1840.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



37.5 



Perhaps this is chieHy to be attributed to the circumstance of the long 

 stroke offering on most occasions greater convenience than a short 

 stroke. Much may be due also to fashion. The earliest application 

 of steam power was for the purpose of pumping water in the course 

 of mining operations, and in this sort of work a good long stroke was 

 found to be attended with considerable convenience and advantage. 

 In blast engines, and many other of the earlier applications of steam 

 power, the same result was manifest; the earlier habits and ideas of 

 engineers were therefore naturally associated with long stroke engines. 

 Moreover, the earlier manufacturers of steam engines had neither 

 good machinery nor good workmen; they could neither depend upon 

 the correctness of their proportions, nor upon the exactness of the 

 workmanship ; besides, timber and other inefficient materials were 

 formerlv employed to a considerable extent in the construction of en- 

 gines; from all which causes imperfections and irregidarities were 

 numerous in the earlier engines, and they were consequently very in- 

 efficient. As all these sonrces of imperfection and inefficiency operated 

 much more extensively against short stroke engines than against long, 

 it is no wonder that the latter soon obtained a preference, and that 

 the prejudice should still continue to exist, notwithstanding the same 

 causes are no longer in operation. At the present day, with our good 

 materials and workmanship, exact proportions and adjustments, a short 

 stroke engine will be found to work as accurately and as perfectly as a 

 long stroke engine. 



There is one very important circumstance to be kept in view as re- 

 gards long and short stroke engines; which is, that whenever an en- 

 gine of the latter description has hitherto been made, it has always 

 been considered necessary to keep the cylinder nearly of the same 

 diameter, as in the long stroke engine, and to cause the engine to make 

 a greater number of revolutions in proportion to the shortness of the 

 stroke, so that the piston in every case might travel at a nearly uniform 

 speed of about 200 feet per minute. Now, to a short stroke engine, 

 made on this plan, there may undoubtedly be many objections. The 

 more frequent alteination of the stroke — the greater loss of steam by 

 the more frequent filling of the passages and nozzles, and the clearance 

 at the top and bottom of the cylinder — the much greater angular mo- 

 tion of all the bearings and moving joints, thereby materially increasing 

 friction and wear — are all circumstances tending to lessen the efficiency 

 of a sliort stroke engine made iqionthis plan. It is clear however that 

 an engine made upon the principle, herein before laid down, is not 

 open to the same objections. 



And, as regard the speed of the piston in engines, whatever may be 

 the length of stroke, being regulated to the uniform standard of about 

 200 feet per minute, there can be no valid reasons given for such rule ; 

 no one can prove that double the above speed, or onlv one-half that 

 speed, might not be employed with equal or greater advantage ; it is 

 certain that in many steam engines of the transatlantic world the pis- 

 tons move at a speed of 30'>, tOO, and even as much as .500 feet per 

 minute, and no substantial reason can be alleged why such engines 

 should not do good duty ; indeed it may be safely affirmed, that whether 

 the speed of an engine be 100 feet, ioO feet, or 300 feet per minute, 

 it matters nothing; provided all the parts of the engines are well pro- 

 portioned for the pi'oposed speed, the efficient duty and economical 

 use of the engine will be much the same: keejnng this always in 

 mind, that the sloic speed mill be more favourable for the easy and plea- 

 sant working of the engine, and for durability. 



This question may however be asked — Since it is shown that the 

 long stroke has no superiority over a short stroke, but on the contrary 

 that the balance of advantage is rather in favour of the latter, is it in- 

 tended to recommend the invariable adoption of a short stioke engine 

 to the total exclusion of a long stroke '. By no means. All that is 

 contended for is, that in every case a length of stroke should be adopted 

 whether long or short that shall prove to be most convenient, and best 

 adapted to the object for which the engines are to be employed ; and 

 that an engineer should not be fettered and«ramped by any fallacious 

 abstract notions, that what is termed a long stroke engine must neces- 

 sarily be more efficient than an engine with a short stroke ; and that 

 he should not therefore be obliged to sacrifice many other far more 

 important considerations, for the sake of obtaining in every case the 

 longest possible stroke. 



The application of steam power fur the purpose of navigation has 

 had such wonderful results, the character of the steam engine has be- 

 come so greatly changed, and the proportions so altered, that a marine 

 engine of the present day, and a land engine of former times can 

 scarcely be recognised as belonging to the same class of machines. 

 The length of stroke of marine engines is probably not more than half 

 what used formerly to be given to engines of similar power for mining 

 and manufacturing purposes, but still no one can say that this departure 

 from old rules and maxims has been attended with any disadvantage ; 

 on the contrary, it can be shown to have been most beneficial and 



glorious in its results; and if a slill further departure from old estab- 

 lished notions can be proved advantageous for steam navigation, we 

 can have no reason whatever to regret die change. 



There is no question that the ordinary beam engine as employed in 

 steam vessels has proved most efficient, and that in its application it 

 has been productive of vast benefit. If however, by a modification of 

 the existing steam engines, these benefits can be still further augment- 

 ed, and that in an eminent degree, no consideration ought to stand in 

 the way of the proposed improvements. The great and paramount 

 objects to be aimed at in the construction of steam engines for navi- 

 gation are the following, viz., the greatest saving of fuel, the greatest 

 saving of space, the greatest saving of weight, and the greatest dura- 

 bility of the machinery. The more eminently the marine engine shall 

 combine the above important qualities, the more nearly will it have 

 arrived at perfection ; and much as may be advanced in favour of the 

 beam engines generally used for marine purposes, it cannot be con- 

 sidered presumptuous to declare that the system of engines employed 

 in the "Cyclops" and "Gorgon" Fiigates is far superior in all the 

 qualities before enumerated. 



It only remains to be stated, that the real question is, not whether 

 the stroke of an engine shall be 8 feet or 4 feet;' but relates to a dif- 

 ference of stroke, of probably from 7 feet to G feet: that is, whether 

 the reducing of the stroke of a 200 horse engine one fool, with a pro- 

 portionate increase of diameter in the cylinder, can be attended with 

 such injury and inefficiency as shall wholly neutralise or outweigh all* 

 the important advantages of the Gorgon Engines. 



In conclusion, it should be observed that as regards the ordinary 

 beam engines, there are many circumstances of convenience wdiicli 

 render it advisable to make the stroke as long as practicable, i. e., the 

 adopting a tall nan-ow cylinder instead of a short and wide cylinder; 

 for in the arrangement of the ordinary beam engine for marine pur- 

 poses, it is evident that a considerable space lengthways is required 

 for conveniently placing the slide jackets and passages, the condenser, 

 the hot-well, and the air pump ; this necessarily causes a great elonga- 

 tion of the side levers or beams; there is therefore much local con- 

 venience in making the stroke long, and thereby having a tall narrow 

 cylinder instead of a short wide cylinder, less strain is thrown upon 

 the beams ; the beams become more close and compact, and afford 

 more space for a passage between and on the off-sides of the pair of 

 engines: the cross-heads and fork -heads become shorter, and have 

 much less strain thrown upon them ; these are all very important con- 

 siderations which clearly indicate the convenience and possible advan- 

 tage of having as long a stroke as possible in the ordinary beam engine. 

 But in the Gorgon Engine none of these considerations have any in- 

 fluence whatever ; here there are neither beams nor cross heads ; we 

 can increase the diameter of the cylinder to almost any extent without 

 any local inconvenience whatever. 



We shall conclude these observations with the remark, that as it 

 cannot be proved that there is any superiority in a long stroke engine, 

 over a short stroke engine, and as it is also evident that there is no 

 disadvantage whatever in employing a short connecting rod, it is there- 

 fore clear that the two objections are decidedly absurd and ground- 

 less. 



Ok the Friction i.\ Steam Exgink. 



In the preceding pages we have offered an investigation of the com- 

 parative merits of the Gorgon, and of the common beam engine; in 

 the course of our reuiarks it became necessary to advert to the im- 

 portant subject of friction; it will not therefore be deemed misplaced 

 to add a few general remarks upon the nature of the friction, vpliich 

 occurs in a steam engine of the usual construction. 



To attempt anything like a correct estimate of the absolute quantity 

 of friction in an engine, would we conceive be very fallacious, because 

 there are so many circumstances which affect the quantity of friction, 

 which are quite bevond the reach of calculation; as for example, the 

 uncertain degree of tightness to which the several bearings or pack- 

 ing may be screwed down — the state of the rubbing surfaces, as to 

 smoothness, polish or roughness — the perfect or imperfect state of the 

 lubrication, Xrc, all of which are circumstances which have a vast in- 

 fluence on the quantity of friction in a steam engine. From observa- 

 tions which the writer has made he is induced to believe, that in a well 

 made engine, in good working condition, the total amount of friction 

 does not exceed five or six per cent, on the whole power of the engine ; 

 but that with no very great change of circumstances this quantity may 

 be increased readily to as much as 10 or 12 per cent. 



It happens however that in the preceding investigation, the con- 

 sideration of the absolute quantity of friction in the engiue, is not re- 

 quired ; all that is wanted is on estimation of the relative proportions 

 of friction which are due to tL> several parts of the engines; now this 



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