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MR. R. MALETT'S NEW LONG VALVE AND MAIN FOR ATMOSPHERIC RAILWAYS.

VOL.

Mechanics' Magazine,

MUSEUM, REGISTER, JOURNAL, AND GAZETTE.

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XLIII.

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MR. R. MALLETT'S NEW LONG VALVE AND MAIN FOR ATMOSPHERIC RAILWAYS.(SEE CURRENT VOLUME, MECH. MAG. P. 232.)

THE objects in view are to diminish the cost of the main and valve, simplify their parts, and diminish leakage which occurs to so great an extent with Clegg's valve. The main is cast with a pair of jaws, one on either side of the long slot, through which the coulter travels. These jaws are formed to a particular curve, (see fig. 1,) and are cast against "a chill" by which they are obtained perfectly smooth, fair, straight and hard, and thus the cost of " planing" the valve faces is avoided. The valve consists of a continuous-hollow tube or hose, of woven hemp, coated throughout with caoutchouc, like the tube of a stomach pump, or other such instrument. This tube is maintained full of water or brine in cold climates, and when it is closed as a valve, is forced in between the jaws of the main, and acts like a sort of continuous cork. As the coulter, &c., travels along, the tube is lifted up a few inches out from the jaws, by suitably formed rollers, and as soon as the coulter has passed, it is pressed back again into the cavity between the jaws by a roller pressing upon its upper surface.

In place of a hollow hose full of fluid under a constant small head, or of compressed air, a compound continuous cork formed of four cotton ropes embedded in caoutchouc. This is, in fact, one of Brockedon's patent stoppers of indefinite length. Either arrangement would admit of sufficient extensibility in length to allow the lifting up and pressing down of the valve at the passage of the coulter without injury.

The outer surface of the valve, in either case, should be coated with an unguent, which will not act on the caoutchouc; if vulcanized India rubber be used, com. mon palm oil will answer. Pinkus's valve was a continuous flat band of leather, and failed, because when close, it had no tendency to keep in its seat, and its edges were thrown up by the pressure of the atmosphere on its centre part.

Hallette's valve consists of two continuous tubes full of compressed air, by the elasticity of which they are forced against each other, and the main thus attempted to be made staunch; but the serious defect appears to be, that the tendency of the atmospheric pressure upon the outside of these artificial lips is

to force them asunder, so that the exhaustion of the tube tends to produce, in place of to diminish, the leakage of the valve. The present contrivance, which has something in common with both Pinkus's and Hallette's arrangements, through invented long before the latter published his plan, appears free from the disadvantages of either, and to possess several advantages not offered by any other valve proposed.

The letters refer in common to all the figures. Fig. 1 is a transverse section of the improved main and valve. a a is the main; b b, the valve seat, the opposite faces chilled; c, the tubular valve in its seat; when raised at the passage of the coulter it assumes its cylindrical form, as shown in dotted lines, d d d d, passing over the sheaves, or rollers m, &c.; t is the coulter seen endwise; h, the rib of the travelling pis

ton.

Fig. 2 is a plan and section horizontally of the atmospheric main, a a; bb, the valve seat or jaws, cast with "chilled" faces-(these are best seen in section, fig. 1.) The lengths of main are put together with abutting rabbeted flange, or rather lugged joints, at every 15 feet, with a flange of India rubber inch thick between, the elasticity of which allows for expansion of the main, and yet keeps the joint air-tight.

Fig. 3 is a horizontal section of the tube, and plan of the piston.

Fig. 4 is a vertical section of the tube, and elevation of the piston.

Fig. 4a is an elevation of the entrance of the tube.

Fig. 5, transverse section of the valve as raised; fig. 6, a transverse section of it as closed; fig. 7, a transverse section on the line A B of fig. 4; and fig. 8, a transverse section on the line CD of fig.

4.

From the facility given for support of "the cone," by the "chill," for casting, the valve seat faces on the main, as thus designed, can be as readily cast in 15 feet lengths as in 9 feet, which has been the limit of Samuda's practice. c is the tubular valve of woven hose, covered with caoutchouc, or of caoutchouc and cotton solid: it is here shown hollow, and is maintained full of water by a small flexible tube d, at either end of the section of main joined to the extremity of the

MALLETT'S NEW LONG VALVE AND MAIN FOR ATMOSPHERIC RAILWAYS. 307 Fig. 2.

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feet of water, by which the tubular valve is always kept full and plump." This little supply tube is so placed as to be passed by the coulter, &c., and to permit the valve to be lifted up and pressed back again into its seat. g is the travelling pi ton-head; h, the rib or frame of the travelling gear; k, the balance-weight; l, m, n, o, the hollow grooved rollers, made like ordinary sheaves," which gradually lift the tubular valve out of its jaw-shaped seat, to permit the coulter to pass with the piston; the first and last of these, and o, are narrow enough to pass up between the jaws, or into the longitu tudinal slot, and are of hardened steel; r is the roller, with a slightly concave edge or rim, which, attached to the porch of the leading carriage s, presses down the tubular valve into its seat, something like forcing a continuous cork into the neck of a bottle, and so leaves the main ready for fresh exhaustion after the passage of a train; t is the coulter of plate iron five-eighths of an inch thick, carries the rollers, piston, &c., and attached to the perch s.

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Sir, I have read your account of the third voyage of the Great Britain in last week's magazine, and am both surprised and annoyed at the results there detailed. I learn from the account referred to that the consumption of fuel is 63 tons per day, which, if employed as it ought to be, should give out fully 900 horses power without any extraordinary degree of expansion; but we are told the steam was generally cut off at 13 inches of the stroke, so that it must have expanded between five and six times; hence the power realized should have been very much above 900 horses. Mr. Guppy (the Director of the com- . pany, under whose superintendence these engines were made) stated, at the Institution of Civil Engineers, that the e steam was generally cut off at one-sixth of the stroke, (of 6 feet;) hence the statement, here referred to, of its being cut off at 13 inches, is no doubt correct. Now, to me, the unaccountable part of the affair is this: The boilers of the Great Western supplied sufficient steam at

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3 lbs. for 15 strokes, without working the expansion gear; and I know from indicator cards I have seen, that when so working, the cylinders of 72 inches diameter were filled six feet out of the seven with steam of 3 lbs. above the atmosphere. Now, at 15 strokes, the two engines of the Great Western would consume 10,177 cubic feet of steam per minute. The heating surface of the boilers of the Great Britain is about 8,500 feet, that of the Great Western was about 4,000 feet. The quantity of coal consumed in the latter was about 24 cwt. per hour, the former 53 cwt. in the same time; hence it follows that the quantity of steam generated in the Great Britain should be more than double that of the Great Western.

But if we take the diameter of each of the four, cylinders of the Great Britain at 88 inches and the revolutions at 14, we find that the quantity of steam that should pass through the engines in one minute (cutting it off at 13 inches of the stroke) is 5,096 cubic feet. Now, I should like to know what goes with the rest; for that a much greater quantity is generated I have no doubt, although not sufficient to produce the most satisfactory results, because the surface in the boilers should have been at least 12,000 feet.

I should advise Captain Hoskins to have his engines carefully examined by a practical mechanical engineer of known standing, conversant with the application of steam to marine engines. He will have found by this time that it is perfectly useless for Directors to become their own engineers, or the constructors of railways to attempt marine engine building.

I am, Sir, your obedient servant, London, Nov. 3, 1815.

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G. S.

HOSEASON'S LETTERS ON WORKING STEAM EXPANSIVELY IN THE ROYAL NAVY.

Sir, I have just read your reprint of Mr. Hoseason's letters to Sir W. Parker, C, with Binnacle's eulogium, and your commendation thereon.

Although I admire talent in any grade, and have always looked favourably on the efforts of the Otways, Hoseasons, and others, for the benefit and enlightenment of their benighted navy brethren in the

THE PRINCIPLES AND PRACTICE OF DRAINAGE.

science of the steam engine, still it is going rather too far to allow them to appropriate to themselves as their individual inventions, the most common laws and fundamental rules of civil engineering, as applied to marine purposes.

The work published by Lieut. Otway is so full of glaring errors in almost every page that it would be necessary for the naval student to unlearn almost every thing he had there imbibed, before he could enter on a sound course of instruction.

Let us now advert to the letter of Lieutenant (now Commander) Hoseason to Sir W. Parker, republished in No. 1158. We there find him accounting for, and explaining the statement of Captain Oliver," that in the Phenix he could, full consumption, steam only 9 knots, and half consumption, 7 knots," in this sort of a way, that "the resistance of fluids is as the squares of the velocities,' consequently 72 = 49 and 92 = 81, or nearly double! Surely, comment is unnecessary on so absurd a figment as this.

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If he had told his brethren, that "the required horse power is as the cubes of the velocities," he would merely have disseminated a fact that has been known to marine engineers for many years past, almost before steam was used in the navy, and subsequent practice has so proved this rule that no doubt exists of its truth. We elucidate it by the statement of Capt. Oliver.

The Phonix (at the time referred to) was fitted with Maudslay's engines. Cylinders 55 inches diameter, and 5 feet stroke; therefore collective power = 110 horses. The maximum velocity is stated to have been =9 knots, and with half consumption =7 knots.

The cube root of 100 is 479*

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309

Mr. Hoseason writes as if the theory of expansion was a new thing; in fact, that he had almost discovered its practical application: this is a fallacy that he will do well to forget; it was known to engineers and is to be found laid down by competent authors many years before his time; nay, it had been practically used in private steamers.

If his friends claim for him the mere reiteration of known principles, upon the dull comprehensions of Lords of the Admiralty, he has undoubted merit-although in this Otway certainly took the lead. I mean when he was in command of the Echo, fitted with Cornish boilers, working under a pressure of 15 lbs., and expanding about two-thirds of the stroke. (See his book published by Sherwood, 1834.)

Within the last three years, it was a rule of the Government engineers "that no boiler should work under a greater pressure than 5 lbs. per square inch." What then are engineers to do with such absurd regulations as this pressing upon their exertions? It is well known that in private vessels a much higher pressure is used with a great degree of expansion, and of course, corresponding economy in the consumption of fuel.

These remarks are not written with any ill feeling towards Lieut. H., but I think he claims far too much.

I am your obedient servant,
PRESSURE NOT PUFF.

THE PRINCIPLES AND PRACTICE OF
DRAINAGE.

[Concluded from page 331.]

"From the above premises it follows, that where a given quantity is to pass off, the greater the section is, in which it passes, the less inclination or difference of level will suffice, or on a given difference of level, the greater the section the more will pass.

"The section may be increased by widening, but if it runs shallow, suppose 1 foot deep, on 20 feet wide, if the width is increased to double, it will undoubtedly, on the same inclination, run a double quantity, viz., it will act as two drains of 20 feet (or nearly so) but if you dig the 20-foot canal I foot deeper, so that the area of the section of its water may also be 40 square feet; in the latter case the whole body of water will be contained in a circumference of 24 feet, whereas in the former it will be surrounded by 42 feet; and as a great deal of impediment

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