a wooden curb at the bottom.
It must be obvious on the other hand, that when the gas in any of the
gas holders has recovered its original density, the reciprocating safety
valve will again be closed by the descending of the cup G.