Abbildungen der Seite
PDF
EPUB
[graphic]

Mechanics' Magazine,

MUSEUM, REGISTER, JOURNAL, AND GAZETTE.

SATURDAY, JANUARY 15, 1842.

[Price 3d.

Edited, Printed and Published by J. C. Robertson, No. 166, Fleet-street.

HENSON'S PATENT CONDENSING STEAM-ENGINE.

[ocr errors]

92

ON

Fig. 4.

D

Fig. 2.

HENSON'S PATENT CONDENSING STEAM-ENGINE.

Description by the Inventor.

The improvement by which this engine is distinguished from others, consists in permitting the escape from the cylinder, or from the steam passages between the cylinder and the condenser, during a very short interval of time near the termination of each single stroke of the engine, of so much steam as shall leave the remainder in the cylinder but little above atmospheric pressure, and condensing that remainder by the means ordinarily used in condensing engines.

Fig. 1, represents a front view of a steam-engine cylinder, with apparatus attached for working the common valves as well as that required for the peculiar purposes of this invention. Fig. 2 is a side view and fig. 3 is a horizontal plan of the same. Fig. 4 exhibits separately the cams which are shown in connexion with other parts by the figures 1,2, and 3.

A is the cylinder of the steam-engine. B is the piston, and b the piston rod. C is the steam pipe leading from the boiler.

D is the induction pipe.

E is the eduction pipe, understood to be continued as usual to the condenser.

d 1 and d 2 are the induction valves. e 1 and e 2 are the eduction valves. F1 and F 2 are the chambers through which the steam pipes communicate with the cylinder; and respecting which I would remark, that I prefer that the openings from them into the cylinder, and the chambers themselves, should be larger than usual.

G1 and G 2 are the escape valves; they cover corresponding openings in the chambers F1 and F 2, by which part of the steam escapes into the atmosphere, according to the design of my invention.

g1 and g 2 are springs which assist the return of the valves GI and G 2 to their

seats.

Having now indicated the principal parts of the apparatus, I will point out their movements; and in so doing I shall always suppose that the steam used is considerably above atmospheric pressure. During the greater part of the downward stroke of the piston B, the upper escape valve G 1 is held firmly to its seat by the

• Patented July 16, 1841.

action of parts to be described hereafter. When the piston has nearly reached the end of its stroke, the pressure is removed from the valve G 1, on which the excess of the pressure of the steam in the cylinder, over that of the atmosphere, opens the valve; and so much steam escapes as that the pressure of the remainder is equal to that of the atmosphere, together with the force of the spring g 1; the valve G 1 then closes, and the eduction valve e 1 is opened, which admits the remaining steam to the condenser, and a vacuum is formed in the cylinder in the ordinary manner of condensing engines. In the upward stroke, the corresponding parts perform similar functions, as will be readily understood. By this means, the pressure of the atmosphere is removed from the side of the piston opposite to that on which the steam acts, which has not ordinarily been done in steam engines worked with high pressure steam. The movements of the valves above described are effected in the following manner by the parts I now describe. h is a shaft connected by the wheels h 1 and h 2, or in any other convenient manner, with the main shaft of the engine, so as to make equal revolutions with it. ii, are the bearings in which the shaft h turns; jj bars of the frame supporting the said bearings, and which are themselves secured by one end to the cylinder A; and by the other, to the upright, or standard, k k. an upright or standard affixed near its lower end to the base plate of the engine; and is a stay by which the upper end of k, k is firmly held in its place; m is a bar secured to the steam chests F1, F2, for supporting the centres of the levers o 1, 02. HI and H 2 are two levers, whose centres are in one line, and are supported by the upright k. H 1, the shorter of these, carries a truck or roller, which applies to the cam No. 3. H2, the longer lever, carries a similar truck, which applies to the cam No. 2; n 1, n 1, is a rod which passes through stuffing boxes in the valve chests F 1, F 2, and is attached to the valves e 1 and e 2, being itself actuated by the lengthened extremity of the lever H 2 pressing against the collar formed on the rod; n 2, n2, is a rod attached to the lever H 1, and ac

kk, is

HENSON'S PATENT CONDENSING STEAM-ENGINE.

tuating the levers n 3, n 3, whose centres are in the upright K, and whose extremities move the valves d 1, c 2 by their stems moving through stuffing boxes in the steam chests F1, F2, as shown in the drawing. The moving apparatus for actuating the valves, which I have so far described, only effects such opening and closing of the valves as is common to, and required by, all condensing engines; the shape of the cams No. 2 and No. 3, necessary for that purpose is shown by fig. 4.

The cams 2 and 3 are made fast on the tube 4, which is put over, and can turn on the shaft h, and on which is the journal which carries the front end of the compound shaft. The plate 5 is also secured on the same tube, but is outside of the journal; beyond it projects the shaft h, on which is fastened the cross bar 6, carrying at each end the click 71 and 72; in the edge of the plate 5 is formed a long notch or fall, as shown in the figure; and on its face is fastened the stud and handle 8. When, as in the figure, the cams are intended to turn with their upper edges moving from right to left, the stud 8 is brought against that part of the cross bar which appears lowermost in the position of the parts as drawn, and the click 71 is forced by its spring into the fall or notch, so as to abut against one end of it; when it is desired that the engine shall turn the other way, the cams will be brought into the right relative position by releasing the click 71, and turning round the plate 5, and tube 4, with the cams it carries, until the stud 8 comes against the other part of the cross-bar 6, and the click 72 abuts against the other end of the fall in the plate 5. o 1, 02, are levers carrying trucks which apply to the cam No. 1 respectively at the opposite ends of its vertical diameter, and by which through other parts the escape valves GI and G 2 are at proper times confined and set at liberty. They are connected with each other by a spring, o 3; p 1, p 2, are connecting rods, q1,q2 are levers, whose centres are supported by the upright k, and which are connected by the rods p 1, p 2, with the levers o 1, o 2, respectively, as shown in the drawing; r 1, r 2, are levers jointed by one end to q 1 and q2, and each carrying at its other end a strong pin or stud, which enters the slot in the stem s 1 or s 2 of its respective escape valve G 1 or G 2;

35

t1, t2, and u 1, u 2, are the bearings in which the stems s 1, s 2 of the escape valves slide.

It will be readily seen that when, as in the position represented in the drawing, the smaller part of the cam No. 1 comes to the truck or lever o 1 (which should be when the piston is near the bottom of the cylinder), that lever will be depressed, and by means of the rod p 1 will bring down the joint by which the levers q 1 and 1 are attached to each other, and thus withdraw the stud on the lever r l from its pressure against the end of the slot in the stem s1 of the valve G 1; the valve being thus released gives way to the pressure of the steam in the cylinder, and permits the escape of part of it as above described. During this time the larger part of the cam No. I holds down the lever o 2, by which the rod p 2 has been made to depress the joint of the levers q 2 and r 2, so as to bring thei nearly into a continued straight line, and by this means the stud in the lever r 2 is strongly pressed against the end of the slot in the valve stem s 2, and the valve G 2 is firmly held in its place against the pressure of the steam in the cylinder. further rotation of the cam holds both valves close, and at the end of a semi-revolution the upper valve is held close and the lower one set at liberty, which the action of the engine as before explained requires. The spring o 3 raises the lever o 2 when permitted to do so by the hollow in the cam No. 1.

A

I will now recapitulate briefly the course of the valve movements, and the way in which they are effected. Beginning with the piston near the bottom of the cylinder, as shown in the drawing, the escape valve G 1, is first released by the truck on the lever O 1 falling into the hollow of the cam No. 1, and the excess of steam escapes into the atmosphere at once, or along such pipe as may be used to conduct it; an instant after, and nearly at the moment the piston reaches the very extremity of the stroke, the eduction valve e 1, and the induction valve d 2, are raised by the rise on the cam No. 2 operating on the lever H 2; about the same time the escape valve G 1 has closed by the pressure of the atmosphere and the spring g 1, and is soon held fast again by the cam No. 1. This state of things continues during almost the whole time of the up-stroke. When the piston has D 2

nearly reached the top of the stroke, the escape valve G2 is released by the hollow in the cam No. 1 then coming to the truck or lever O 2: when the piston comes to the end of the up-stroke, the rise on the cam No. 3 raises the induction valves d 1 and the eduction valve e 2, the valves e 1 and d 2 having been just

closed by the fall in the cam No. 2, and the escape valve G 2 having also closed, and being held fast by the cam No. 1. No further change takes place until the piston arrives near to the bottom of the cylinder, when the series of changes again commences.

Remarks by Mr. John Chapman, C. E. [Abridged from Report to the Proprietor of the Patent.]

The principal feature of Mr. Henson's plan I understand to be this: the permitting the escape of as much steam, or nearly so, as will escape into the atmosphere, from the cylinder, near the end of the stroke, and condensing the remainder of the steam in the ordinary

manner.

It is obviously important to ascertain in what time any given quantity of steam, of a certain density at the beginning, will escape into the atmosphere through a given aperture; for if it might possibly turn out, that this time was so great, as materially to interfere with the action of the engine, in this case any other advantages of the plan would be neutralized or overbalanced.

Mr. Henson has given no exact directions for the size of the aperture of escape. But assuming it to be in area about one-fourth larger than the usual size of steam pipes, taking the latter at one-fifth of the diameter of the cylinder, (and I see no reason why it may not be made yet larger) I find by calculation, that the necessary escape need not occupy more than one-tenth of the time of the stroke, which is time of the least value, since the crank is then very near the centres. If we suppose the aperture of escape to be duly proportioned to the pressure of the steam used, we shall certainly be doing no favour to the invention, if we calculate that one-tenth of the time of the stroke, or, what is the same thing, that the time occupied by the passage of the crank over 18 degrees, is the time employed in the discharge. Taking into account that the crank is then in a position in which the pressure on it really does very little in the rotary direction, and that the pressure of the steam is not withdrawn all at once, it will be seen that the power lost is very trifling; it is much under a fiftieth part of the power of the engine, and in many cases will not amount to half that quantity.

To consider next the comparative advantage. It should first be remarked, that the essence of the plan is, the getting rid of a quantity of steam by suffering it to escape into the atmosphere, instead of condensing it. Now it is obvious, that as the power by which it escapes is its excess of pressure above that of the atmosphere, there can be but little escape, and consequently little advantage, where low pressure steam is used: and as condensation is always employed in low pressure engines as well as in the improved engine, no advantage worth mentioning would follow the adoption of Mr. Henson's plan in steam engines of that class.

The case, however, is very different in respect of high-pressure engines working at full pressure. To their power it would add almost an entire atmosphere. It must, however, be remarked, that few existing engines are prepared, by the strength of their parts, to receive and transmit this additional power; but in many cases an equivalent advantage may be gained, by working the engine to its present power, with a smaller consumption of fuel. Suppose it were desired to work a non-condensing engine with an 18-inch cylinder, to the power of 40 horses, the steam must be 50 lbs. per square inch above atmospheric pressure. But by the adoption of this improved plan the same power would be produced by steam of 30 lbs. per inch on the safety valve. The expenditure of fuel in the former case would be 453 lbs. per hour, and in the latter 312 lbs. ; being a saving of 141 lbs. per hour, which at 20s. per ton for 12 hours per day, and 300 working days in the year, amounts to 2261. per annum.

From

this, however, is to be deducted the expense of water for condensation, where it cannot be had without payment. Such an engine would require about 30,000 gallons of water per day.

SMOKE BURNING.

A high-pressure engine, worked expansively, would be more economical in fuel than this improved engine. The engine now described would work to 40 horse power, if the steam were of about 784 lbs. per square inch total pressure (or 65 lbs. on the safety valve), and were cut off at half the stroke. Its consumption of coals would be about 270 lbs. per hour instead of 312 lbs., effecting a saving of a little more than one-eighth. The strain on the boiler would obviously be very great.

It is easy to see, however, that this kind of comparison may be carried to any extent, and made to present almost any desired results, by altering the suppositions as to the pressure and expansion under which the steam is worked.

It is however of consequence to observe, that on some occasions an economical use of steam may be effected, by combining the expansive principle with the escape of the extra steam; and by this means also the great inequality of pressure which forms an important objection in many cases to the use of expansive steam may be brought within tolerable limits, while to some extent its advantages are obtained.

If the improved engine with an 18 inch cylinder, be compared with a condensing engine of the same power, the advantage will be found to be considerable. One of forty horses' power, moving 200 feet per minute, will have its cylinder of 304 inches diameter: its consumption of water will be nearly 80,000 gallons per day, and of coal 400 lbs. per hour. The difference amounts to 50,000 gallons of water per day, which in many situations will be of very great importance, and 88 lbs. of coal per hour, which, at the rate above-mentioned, is equivalent to 1417. per annum.

As compared with both the expansion engine with condenser and the low-pressure engine, there is yet another saving of fuel to be effected by this invention. In those engines the heat of the steam which has done its work, is so combined with the water employed in condensation, that it can be recovered and used again to but a very small extent; perhaps onethirtieth of the fuel may be saved in this way by supplying the boiler with heated condensation water. In the improved engine the method may be adopted, which is already in use with good effect in some

37

high-pressure engines, of conveying away the discharged steam by a pipe which passes through the reservoir of water by which the boiler is fed. I suppose an eighth or a tenth of the fuel will be economised by this method.

These calculations will serve to show by example, the nature, and something of the extent of the advantages to be derived from this invention. It is clear that it is not applicable to low-pressure engines; and where the nature of the work to be done admits the unequal pressure produced by the extensive use of expansion, this engine will not be preferred; but in the numerous cases where regularity of action is indispensable, and in very many others where the supply of water is scanty, this contrivance, I think, will be of great value. Nor does it need scantiness of water to furnish a reason for preferring it, since its consumption of coals is considerably less than that of a condensing engine of the same power.

I conceive that a judicious combination of this invention with others of recent origin, would render a material service to steam navigation. It seems to me probable, that in the large transatlantic steamers a saving of weight in fuel and machinery might be thus effected to the amount of 150 or 200 tons. The great importance of such a result, not only to the current cost and returns of steam vessels generally, but to the practicable length of steam voyages, needs no remark.

SMOKE BURNING.

Sir,-Permit me to direct your attention to the accompanying paper by Mr. Robert Armstrong, on "Smoke Burning," as it appeared in the Mining Journal of the 8th instant, and to request its insertion, as it appears well entitled to the publicity which your columns will give it, on account of the great ingenuity it exhibits, and, as I propose, hereafter, making some observations on the new light it throws on an extremely difficult branch of the chemistry of combustion as applied to practice.

I am, yours, &c.

C. W. WILLIAMS,

Liverpool, January 11, 1842.

Sir, Fully agreeing with a remark lately made by an able lecturer (Mr. Davies) at

« ZurückWeiter »