PART X.
Gas Metre, or Self-acting Guage, which measures and registers, in the absence of the observer, the quantity of Gas produced in a given time, from any given quantity of coal, or consumed during a given period, by any number of burners or lamps.
For the invention of this machine we are indebted to the ingenuity and talents of Mr. Clegg, and undoubtedly, of all the improvements with which the new art of procuring light has been recently enriched, there is none which has been attended with results more beneficial to the interest both of the manufacturer and consumer of coal gas.
In this machine we see combined a standard or check on the conduct of the workmen, which enables the manufacturer of coal gas to assure himself of obtaining at all times the greatest possible produce from his establishment; a measure by which he can deal the gas out to his customers in whatever quantities they may require it, and an index which registers the exact quantities furnished, and thus serves as an infallible account of debtor and creditor between the seller and purchaser of gas.
This machine, therefore, performs at once all the duties of an overseer, meter, and book-keeper, and performs them all so much more effectually, that its operation is not dependant on matters so uncertain as the care or integrity of servants, but on unerring principles which are fixed and incapable of any hidden misapplication.
The view in which this machine naturally demands our particular attention is that in which as a standard of the work which ought to be performed, it enables the manufacturer to make sure of obtaining the greatest possible produce from his establishment.
The gas metre serves this purpose in the first place by enabling the proprietors of gas works to know what is the utmost possible quantity of gas which can economically be obtained from any given portion of coal, with a given portion of fuel, in any given time.
It is necessary, in every gas light establishment, in order to know whether as much gas is obtained as might and ought to be produced, that it be previously ascertained by a series of experiments how much gas the species of coal used at the works is capable, on an average, of producing, and such data it is obvious, can only be obtained by means of an apparatus, which, like this gas metre, shall take measure of the quantities of gas supplied by the manufactory at all times, and under all circumstances.
It may, perhaps, be imagined, that assays sufficient for that purpose might be made by means of a few retorts, or small experimental apparatus, or by noting down the quantity of gas produced at the works during the time the valves which convey the gas into the street mains are shut, and during which time the capacity of the gas holders may afford a rule for ascertaining the quantity produced. But nothing can be further from the truth; assays of this description to be practically useful and to serve as a basis for the operations of a large establishment, must be made on a scale of magnitude and be continued for a considerable period of time as well as under every variety of circumstances.
The quantity of gas obtained from any given quantity of coal, varies so much with the degree of heat applied, and the circumstances under which the decomposition of the coal is effected, that the solitary product of any one period of time can afford no positive criterion for the product of any other period. A correct general conclusion, in short, can only be drawn from the result of experiments carried on uninterruptedly through a succession of days and nights, and such a continuity of experiments could, previous to the invention of the gas metre, only be affected by means of two separate gas holders, one for measuring the gas as it is produced, and the other for receiving the gas after it is thus measured, in order to its being transferred into the mains. By the aid of a single gas holder, an admeasurement could obviously be effected only during the time the valves which transmit the gas into the street mains are shut, and this, when the days are short, as in the winter season, the most productive period of the whole year, is only about eight hours out of the twenty-four, leaving nearly two-thirds of each day, during which, no account could be taken of the quantity of gas produced at the works.
It deserves further to be observed, that when two gas holders are employed, the utmost that can be effected by them, is the admeasurement of the gas produced, while the distinguishing feature of the metre is, that it not only measures, but by its own action registers the quantity of gas produced, or expended, in any given time.
Nor does the whole merit of this machine, in an economical point of view, consist in its thus furnishing the manufacturer with an infallible criterion of the quantity of gas which ought at all times to be produced; for, in the second place, it enables him by the several experiments which have supplied that criterion, to ascertain at what least possible expenditure of fuel, and in what space of time the greatest possible quantity of gas can be produced.
The advantage of the gas metre, in these additional respects, will be sufficiently demonstrated by attending for a moment to the situation of the manufacturer of coal gas, when without any such protecting register. Suppose, for example, that the manufacturer desires to know whether his workmen have made during a given time, (say during the night), the quantity of gas which they ought to have produced from a given quantity of coal, or whether they have consumed no greater proportion of fuel for its production than was absolutely necessary. He may, upon examination, find all the retorts in an excellent working state, but whether they have been so during the whole of the night, or whether the requisite quantity of gas has been really produced during the time that the valves which convey the gas into the mains have been open, is to him a matter of uncertainty. The workman may, as has been too often the case, have neglected the fire during the night, and on every such occasion, in order to bring back again the retorts to a proper working state, as well as to redeem the time lost, he may have urged the heat to a degree of intensity much exceeding the temperature best suited for the most economical production of the gas. And however injurious such irregular modes of operating may be for the master’s interest they are altogether shrouded from his observation. It deserves also to be noticed that the loss occasioned by this irregularity of operating is not merely a loss of fuel, for in consequence of it the retorts, (particularly if cast-iron retorts of the usual forms,) are liable to more injury in one day than they would be during a whole week, if properly attended.
When the proprietor of the establishment, on the contrary, has recourse to the gas metre, not one of all these evils can occur without being liable to certain and instant detection. From the data which preceding experiments on the productiveness of the species of coal used at the establishment have furnished, the overseer of the works is always enabled to determine, from the portion of coal he finds used, how much gas ought to have been manufactured during any space of time that has elapsed, and also the portion of carbonizing fuel which was necessary for the production of that quantity of gas; and comparing these data with the quantity of gas which the index of the gas metre announces has been produced, he is enabled to determine by mere inspection, in an unerring manner, whether the workman has acted with that sedulous attention to his duty which the economy of the establishment demands.
The many important advantages in short which the manufacturer of coal gas derives from this machine, considered as a standard or check on the conduct of the workmen, may be summed up in this—that while, without the aid of the gas metre, no establishment can be possibly more exposed to suffer from the ignorance of managers or the want of fidelity in servants, than a gas manufactory, there is none which is more independent of either than a gas manufactory, possessed of this important apparatus. Nor can the amount of that possible loss be regarded as otherwise than extremely serious, when attention is paid to the difference in profit and loss between conducting the process of manufacturing coal gas on a system founded on the deductions of experience, and an assiduous attention to keeping up a regularly sustained temperature; and conducting the process on a system of random calculation and irregular working,—a difference, which as appears from the details already laid before the reader, amounts in respect to the quantity of gas produced, to from fifty to one hundred per cent.; in respect to the waste of machinery, to upwards of eighty per cent.; and in respect to the consumption of fuel and time to a sum in the ratio of the loss experienced under both these other heads.
The Second General Point of View in which the gas metre claims our attention, is, its excellence as a standard of fair dealing between the seller and consumer of gas, by enabling the former to supply the gas in whatever quantities it may be required, and serving, at the same time, as a self-acting register of the quantities furnished. It is for this purpose merely necessary to connect the gas metre with the pipe of supply, which conveys the gas to any burner, or number of burners, or lamps, and the index of the instrument will regularly announce the precise quantity of gas which has passed through the machine during any period of time, from one day to a number of years, without requiring any particular sort of care whatever. Every person must have noticed how shamefully many individuals disregard the terms on which they have contracted for a supply of gas, some by means of the excessive flame they keep up, and others suffering the lights to burn hours beyond the time stipulated and contracted with the gas light company which supplies them. The latter have officers, it is true, whose duty it is to check such abuses as far as is in their power, but having no right of access to the premises of individuals, their vigilance can only extend to shops and places open to public view and of general access; and to these, of course, but occasionally. In short in every place where gas is supplied on contracts to pay for burning it a limited time, by means of certain sized burners or lamps, instead of according to the quantity actually furnished, the seller must always be in a greater or less degree, and in some cases wholly dependent on the care and honesty of the purchaser for the protection of his commodity from waste and depredation. But when on the contrary the seller possesses, as he now does, by means of the gas metre, an infallible check of the exact quantity of gas consumed in a certain time, and the purchaser is bound to pay for as much as he uses, the former is relieved from every apprehension or chance of being defrauded, and the latter is furnished with the same motives for economizing gas as he would have for economizing oil and candles.
The manufacturer is certain of obtaining what he has a just right to, value for the whole quantity of gas supplied, and the consumer is assured that if he wastes the gas unnecessarily, he must as he ought, pay the price of his own carelessness or profusion. Equal justice is done both to the consumer and seller, and the public at large are at the same time most materially benefited, in as much as they are saved from paying for the expence of that waste of gas by a few, which from the former impossibility of tracing it to the offending parties, was necessarily added to the whole cost of the gas, and equally partitioned upon all the individuals who made use of it. The waste being now transferred to those who occasioning the waste and ought alone in justice to bear it, the price of the gas to the equitable and honest consumer, is thus reduced to an equitable and correct measure of value.
The benefits of this invention have a yet wider range; not only does it secure full value for the whole of the gas manufactured, but it tends to make the gas a greatly more marketable article. For in the system of charging for the supply of gas by the year, half year, or quarter, and at one common rate, many individuals who are only occasionally in want of gas lights, or whose demand is irregular and uncertain, such as the proprietors of public rooms, theatres, &c. are debarred of availing themselves of this kind of illumination, except at an expence quite disproportioned to what other more regular customers pay, and out of all proportion of the value of the quantity of gas consumed by them. The gas light under such circumstances is not as it ought to be, a light for all. It is not as oil and candle are, a benefit which every one may obtain who is in need of it, and in such quantities as may best suit his means and convenience. One of the capital advantages, of the gas metre, however, is, that it makes gas a substitute for oil and candles, applicable under all circumstances, and that it enables the manufacturer without the least prejudice or chance of prejudice to his interest, to supply gas in whatever quantities it may be demanded, and at a fair proportioned price.
In speaking thus of the influence which the gas metre must have in attending the beneficial application of the new lights, we are not unaware that situations may present itself where the action of the metre might be impeded from the want of a sufficient pressure of the gas in the pipe of supply connected with it. But this can never be the case except where the pressure of the gas in the pipe of supply is so low as three-eighths of an inch of a column of water, and in all such cases it is only necessary to give a greater capacity to the wheel of the machine, than would be necessary under other circumstances, and this will at once make up for the inferiority of pressure. In point of fact, therefore, no situation can occur, where the application of the machine may not be rendered available.[46]
[46] See directions to workmen, for adapting gas metres, [p. 229].
Nor do the various advantages which have now been detailed, form all the good that this important machine is capable of furnishing. The gas metre furnishes at its axis a power which has been ingeniously applied to put in motion the shaft of the lime machine, employed for purifying the gas, see fig. 3, [plate VII.][47] The importance of a power thus certain in its operation, and obtained free of expence, must at once be obvious, when it is considered that upon whatever plan the purifying apparatus or lime machine may be constructed, it is absolutely essential, that its contents be kept constantly in motion, in order to produce the desired effect upon the crude gas, which would otherwise pass away in an impure state.
[47] The upper axis communicates with the agitating shaft of the lime machine, and the lower axis is a continuation of the shaft of the gas metre. The two pullies are connected by a strap.
When the charge of keeping the agitating shaft of the lime machine in action, is intrusted to a workman, there is no positive security against his occasionally neglecting his duty, whereas by applying the gas metre to that purpose, the manufacturer is assured beyond the possibility of deception, that when gas is produced, that gas is as certainly purified, and a saving is effected in point of labour of the expence of two men, one during the day, and one during the night.
Description of the Gas Metre at the Royal Mint Gas Works.
Fig. 4, [plate II.], represents a perpendicular section of the gas metre. It is placed between the purifying apparatus or lime machine, and the gas holder fig. 8, [plate III.], exhibits a front elevation; fig. 1, [plate III.], a perspective view, and fig. 6, [plate III.], a transverse section of the machine.
It consists of a hollow wheel or cylinder, made of thin iron plate, revolving upon an horizontal axis, in the manner of a grindstone; this wheel is enclosed in a cast iron air tight case containing water.
The cylinder or wheel, is composed of two circular channels, 1 and 2, fig. 4, [plate II.], concentric to each other. The larger or outer channel 1, is divided into three equal compartments, by partition plates, marked a, as shewn in the design. The compartments are provided with hydraulic ducts or valves, made at the upper part of every partition plate a, a, a, and by means of them a communication is formed between the larger concentric channel 1, and the outer case in which the wheel revolves.
Similar valves are also placed at the foot of each partition plate, they are seen near the letters a, a, a, and by this means, a communication is established, between each compartment or chamber of the larger concentric channel 1, and the smaller interior circle 2, of the wheel.
On inspecting the design, it will be seen that the valves are situated in opposite directions to each other, hence there can be no communication either between the inner smaller concentric channel 2, and the larger compartment of the wheel 1, nor between the latter compartment, and the exterior case, in which the wheel revolves, except, through the valves a, a, a, which form the communicating ducts. It will be seen also, that these valves are carried from one chamber of the machine into another, but in opposite directions; the entry into one chamber, being in the opposite direction to the hydraulic duct, placed in the other chamber.
From these particulars the action of the machine will be obvious.
Let us suppose that the outer case (which is marked in the sketch by a black tint,) in which the wheel revolves, be filled with water, to about an inch above the axis of the wheel, and that gas is conveyed into the interior small channel, by a pipe, passing along the axis, so as to allow the wheel to turn freely round, and that the pipe is turned up at right angles in the inner chamber, and projects a little way above the surface of the water, as shewn in the design. The gas then must enter into the interior chamber of the wheel above the surface of the water, and must press against the adjacent partition; it will therefore cause the wheel to turn round, and in consequence of this motion, the next partition plate will press the gas against the surface of the water, and cause it to pass through the hydraulic opening, in an equal quantity to that, which is introduced into the exterior chamber.
This alternate filling, and discharging, of the contents of each chamber, will take place once during every revolution of the wheel, and hence the number of times each particular chamber has been filled, and emptied of gas, may be known.
In fact this machine performs the office of three revolving gas holders, fixed on an horizontal axis, and moving in a cistern, which is the outer case of the machine. One gas holder, or one compartment of the machine, is always in the act of becoming filled with gas, another is emptying its contents into the outer case, from which it passes into the reservoir, where it is to be stored up, or to the lamps, where it is to be burned, and the third compartment is stationary, or in an equilibrium. The wheel in any situation will therefore always have one of its receiving, and one of its discharging valves open, and consequently it will revolve.
Now to ascertain the quantity of gas discharged by one revolution of the wheel, we need only to know the capacity of the chambers, and add them together. Let us for example suppose, that each chamber contains 576 cubic inches, then one revolution of the wheel, discharges a cubic foot of gas. To register the total number of revolutions which the wheel makes in a certain time, a train of wheel-work is connected with the axis of the metre, see fig. 8, [plate III.]; it consists of a pinion impelling a common train of wheel-work, composed of any number of wheels. The pinion on the axis of one wheel, acts into the circumference of the next wheel, and the circumference of the wheel being as ten to one, it is obvious whilst the metre makes 100,000 revolutions, if the series consists of six wheels, the last wheel of the series, will only have made one revolution. Each axis of the wheels is provided with a finger and dial plate, divided into ten parts, therefore any number of revolutions may be read off at any time by inspection betwixt 10,000,000 and one.
The velocity with which the metre acts, is of course in proportion to the quantity of gas passing through it. Thus suppose there is a burner or gas lamp connected with the machine, of one foot capacity lighted, which consumes four cubic feet of gas in an hour, the gas metre performs four revolutions per hour, and so on for every number of burners or lamps, not exceeding the number which the machine is calculated to supply.
To render the construction of the gas metre more obvious, we have at fig. 6, [plate III.], exhibited a transverse section of the machine; a, is the outer case of the machine in which the wheel revolves. B, B, the outer or larger concentric chamber, (marked 1, in fig. 4, [plate II.]) L, the inner or smaller concentric chamber, (marked 2, in fig. 4, [plate II.]) d, the index on the axis which passes through a stuffing box in front of the machine. 5, 5, 5, 5, are stays or braces for supporting the wheel; they are likewise seen in fig. 4, [plate II.] A, is the inlet pipe for the gas to enter into the machine. The gas passes through the pipe h, and from thence into the curved pipe i, into the interior chamber L, of the metre. The pipe h, is surrounded by a second pipe K, which has a small aperture at x, the office of which is, to act as a siphon, in order to preserve the proper level of the water in the machine. The water is poured into the machine, through the small funnel at the back of the entrance pipe A. y, is a float, which stops the performance of the metre altogether, if a fraudulent attempt should be made, to stop the registering of the metre, by drawing off the water with which it is charged. In fig. 1, [plate III.], a, is the inlet pipe; b, the outlet pipe of the gas; and fig. 2, shows the interior chamber.
The registering wheel work, may be adapted to any part of the machine, and the motion may be communicated by a mitre wheel, from the shaft of the machine to the index.
The gas metre at the Royal Mint measures and registers 30,000 cubic feet of gas every twenty-four hours.[48]
[48] The gas metre at the Bristol gas works registers 60,000 cubic feet of gas every twenty-four hours. The metre at the Chester gas works registers 40,000 cubic feet every twenty-four hours.—One of the metres at the Birmingham gas works registers 40,000 cubic feet, and the other (now erecting) will register 100,000 cubic feet every twenty-four hours.
Rule for calculating the weight, which a Gas Metre of given dimensions, will raise to a given height, in a given time.
The following calculation will exemplify the power produced by a gas metre constructed to register 60,000 cubic feet of gas, in a day. The diameter of such a metre would be six feet, its depth three feet, and the depth of its rim eighteen inches.
The section of the rim would therefore contain 648 square inches, and supposing the pressure of the gas passing into the machine to be equal to a column of water two inches high, its buoyant power would then be equal to 1296 cubic inches of water, or forty pounds and a half weight. The mean diameter of the metre is 4 feet 6 inches, which multiplied by three, gives the perpendicular height that forty pounds and a half weight, would be raised by each revolution of the metre. The number of revolutions, in one hour which the metre makes, is 40, they would raise forty pounds and a half, 540 feet high in one hour.
Such a power is more therefore than sufficient to keep in motion the shaft of the lime machine.
Gas Holder Valve,—Siphon, or Water Reservoir.
This name is given to the principal hydraulic valve, by means of which a communication is established between the gas holder or gas holders, and the principal pipe, leading to the mains.
Fig. 7, [plate III.], exhibits a section of this valve. It is composed of an air tight box, A, A, A, A, containing a portion of tar, or water; d, is the inlet pipe which communicates with the gas holder, B the outlet pipe; which conveys the gas into the mains. C, C, is an inverted cup, furnished with a sliding rod, passing through a stuffing box, so that by means of the rod, the cup may be raised or depressed. For it is obvious that a communication will be established between the inlet pipe d, and the outlet B, when the cup is raised above the surface of the tar or water in the box A; and that the communication will be cut off when the cup is depressed into the tar. In the latter position the cup is shewn in the design. The sliding rod which raises and depresses the cup, passes through a frame E, E, affixed to the upper part of the box A, and which serves as a guard for the rod, so that it may be locked by means of a cutter passing through the sliding rod, and the frame of the box.
Fig. 3, [plate III.], exhibits a similar valve, which at the same time may be used as a water reservoir, commonly called a siphon, for collecting the water that may happen to accumulate in the mains, a provision which it is essential should be made at the lowest place, where two or more pipes incline towards each other. For it is obvious, that if a fluid should happen to accumulate in the angular part, where two descending pipes meet, to a height sufficient to fill the angular point, the communication between the two pipes would be completely cut off, so that the gas could not pass. x, x, x, x, fig. 3, is the reservoir; A, the inlet pipe; B, the outlet pipe; b, a short cylinder communicating with the exit pipe B, it is open at bottom and closed at top. D, d, the hydraulic cup which, when raised by means of the spindle e, closes the exit pipe B, by the open end of the cylinder b, becoming immersed in the tar or water contained in the cup D, d. The darts show the course of the gas when the valve is open: f is a small pipe furnished at top with a screw and covered with a cap; by attaching a hand pump to this pipe, the superfluous portion of fluid that may have accumulated in the reservoir, may be removed. c, c, is the equilibrium pipe, it connects the exit pipe B with the inlet pipe A, when the stop-cock with which it is furnished is opened. This pipe prevents the tar or water from being blown out of the hydraulic valves that may be interposed between the different descending mains of a district, as would otherwise happen, in consequence of the sudden concussion that takes place when the main or gas holder valves are opened. Because the gas in the mains, and the gas in the gas holders, are not in equilibrium. But by means of the small pipe c, c, the equilibrium is obtained when the stop-cock of the pipe c, c, is opened, and this should always be done before the main or gas holder valves are opened. For by neglecting this condition, the water or tar is liable to be blown out of all the hydraulic valves, that may happen to be interposed in the system of the pipes for conveying the gas, and communications are thus opened, which were intended to be shut.