Life of Richard Trevithick by F. Trevithick: Volume 1: Chapter 5
CHAPTER V. PLUNGER-POLE PUMP AND WATER-PRESSURE ENGINE.
An account-book, in Trevithick's writing, commences:-
1797. To Ding Dong, for five weeks' attendance, at a guinea a week.
Ditto, fixing a 7-inch pole-case with new lifts and wood wind-bore.
1798. Fixing, in East Pool Mine, a 4.5-inch pole, &c.
Ditto, the same in Prince William Henry.
These and similar entries are frequent in what appears to have been commenced as Trevithick's ledger-account of outgoings and incomings on his taking the post of chief mine engineer, made vacant by the death of his father. Men's wages are charged at numerous mines for putting in pit-work, building engine-houses and boiler-houses and various entries for wood, leather, pumps, &c., for pit-work.
The increasing depths of the mines, and greater power of the steam-engines for raising water, necessitated a change in the rude, weak pit-work, with pumps made of wood hooped with iron, having buckets with leather-cup packing and valve which only raised water with the upward motion of the rods. Pistons without valves, similar to those used in steam-engines, worked in brass or iron pump-barrels, forcing the water upward with the downward movement of the pump-rods, reducing the strength and weight of the pump bucket-rods by one-half. Their descending weight about balanced the ascending water, while with the valve-bucket pump the rods had to be strong enough to bear their own weight and also that of the column of water.
The practical cause of failure of the solid piston was its liability to jam in the pump-barrel by sand or gravel; while the breakage of a leather-cup bucket, or leakage of its leather valve, was apt to cause serious accident to the costly pump-rods, and even to the steam-engine.
The plunger-pole made useful in the Cornish mines by Trevithick, met all the requirements; raising the water by the descending pump-rods, having great simplicity of structure, and freedom from breakage or liability of jamming.
The great value of this invention or application is proved by its continued use in pump-work, precisely as erected by Trevithick in 1797. Plunger-poles, fitted to the case, the latter having longitudinal grooves for the passage of the water, had been used in France; but Trevithick's plunger-pole worked in an unbored pole-case the sides of which were not touched by the pole. The upcast pipe shown close to the top of the pole-case allowed the free escape of air it is now, however, more frequently attached to the bottom of the pole-case. By leaving the packing in the stuffing box a little slack, air escapes; while a water cup on the top of the stuffing-box gland prevents the admission of air through the slack packing.
With the old atmospheric engine common buckets pumps were employed, the whole depth of the shaft being divided into several lifts; and the rods of each pump, ascending separately to some distance above the topmost lift, were then united to one rod attached by a chain to the engine-beam.
When Watt's engine was introduced, the pit-work remained pretty nearly the same, except that, instead of the long separate rods to each lift, one main rod was substituted, to which smaller rods were attached by ties, to work the pumps at the various levels where they were required. This arrangement has continued to the present day, and is much superior to the old plan.
Among other things, Murdoch proposed the use of Sir Samuel Morland's plunger-pump in the pit-work, not as a general substitute for, but as an addition to, the lifting pumps, in. order to suit the double-acting engine, by making the pumps double-acting also. In 1796, one of those was employed at Ale and Cakes, a mine now forming the eastern part of the United Mines.
Murdoch apparently used, in Ale and Cakes Mine, a plunger-pole to suit the particular requirements of Watt's double-acting engine. Trevithick's account, commencing in the following year, deals with plunger-pole pit-work, not as a makeshift, but as a principle on which pit-work in a mine should be constructed. He removed the old lifting-bucket pit-work and replaced it by the plunger pit-work in several mines, in 1797.
Probably neither Murdoch nor Trevithick knew of its having been patented one hundred years before, which takes from them the claim of invention, though the practically useful introduction rests with Trevithick.
Gregory's Mechanics,' a much-esteemed book on pump-work, speaks highly of Trevithick's temporary forcer, and gives a drawing of it.
Forcer, temporary, for a pump, is a contrivance to produce a constant stream. A very simple forcer of this kind has been devised by Mr. R. Trevithick it consists in fixing a barrel with a solid piston along the side of the common pump, in such a manner that the lower space of the additional barrel may communicate with the space between the two valves of the pump, and lastly, by connecting the rods so that they may work together. The effect is, that when the pistons are raised the spaces beneath A and B become filled by the pressure of the atmosphere, at the same time that the upper column flows out at E. But again, when the pistons descend the valve C shuts, and consequently the water driven by the piston in B must ascend through A, and continue to produce an equal discharge through E in the down-stroke.
This combined bucket and forcer pump, known under the name "Trevithick's pump," gives him the claim of invention. His account-book, commencing in 1797, does not warrant the supposition that his plunger-pole pit-work was only then used for the first time.
The diffusion of useful knowledge was in those days so remarkably slow, that the managers of neighbouring mines went each his own particular course, in ignorance of changes and improvements that others were benefiting by. Lean tells us that,
In 1801, in Crenver and Oatfields, in the parish of Crowan, be found the pit-work to consist of leathern buckets, with two or three pistons, such as were at that time in general use for plungers, in a very bad state; and it may be safely asserted that the engines were idle at least one-third of the time, repairing the pit-work and changing the buckets. And here lie first introduced (what is now so generally used, and with so great advantage) the plunger-pole, instead of the common box and piston, wherever he found it practicable.
It is evident that the plunger-pole, before Trevithick took it in hand, was a floating idea struggling to become a reality. Its great value is in its simplicity, amounting to a principle, not generally known to the miners in Cornwall in 1801, as the pump to supersede all others, in deep mines.
Trevithick's first move was to meet the requirements sought for by Murdoch — the lifting of water by the down-stroke of the pump-rods as well as by the up- stroke, exemplified in the temporary forcer, in which the pump-bucket, with its valve, and the solid piston, were placed side by side, one common bottom-valve serving for both pumps. The result of the combination was a constant upward stream of water and the non- necessity for the top valve in the water column the water from the force-pump barrel passed up through the bucket-valve in the pump-barrel on the down- stroke, while the up-stroke propelled the water from the pump-barrel. Gregory calls it the "Trevithick forcer, temporary," as though it was soon to be replaced by the still more simple plunger-pole.
The pole-case was a plain casting with a box for the hemp packing the pole was a cast-iron pipe turned on the outside, and fixed like a ferrule on the end of the pump-rods. Two valves formed of two plates of iron, with a piece of leather between them, the lower plate being less in size than the upper, caused the leather to form the face of the valve, making it water-tight without employing skilled labour in its construction.
The perfect simplicity of each small part, built on ideas partly new and partly seen or heard of before, but scarcely traceable, constituted the invention.
Mrs. Dennis recollected Mr. Trevithick at Ding Dong about 1797 fixing his new plan of pumps there, and at Wheal Malkin and Wheal Providence, adjoining mines. Her parents lived at Madron, near these mines, and for two or three years Mr. Trevithick came frequently to superintend the mine-work, staying at their house a few days, or a week at a time. He was a great favourite, full of fun and good-humour, and a good story-teller. She had to be up at four in the morning to get Mr. Trevithick's breakfast ready, and he never came to the house again until dark. In the middle of the day a person came from the mines to fetch his dinner; be was never particular what it was. Sometimes, when we were all sitting together talking, he would jump up, and before anyone had time to say a word, he was right away to the mine.
Henry Clark went to work in Dolcoath smiths' shop in 1799. Captain Trevithick was putting in a plunger-pole lift; everybody said it would never answer, but the same lift is working there to this day (1869). Before that time they used buckets and pistons packed with gasket and a ring screwed on it; they used to jam with sand and gravel.
Trevithick followed up the application of his new plunger-pump with such energy, that during the succeeding four or five years several of the principal mines had removed their old bucket-lifts, to make room for the new Munger pole lift, and among them Dolcoath Mine.
In 1798 Trevithick, by one of those moves common to master-minds, converted the outline of the plunger-pole pump, serving as the agent of the steam-engine, into its rival as the prime mover in positions commanding a stream of water through pipes from elevated ground. In this new position it was called the water- pressure engine, and its first erection was in Prince William Henry Mine, for giving motion to the pump-rods. The pole and case took the place of the cylinder and piston of the steam-engine, and were fixed over the mouth of the shaft. The pole working through a stuffing box on the top of the pole-case, had a cross-head, from which two side rods descended to the pump-rods; water was brought in iron or wood pipes from the neighbouring high ground, and being admitted by a valve to the bottom of the pole, caused it to perform the up-stroke the release of the water from under the pole allowed the weight of the rods to cause the down-stroke. This first Cornish water-pressure engine continued to work satisfactorily for seventeen years, when it required repairs, and was re-erected.
Captain Joseph Vivian, the manager of Roskear Mine in 1868, also worked there in 1815, when they re-erected the old water-pressure engine that Trevithick had first put up in 1798. It was spoken of as the first water-pressure engine ever erected with a pole and side rods. The water was brought through pipes for working it.
Mr. Symons, when a boy, in 1804 or 1805, used to amuse himself by placing a handkerchief on a plug in the wooden water-pipes with iron bands, bringing water down from Carnkie to work Captain Trevithick's water-pressure engine at Wheal Druid. By loosening the plug, it flew from the pipe up into the air, carrying the handkerchief up with it, to the great fun of the boys; only sometimes, when the engineman could surprise them, they had the rope's end.
A very complete pressure-engine was erected by Mr. Trevithick at the Druid copper mine in Illogan, near Truro, in Cornwall it acted with a double power, that is, the piston pressure was first applied to one side of the piston to force it up, and then on the other to force it down, in the same manner as a double-acting steam-engine. It acted by two slide-valves instead of one, but they were so made that one opened rather before the other shut, and this, though it wasted a small quantity of water by permitting it to escape, prevented the concussion of stopping the column of water, which indeed is always in motion.
Mr. James Banfield in 1818 was employed in Wheal Clowance Mine the pumps were worked by Captain Trevithick's wafer-pressure engine. It had a pole about twelve inches in diameter, working in a pole-case; two side rods went down from the cross-head on the top of the pole, to a cross-head under the pole-case; to this bottom cross-bead the pump-rods were joined the cross-heads worked in wooden guides; there was a balance-bob from which a plug-rod worked the valves, which had gear-handles just like a steam-engine. The engine was fixed underground at the adit level the head of water came from Clowance Park. Several similar engines were then at work in the Cornish mines they used to be called Captain Dick's pressure-engines.
The temporary forcer pump was a combination of pump-bucket and solid forcer piston. Before it had time to be practically established in general use, it was followed by the plunger-pole pump. Then came the pole pressure-engine, for giving motion to the plunger-pole pumps, followed by the Druid Mine double-acting pressure-engine, with solid piston, and water pressure acting both on its up and down stroke like the Watt steam-engine, but using water pressure and vacuum in lieu of steam and vacuum.
The pressure-engine described by Rees was double-acting, having a piston in a cylinder; that by Banfield was single-acting, with a pole, of which several were at work in Cornwall in 1815, and were known as Captain Trevithick's pressure-pole engines.
Gregory's Mechanics, published in 1806, gives a drawing and full particulars of Trevithick's Wheal Druid pressure-engine.
Pressure-engines for raising water by the pressure and descent of a column enclosed in a pipe, have been lately erected in different parts of this country. The principle now adverted to was adopted in some machinery executed in France about 1731 (see Belidor de Arch., Hydraul., lib, iv., ch, i.), and was likewise adopted in Cornwall about forty years ago. But the pressure-engine of which we are about to give a particular description, is the invention of Mr. R. Trevithick, who probably was not aware that anything at all similar had been attempted before. This engine, a section of which, on a scale of a quarter of an inch to a foot, is shown in Pl. xxiii., was erected about six years ago at the Druid copper mine, in the parish of Illogan, near Truro. A B represents a pipe 6 inches in diameter, through which water descends, from the head, to the place of its delivery, to run off by an adit at S, through a fall of 34 fathoms in the whole that is to say, in a close pipe down the slope of a bill 200 fathoms long, with 26 fathoms fall; then perpendicularly 6 fathoms, till it arrives at B, and thence through the engine from B to S 2 fathoms. At the turn B the water enters into a chamber C, the lower part of which terminates in two brass cylinders 4 inches in diameter, in which two plugs or pistons of lead, D and E, are capable of moving up and down by their piston rods, which pass through a close packing above, and are attached to the extremities of a chain leading over, and properly attached to the wheel Q, so that it cannot slip. The leaden pieces D and E are cast in their places, and have no packing whatever. They move very easily, and if at any time they should become loose, they may be spread out by a few blows with a proper instrument, without taking them out of their places. On the sides of the two brass cylinders, in which D and E move, there are square holes, communicating towards F and G, which is a horizontal trunk or square pipe, 4 inches wide and 3 inches deep. All the other pipes, G, G, and R, are 6 inches in diameter, except the principal cylinder, wherein the piston H moves; and this cylinder is 10 inches in diameter, and admits a 9-feet stroke, though it is here delineated as if the stroke were only 3 feet. The piston-rod works through a stuffing box above, and is attached to M N, which is the pit-rod, or a perpendicular piece divided into two, so as to allow its alternate motion up and down, and leave a space between, without touching the fixed apparatus or great cylinder. The pit-rod is prolonged down into the mine, where it is employed to work the pumps, or if the engine were applied to mill-work, or any other use this rod would form the communication of the first mover. K L is a tumbler, or tumbling bob, capable of being moved on the gudgeons V from its present position to another, in which the weight L shall bang over with the same inclination on the opposite side of the perpendicular, and consequently the end K will then be as much elevated as it is now depressed. The pipe R S has its lower end immersed in a cistern, by which means it delivers its water, without the possibility of the external air introducing itself, so that it constitutes a Torricellian column, or water barometer, and renders the whole column from A to S effectual, as we shall see in our view of the operation.
Let us suppose the lower bar K V of the tumbler to be horizontal, and the rod P 0 so situated as that the plugs or leaden pistons D and E shall lie opposite to each other, and stop the water-ways G and F; in this state of the engine, though each of these pistons is pressed by a force equivalent to more than 1000 lbs., they will remain motionless, because these actions being contrary to each other, they are constantly in equilibrio. The great piston H being here shown as at the bottom of its cylinder, the tumbler is to be thrown by hand into the position. here delineated.
Its action upon 0 P, and consequently upon the wheel Q, draws up the plug D, and depresses E, so that the water-way G becomes open from A B, and that of F to the pipe R; the water consequently descends from A to C, thence to G G G, until it acts beneath the piston H. This pressure raises the piston, and if there be any water above the piston, it causes it to rise, and pass through F into B. During the rise of the piston (which carries the pit-rod M N along with it), a sliding block of wood I, fixed to this rod, is brought into contact with the tail K of the tumbler, and raises it to the horizontal position, beyond which it oversets by the acquired motion of the weight L. The mere rise of the piston, if there were no additional motion in the tumbler, would only bring the two plugs D and E to the position of rest, namely, to close G and F, and then the engine would stop; but the fall of the tumbler carries the plug D downwards, quite clear of the hole F, and the other plug E upwards, quite clear of the hole G. These motions require no consumption of power, because the plugs are in equilibrio, as was just observed. In this new situation the column A B no longer communicates with G, but acts through F upon the upper part of the piston H and depresses it; while the contents of the great cylinder beneath that piston are driven out through G G G, and pass through the opening at E into R.
It may be observed that the column which acts against the piston is assisted by the pressure of the atmosphere, rendered active by the column of water hanging in R, to which that assisting pressure is equivalent, as has already been noticed. When the piston has descended through a certain length, the slide or block at T, upon the pit-rod, applies against the tail K of the tumbler, which it depresses and again oversets; producing once more the position of the plugs D E, here delineated, and the consequent ascent or the great piston H, as before described. The ascent produces its former effect on the tumbler and plugs; and in this manner it is evident that the alternations will go on without limit, or until the manager shall think fit to place the tumbler and plugs D E in the position of rest, namely, so as to stop the passages F and G.
The length of the stroke may be varied by altering the position of the pieces T and I, which will shorten the stroke the nearer they are together, as in that case they will sooner alternate upon the tail K.
As the sudden stoppage of the descent of the column A B at the instant when the two plugs were both in the water-way might jar and shake the apparatus, these plugs are made half an inch shorter than the depth of the side holes, so that in that case the water can escape directly through both the small cylinders to H. This gives a moment of time for the generation of the contrary motion in the piston and the water in G G G-, and greatly deadens the concussion which might else be produced.
Some former attempts to make pressure-engines upon the principle of the steam-engine have failed, because the water, not being elastic, could not be made to carry the piston onwards a little, so as completely to shut one set of valves and open another.
In the present judicious construction the tumbler performs the office of the expansive force of steam at the end of the stroke.
The head of water at Wheal Druid had a fall of 204 feet. The design of the valve-box alone showed genius sufficient to place a man above his fellows. Two cylinders of brass, easily fitted up, two leaden piston-valves, cast in their places, without any fittings, which in case of wear could be hammered out to the necessary size without taking them from their places. These two valves were moved by a piece of flat chain passing over a pulley, attached to a wooden lever, with a balance-weight judiciously placed, called a tumbling bob.
The operation of these simple valves was that each of them bearing a pressure of more than 1,000 lbs., worked as balance-valves with little weight or friction, or wear and tear, and enabled the engine to change its direction of stroke without jar, and without materially stopping the downward flow of water in the supply- pipe. The plugs, since called by modern inventors cylindrical slide-valves, being made half an inch shorter than the water passages in the brass cylinder, or valve- case, turned the water pressure from the main cylinder into the waste-pipe during the moment of time occupied in changing the direction of the stroke. This one little point in the engine was thus valued by Gregory:-
Some former attempts to make pressure-engines upon the principle of the steam-engine have failed, because the water, not being elastic, could not be made to carry the piston onwards a little, so as completely to shut one set of valves and open another. In the present judicious construction the tumbler performs the office of the expansive force of steam at the end of the stroke." The bottom end of the waste-water pipe emptied into a cistern 12 feet below the engine, to prevent air from going up the pipe. The weight of water, therefore, in this pipe gave a vacuum in the working cylinder of several pounds to the inch. This apparently small engine was of great power, the pres. sure being about 100 lbs. to the inch on the piston, giving a force of three or four tons, thrown rapidly lip and down the long stroke of 9 feet.
Trevithick was for several years the engineer and part proprietor in Trenethick Wood Mine, and introduced his improved plunger-pole pumps, worked by his piston water-pressure engine. The cylinder was 17 inches in diameter, with a stroke of 9 feet, double-acting, worked by a four-way cock, made of brass, in a brass shell. An air-vessel was suggested to remove the shock of the change of movement in the column of water. The head of water was 78 feet, giving a power of nearly four tons.
The drawing of this engine, still in the possession of the Honourable Mrs. Gilbert, of Trelissick, was made by Trevithick, and given to his friend Davies Gilbert (then Giddy), who wrote the following particulars on it:—
Drawing of the pressure-engine, erected on the mine in Trenethick Wood, near Helston, 1799. Given me by the engineer, Mr. Richard Trevithick. The fall of water is 13 fathoms; the engine works double; a 9-feet stroke. The parts are,—a tube communicating with the head of water the cylinder or working piece; a tube communicating at the bottom with the cylinder and a tube acting as a siphon, and thus adding the length of the cylinder to the head of water. When the cock is turned, as here represented, the water from the tube presses on the piston in the cylinder. The water under the piston is forced up the tube, and flows down the siphon. When the cock is turned a quarter round, the water from the tube ispressed down the tube; from thence acts against the under surface of the piston in the cylinder. The water above the piston escapes into the siphon.
N.B.— An air-vessel may be adapted to the tube, and thus the flow of water rendered almost uniform, checks of the engine. The apertures nozzles are made one quarter of the cylinder.
The balance-valves are here replaced by the four-way cock. The simplicity of form and parts leads one to pass by this machine as merely a few pipes bolted together; but its great power and economy in working led to its use in other than Cornish mines.
At a meeting of the Hill-Carr Sough proprietors, held June 25th, 1801, it having been represented to the meeting that pressure-engines of the description proposed to be erected near Youlgreave, are now in use in Cornwall, where they give great satisfaction, and Mr. Richard Trevithick, the engineer who erects them, having made an offer to come to view the mines paying composition to this Sough, on condition of the expenses of his journey being paid; and that in case of not contracting for the erection of the engine, he would furnish us with drawings and every information gratis.
March 25th, 1802. At a meeting this day, the adjourned question respecting the propriety of erecting an engine to lift the water below the level of this Sough was further considered; Mr. Richard Trevithick having given in a drawing and an estimate of an engine for a lift of 8 fathoms.
The undersigned proprietors agree to accept the above proposals on condition that the whole of the expenses shall not exceed £1,800.
In the reckonings for the quarter ending 27th March, 1802, the Hill-Carr Sough and the Shining Sough partners each pay £15, as half of the expenses of Mr. Trevithick in making a plan for an engine, and for coming over out of Cornwall with it; together £30.
At a meeting held March 31st, 1803, Mr. Richard Trevithick having appeared, and produced estimates of the pressure-engine, and also of a wheel calculated to lift the whole of the water in the Black Shale Pit and Gay Vein Gates to the depth of 8 fathoms, from which it appeared that the expense of the pressure-engine was less, and also came recommended by Mr. Trevithick in preference to the wheel; it was unanimously ordered that the former should be adopted, and the whole and entire management of it be entrusted to Mr. Trevithick, pursuant to the conditions which he required.
At a meeting, June 28th, 1804, allusion is made to the engine then being erected. Half a century had passed since these resolutions of the managers of the Derbyshire lead mines to entrust a Cornish engineer with their drainage, when the following notice was attached to this memorable old water-pressure engine, — " November, 1851, Messrs. John Taylor and Sons advertise for sale the various engines and pumps in those old mines;" and in 1852 they were drawn up and sold, Trevithick's engine going to the scrap-pile after fifty working years.
ALPORT, near BAKEWELL,
March 8th, 1869.
I am glad to learn by your favour of the 4th that the particulars I sent of the pressure-engine will be of service, and that, with some help from Mr. Darlington, you will be enabled to make a drawing of it. There is one thing I believe I have not named, it is that this engine has many times worked for fifteen or sixteen weeks together, without missing a stroke or being stopped for any purpose (a moment once or twice a day, do not recollect which) but to oil the bearings. The water was very clear and did not wear the valves and gearing of the buckets very much.
F. TREVITHICK, Esq
MINERA, near WREXHAM,
1st March, 1869.
The sketch you have sent me of Trevithick's engine perfectly correct, and I can only answer the questions asked in your letter.
The pump-work at the Alport mines were two 33-inch drawing lifts, connected above the cylinder to the piston-rod by a cross-head; the bottom of the cylinder was at the adit level. The tumbling beam for working the boxes or valves was fixed about 12 feet above the revolving wheel, with a small rod connected to a short lever fixed to the axle of the revolving wheel. The tumbling beam was worked by two tappets, screwed on the rod that was connected with a powerful balance-beam on the surface. This rod was also connected with the cross-head below, stayed, or worked through guides, as the ordinary Cornish pit-work.
The water for working this engine descended to the piston below, from the surface, through a 15-inch downfall column, about 150 feet in depth. The regulating valve to this engine was on the surface, and the water was turned on according to the necessary speed of engine. I hope you will see how to form your sketch of this engine from what is stated above. If there is any other question you wish to ask, I will endeavour to answer it.
Yours very truly,
F. TREVITHICK, Esq.
Mr. J. Glynn, in a report on water-pressure engines, says:—
The first water-pressure engine used in England was erected by Mr. William Westgarth, at a lead mine belonging Sir Walter Blacket, in the county of Northumberland, in the year 1765. The piston was attached by a chain to the arched head of the beam, working just like the atmospheric steam-engines Mr. Smeaton suggested to Westgarth the use of a stuffed collar, which he used with success. In 1770 Mr. Smeaton made a small water-pressure engine for supplying Lord Irwin's residence, closing the cylinder-top and using the piston-rod with a stuffed collar.
After Mr. Smeaton's time the water-pressure engine seem8 to have remained in abeyance, and I am not aware that any more of them were made until Mr. Trevithick revived their use, in constructing several water-pressure engines, one of which was erected in Derbyshire in the year 1803, and is still, I believe, at work (in 1848) at the Alport mines, near Bakewell, to which place it was removed from its original situation, not far distant.[
Trevithick thus speaks of it, in a letter written at the commencement of 1804:—
It has been at work about three months, and never missed one stroke, except when they let a tub swim down the descending column.
In a subsequent letter he complains of non-payment for his foreman's attendance and travelling expenses, and for the wages of the men he sent, adding,
If they found fault with the engine there would be some reason for not paying, but they say it is the best in the world.
The cylinder was 25 inches in diameter, with a 10-feet stroke, in which the water column gave a pressure of 75 lbs. on the square inch; and was fixed underground at the adit level, 48 feet above the bottom of the mine, giving motion to two large pumps, each 33 inches in diameter, with a stroke of 10 feet, lifting water height of 48 feet.
This pressure-engine was double-acting, or of equal power on the up as on the down stroke; the pumps gave their weight only on the up-stroke. A balance-bob placed at the surface equalized the powers the descent of the weighted box assisting the up-stroke of the pump-rods. The valves were nearly the same as in the Druid pressure-engine. The water raised in the pumps was equal to the combined effect of the descent of the balance-weight together with the upward stroke of the pressure-engine.
This early machine, working night and day for half a century in the bowels of the earth, exerted a power greater than the large and overrated steam-engines of Watt.
Trevithick's water-pressure engine had a force of about 16 tons; the Watt Dolcoath great engine, with its 63-inch cylinder and effective pressure of 10 lbs. on the inch, had a force of 14 tons, but this was only exerted on the down-stroke, the engine exerted no power during the up-stroke. The water-pressure engine to do the same kind of pumping-work gave out power from both the up and the down stroke, a compound stroke giving a power of 32 tons. This simple, durable, and cheap water-pressure engine, with all its disadvantages of position, was thus more than twice as powerful as the great Dolcoath steam-engine of Watt.
The writer has introduced this lengthened account of the plunger-pole pit-work and the water-pressure engine to make good a seeming void in mechanical history. The former is still universally used, the latter has to some extent been put aside for the more easily applied steam-engine, though the writer in 1831, at the Hayle Foundry, made drawings for a 10-inch pole water-pressure engine, 7 feet 6 inches stroke; the pole-case 1 inch larger in diameter than the pole; the head of water was 300 feet, giving a pressure of 150 lbs. on the inch; the inlet and outlet valves were 41 and 51 inches in diameter, double-beat, worked by a plug-rod and cataract; the general outline was a copy from Trevithick's work of thirty years before.
A thorough knowledge of mechanical movements was one of Trevithick's greatest acquirements, and the correct application of the mechanical powers a matter of comparative ease in his hands. His Wheal Druid engine worked at a pressure of 100 lbs. on the square inch — a force but seldom used in our modern stationary engines. It must be considered that, not only was he single-handed in his daring inventions, but, at a time when wooden pipes were still much used in water-works, and iron pipes and machinery of very rude construction, be was compelled to turn manufacturer, oftentimes having to utilize the larger portion of an old machine in the construction of a new one.
The following tradition of Mr. John Harvey, the father of Mrs. Trevithick, and founder of the Hayle Foundry Engine Works one hundred years ago, opens our eyes to the immensely greater difficulties in the path of the engineer in those days as compared with the present time. Trevithick, sen., is spoken of in a former chapter as having gone to Bristol and elsewhere for iron pipes in 1775; for the use of iron had not at that time wholly driven out the wooden pipes from the Cornish mine pit-work.
On a Sunday morning, in the year 1770, a rich friend of Mr. Harvey's came into his smiths shop, at Carnhell Green, having lost one of his silver shoe-buckles when taking a run with his beagles before church time, and said, "How can I go to church with one buckle?” “Give me one of your old silver spoons, and lend me that buckle, and I'll soon set you up again," said John Harvey. The rich man was pleased, and asked what his friend would do if he had some of his money. "Why, go down to Foundry, and make cast-iron pumps for Trevithick's mines in place of the wooden ones."
Another story says, that Mr. John Harvey went up the country to see how castings were made. Having been refused admittance, he dressed in rude clothes, feigned to be half-witted, idled about the doors of the foundries, singing songs, and now and then ventured in; offering to carry water, or errands, and so discovered how to make cast-iron pipes.
Mrs. Edwards, of Perran, in St. Hilary, when a girl, used to go with Betsy Edwards to Hallamanin Mine when site carried dinner to her father and brother, about 1798. They worked in the carpenters' shop, boring out the wood pumps, and we used to carry home the borings for lighting the fire. Captain Trevithick was the engineer. I recollect him very well; he was a tall, thin man. It was about that time that the Brumagem company had to give in, and Captain Trevithick started the mine again.<
This was one of the numerous mines in which the Watt low-pressure and Trevithick high-pressure fights were contested, on the first working of high-pressure steam-engines. It is curious that this battle-ground was within a mile of the heap of stones forming the grave of the old granite boiler at Gwallon Mine, and but a little farther from Ludgvan-lez, where Newcomer had erected one of his earliest engines, which in course of time was replaced by a Boulton and Watt — the old mine-heaps are now called Wheal Boulton — while just across the valley, at Hallamanin, worked a Trevithick high-pressure steam-engine.
- Enys "On the Cornish Engine," Trans. Inst. C. E.,' vol. iii.
- Ibid. Appendix G to Tredgold. Pole 'On Cornish Engines,' p. 112. The plunger-pump was invented by Sir Samuel Morland, and patented by him in 1675 (p. 115).
- Nich. Journ.,' No. 7, N.S. Gregory's 'Mechanics,' p. 196, vol. ii., published 1806.
- Lean's 'Historical Statement of Steam-Engines in Cornwall', published 1839.
- Residing at Penzance, 1869.
- Residing at Redruth, 1869.
- In Watt's time called Wheal Chance; then Prince William Henry; and in the present day Roskear Mine.
- Mr. Symons resided at Camborne in 1868.
- Resident in Penzance in 1869.
- Report on Water-pressure Engines by Joseph Glynn, F.R.S., M.Inst.C.E., &c. Published by the British Association for the Advancement of Science, 1849.
- See calculation in Stuart's 'History of the Steam-Engine,' chap. iii, p. 27, giving 8.5 lbs. effective pressure.
- Banfield's tradition, related in 1869.
- Recollections of Mrs Edwards, living at Perran in 1869
TREVITHICK'S PLUNGER POLE PUMP, 1797.
- a, the pump-rod, of wood fastened into the hollow cast-iron pole;
- b, the pole or plunger;
- c, the pole-case allowing space for the passage water round the pole;
- d, the stuffing box;
- e, the bottom valve, allowing the mine water to ascend into the pole-case on the ascent of the pole;
- f, the top valve, through which the water is forced upward on the descent of the pole.
TREVITHICK'S DERBYSHIRE WATER-PRESSURE DOUBLE-ACTION ENGINE OF 1803.
- a, the water-pressure cylinder, 25 inches in diameter, 10-feet stroke, working at a pressure of 75 lbs. to the inch;
- b, the piston;
- c, piston-rod cross-head;
- d, rod from cross-head to the balance-bob fixed at the surface:
- e, balance-bob and box for counterpoise;
- f, guides for piston-rod crosshead;
- g, two pump-rods descending from the piston-rod cross-head to the pumps;
- h, the two pumps, each 33 inches in diameter, raising water from the bottom of the mine to the adit level, about 48 feet;
- i, the water-pressure pipe, 15 inches in diameter, bringing the water from the surface down to the engine fixed at the adit level, a depth of 150 feet;
- j, the two piston-valves shown in the drawing as allowing the pressure water above the piston to escape to the waste-pipe, while the other valve allows the pressure water from the column to pass through the pipe k to the under side of the piston—the change of position of the valves reverses the action; the pressure water from the column is turned or fob the top of the piston, while that below the piston passes back through the pipe k, and escapes through the waste-pipe;
- k, the pipe communicating from the pressure-pipe and waste-pipe with bottom of the cylinder;
- l, the waste-water pipe;
- m, a wheel over which a chain passes, with movement to the rods from the two piston-valves;
- n, lever and rod connecting the valves with the tumbling beam;
- o, tumbling beam, moved by tappets on the main rods, the weighted part accelerating its movement when the weight p leans on either side of the centre;
- p, balance-weight, causing the lever to fall quickly just before the finish of the stroke; * q, rests on which the ends of the tumbling beam fall;
- r, plug-rod attached to the main rods, on which are the two shifting tappets for lifting or depressing the end of the tumbling beam just before the finish of the stroke.
- The pressure column had a valve at the surface, so that by contracting or increasing the supply of water, the speed of the engine w as decreased or increased. The valves may have been worked wholly by the tappets, or modified by the balance or tumbling bob, or by the use of a cataract, — all three methods having been engines.