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first cost which would at the same time there is a movement in favor of a system be entailed; while the difficulty of main- by which considerable power is obtained taining a good vacuum increases, as also from a small motor. Of this type a does the proportionate work done by the brief description of the Brotherhood enair pump, as the size of the engine di- gine only will be given, as engravings minishes. This fact has an important and descriptions of the others are to be bearing on the pressure used; for it must found in comparatively recent numbers be remembered that the effective press of various engineering journals. ure is the difference between the forward Fig. 6 is a section through the three and the back pressure, the latter being, cylinders of a Brotherhood engine; the in the above cases, nearly constant. Low crank being balanced by a counter weight forward pressures must be very wasteful, A, and the three connecting-rod ends the limiting case being when the for merely butting against the crank pin, to ward and back pressures are equal, for which they are held by two steel rings. then the whole imparted heat would, in The valve is a rotary one, and its action a non-condensing engine, be absolutely is shown in Fig. 7, which is a longitudithrown away.
nal section. The steam is being ad
(1.) These engines have been largely introduced for high speeds, so as to save the necessity of intermediate gearing, and to develop considerable power with a small motor. They almost invariably have multiple cylinders, generally three, as in the well-known Brotherhood example, and in those of Watt, Wigrell and Hasley, and Willans; while Vosper's. engine has four. The steam only acts on one side of the piston. The great advantage of this is, that there is no shock from the wearing of the connecting rod ends, or “backlash," as it is called. This is most important, at the almost incredible velocities at which some of these mitted to the top of the piston by the little motors work-many by the first- port J, the opening in the valve putting mentioned maker working at 1,400, and it in communication with the steam some even at 1,600 to 1,800 revolutions chamber G. The exhaust is made by the per minute. Moreover, the piston rod passage N' being placed in communicaand guide blocks are dispensed with, and tion with the annular space in which the parallel motion is secured by having a crank works, and finally escapes through deep piston, to which the connecting rod the exhaust pipe, Q, placed at the botis attached, and thus compactness is ob- tom of this chamber. The steam presstained; the absence also of eccentrics ure was about 70 lbs. per square inch, and eccentric rods renders the working with 250 revolutions per minute. The parts few in number, while the use of the compression, which commences rather flywheel is entirely obviated. Of the before half-stroke, can scarcely be a numerous forms, that of Brotherhood source of loss, as it allows the entering has by far the most extensive applica steam to rise to the full pressure at once, tion; and it may be said that the one and certainly results “in the complete exhibited by the inventor at the Vienna suppression of all species of shock." Exhibition, in 1873, which gained a sil- This, in a single-acting engine, with no ver medal, was the first of the class of arrangement for tightening the connectwhich several hundreds have been made ing-rod bearings, is a desideratum. The by him alone, and a large number by wire-drawing, obvious from the diagram, other inventors, who have since worked is the result of the circular valve, which, in this direction. It is thus seen that I advantageous as it is for many reasons,
DOUBLE-ACTING STEAM ENGINE.
is not moving at its greatest speed as with the ordinary slide valve, when the engine is near its dead centers. Fig. 8 (2.) The second class of small engines, shows the period of its action. The ef- viz., those which are double acting, ficiency of the machine itself, that is the and generally work with a single short ratio of the indicated work to that ob- D-slide-valve, are at present by far the tained at the brake, is 75 per cent. The most common, and a section of one of developed power was 10 HP. It is to be this type is shown (Fig. 3). Now, alregretted that no determinations of fuel though the forming is made to take and steam used were taken. But al- every concievable shape, and they are though it has been asserted that these made to work in every position, and have engines are wasteful of steam—and cer- slight differences of detail, yet the printainly the length of steam passage must ciple of action is the same, and is so well entail a loss—yet on some trials made by known as to need no explanation. The
the Royal Engineers, in which these en- point of cut-off of the steam is irom & to gines were used to drive Gramme ma- of the stroke, the corresponding grade chines, the consumption of steam was of expansion being from 1 to 1}, and 41.1 lbs. per hour per HP.,* revolutions more expansion than this cannot be 500 per minute, pressure of steam 80 lbs. economically effected with a single per square inch, about 13 HP. being de- valve. The two engines before referred veloped. This agrees with the consump-Ito cut off steam at about the latter point. tion of steam obtained by officers of the The details of the experiment were as French navy, which, the inventor states, follow : Both the indicator and the dywas 40 lbs., and is equivalent to an ex. namometer were used, the latter being of penditure of from 4.5 to 5 lbs. of coal the ordinary form, that is Prony's dyna. with a good boiler, or 8 lbs. with one of mometer lined with blocks of elm, emthe type already examined.
bracing pullies respectively 2 feet 7
inches and 3 feet in diameter in the two • "Engineering," vol. xxiii., p. 320.
No. 1 was a vertical engine, and
was bolted to the boiler. No. 2 was that the final efficiency of the whole is horizontal, and rested on a foundation of only about 0.19 in No. 1, and 0.3 in No. brickwork and stone. The number of 2, that is theoretically possible for an enrevolutions varied to some extent, but gine using steam at those pressures and were taken every quarter of an hour. with those grades of expansion, but em
ploying a condenser and having a boiler Fig. 8.
of 0.7 efficiency.
An ingenious kind of steam engine is used in the engineering laboratory, University College, London, invented by Mr. H. Davey, M. Inst. C.E., of Leeds, which is the only one of its class yet made. A small yuantity of water is injected at each stroke into a coil of pipe heated by
a furnace, and is at once converted into The experiments would perhaps have steam, and so drives the engine, which is been more satisfactory if a speed counter single-acting, about HP. heing dehad been applied, since with a brake on veloped. Improvements are being made a small engine the action cannot be kept in the design, and Professor Kennedy, perfectly regular, and the governors M. Inst. C.E., thinks the invention a were purposely disconnected. However, promising one. the following Table is without doubt a Small oscillating steam engines have near approximation to the truth: been used, but the admission and release
TABLE OF DATA FROM ENGINE TRIALS.
47.2 42.32 14.30.035 0.013 45.3 44.0 9.2 0.039 0.022
These results show that in this class of of steam, to be effected economically, engine, at any rate, the consumption of require rather complicated valve gearfuel is at least from four to seven times ing. greater than in the best kind of large en There is another class of double-actgines, and that it is therefore beside the ing steam engines which are not rotative, question to quote the performance of and since merely reciprocating action is large engines when comparing the work. obtained, the slide-valve has to be driven ing cost of small motors. In connection by some arrangement other than an ecwith the indicated power of No. 2, which centric. Such engines are often used as is less than the nominal, it is only fair to donkey pumps and often as steam rockstate that the engine often works with borers. An instance of the former is the about 40 lbs. pressure and 180 revolu. “Special Steam Pump;” a description of tions, which would cause it to indicate its action is to be found in the pamphlets more than 6 HP. A similar remark ap- of Thurston or Evers on the steam enplies to No. 1. Again, it is well to note gine.
STEAM ACTION ON FLUID SURFACES.
tions, and, finally escaping at T, A, A, (3.) It was stated in “ Engineering,” give motion to two similar discs, which six years ago, that “most mechanical act as the pump by a similar action, and engineers now-a-days have a deeply-root- so great compactness is obtained. The ed antipathy to rotary engines.
Nor method of packing is ingenious and efhas the appearance of any successful fective, and is formed by the metal pieces patent between that time and this caused B, B, being pressed outwardly by an alteration in opinion. Rotary engines springs, their centrifugal force acting are understood to be those which obtain
with a similar effect. Behrens' engine circular motion directly by the action of is similar in action, and is much used in
America as a pump. steam upon some revolving piece, and so avoid the necessity for the conversion of reciprocating into circular motion. It is not to be wondered at that a large num
(4.) Two kinds of action are used. ber of ingenious attempts should have The first, Mr. Bramwell, F.R.S., M. Inst. been made to thus obviate the use of the C.E., has said, is expressed by one word crank and the connecting rod
For in. “Concentration," and may be said to act stance, thirty years ago, one of the form by impulse, to which belong the Giffard known as a
disc engine, was for Injector and the Inspirator. The second some years years used to drive the print- uses the principle of the Savery, engine ing machinery in “The Times” office, and acts chiefly by pressure, of which and is described by Rankine;* but al- the Pulsometer and Pulsator are types. though according to that author “the As before stated, this class of apparatus number of rotatory engines which have is employed for pumping purposes, and been patented in Britain alone is certain this may be said to be its exclusive duty; ly upwards of two hundred,” yet “ very its use in this direction is increasing, and few have been brought into practical whenever there is a supply of steam the operation, and those to a limited extent simplicity of action and remarkably only; for their friction and liability to small weight and size of the whole mawear have been found to be greater than chine are great recommendations. those of ordinary engines, and they have
The theory of the action of injectors is no advantage except compactness.
now well known, so that it will not be There is, however, one purpose to which necessary to describe any one of the they have recently been applied with numerous forms in use, although a refersome success, viz., to fire-engines, where ence to Hancock's inspirator may be economy of fuel, which the difficulty of made. This little instrument is becomkeeping the revolving portion steam-ing very popular, as it admits of accutight renders impossible, is not the chief rate adjustment, after which little attenpoint, and where the use is only occa- tion is required; while the weight of one sional, and so the wear not of the first capable of feeding a 48-HP. boiler is importance. Fig. 9 shows a simple only. 6 lbs. The undoubted function of
all'injectors is the foregoing, viz., the
feeding of boilers, and they are universFig. 9.
ally applied to locomotives for this purpose.
The second kind are really steam vacuum pumps. The “Pulsometer” is a very successful example. The action is automatic and alternative, and the arrangement is, in fact, a self-acting Savery engine. As with the Savery engine,
however, the consumption of fuel is conform which is used for this purpose. cinnati Exhibition in 1875, quoted by
siderable. Trials were made at the CinHere the steam entering at S drives Mr. D. K. Clark,* and at the Friedrich round the discs A, A, in opposite direc- Lead Mine, Upper Silesia, recorded in the
*“A Manual of the Steam Engine and other prime movers," p. 504.
*"A Manual of Rules, Tables," &c., p. 969.
ROTARY STEAM ENGINE
Abstracts of Foreign Papers.* In the The original method of using gas in former case, 53.1 Ibs. and 43.4 lbs. of this way was to admit it to the cylinder coal per hour per HP. for water actually of the engine, together with air in such raised were expended on two respective proportions as to form an explosive mixtrials; in the latter 52.4 lbs. of slack ture, which was ignited, and work obwere used for the same amount of work; tained by the consequent expansion. but in the latter trial a “ Tangye” pump Lenoir's engine, which was one of the consumed 40.5 lbs. for the same duty. first, resembled an ordinary horizontal The conclusions drawn from this trial, engine, effecting the ignition by an elecand other data obtained by experience, tric spark; but the difficulty of utilizing were that the total outlay for stores and this sudden effect was a cause of conrepairs with pulsometer was 1.68d. per siderable loss, and it is stated by a Gerhour per HP., that for the piston pump man writer on the subject* that 3 cubic being 1.44d.' The great recommenda- metres (about 106 cubic feet) of ordition of the former, however, is its porta- nary coal gas are required per hour per bility, as it is as well able to work when HP. for a small sized engine. This corslung by a chain as in any other way; responds to the figures quoted by Mr. D. also it will, in the words of the advertise. K. Clarkt from the experiments of M. ment, “pump almost anything,” includ. Tresca, two successive trials of this ening tar, sewage, chemical liquids, and gine, giving 112 and 97 cubic feet reeven liquid cement, and is one-half spectively, the mean of which is 104} cheaper in first cost than an ordinary cubic feet per hour per HP. at the brake, pump of equal power; thus there is evi- being an efficiency of little more than 4 dent reason for the extensive sale which it per cent. Though this engine had an enjoys. A recent modification, under extensive sale in Europe, it was 10 a the name of the “Hydrotrophe,” is be- great extent superseded by the Otto and ing employed to feed boilers, and both Langen motor. In this the sudden exthis and the injector must be economical, pansion of the gas was allowed to raise a 'the surplus heat imparted to the water piston against the pressure of the atmosbeing returned to the boiler.
phere alone, which pressure, upon the cooling of the heated gas in the cylinder
hastened by a water jacket, drove down Gas is a convenient source of power; the piston and so performed work, the and in towns, where it is already sup- piston-rod being a rack which geared plied almost to every building for pur. with a pinion on the horizontal shaft. poses of illumination, it is at once ob- This engine is a regular and efficient motainable in any moderate quantity. tor, and its consumption of from 22 to Moreover, the principle of adopting a 30 cubic feet of gas per hour per HP. is large centre of supply, which is em- vastly superior to the Lenoir engine, and ployed in the case of gas, is, on scientific is even less than in some engines which grounds, truly economical, for that sub have superseded it. One engine, which stance is supplied in the state of fuel, has been at work for ten years in Bristol and involves no more loss in its trans- is in good condition, and has cost durmission than would occur in the trans- ing that period very little for repairs; ference of any other fuel. But in spite but its noise in working is much against of many attempts to use it for small mo- its general adoption. Again, it is necestors, it has only recently been much sarily a vertical engine, by no means so adopted. Air is used in a peculiar way popular as the horizontal form, and 18 in the gas engine, and it is only in a simi- anthing but compact. Thus when the lar way that gas can be profitably em- new engine of Otto was introduced into ployed, viz., as the working agent, at this country by the same manufacturers, the same time as the source of power; for Messrs. Crossley Brothers, of Manchesthe calorific power of gas, taken in con- ter, which was at once compact, econojunction with its present cost, at once mical, and above all, silent, they almost puts out of the question any idea of us. at once ceased to make the Otto and ing it as a direct substitute for coal.
*“ Klein-Kraft-Maschinen," p. 27. Von Peter Hell, * Vide Minutes of Proceedings Inst, C.E., vol. lvi., Braunschweig:
7" A Manual of Rules, Tables," &c., p. 921.