316 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fOcTOBEB, 



tricts; and although the Cornish miner set an excellent example 

 and exhibited a saving of more than one-half the fuel, there were 

 nevertheless few if any attempts made to reduce what is now con- 

 sidered an extravagant expenditure in most if not the whole of 

 our manufactories. But in fact the subject was never brought 

 fairly home to the millowners and steam navigation companies, 

 until an equalization or reduction of profits directed attention to 

 the saving attainable by a different system of operation. 



Ten years ago the average or mean expenditure of coal per in- 

 dicated horse-power was computed at from 8 to 10 lb. per horse- 

 power per hour, but now it is under 5 lb. per horse-power per 

 hour in engines that are worked expansively, and even then they 

 are far below the duty of a well-regulated Cornish engine, which 

 averages from 2j to 5 lb. per horse-power per hour. 



This difference in the consumption of coal may be attributed to 

 two causes; first, the conditions under which the duty of the two 

 engines (that of the Cornish miner and tlie manufacturer) are 

 respectively performed. The first being chiefly employed in 

 pumping water, has the benefit of alternate action in overcoming 

 the inertia of a large mass of matter, which when once in motion 

 is easier continued, for a definite time, than a continuous power of 

 resistance, such as exhibited in corn and cotton mills. Another 

 cause is the greater care and attention which the Cornish man 

 pays to his boilers, steam-pipes, &c.; they are never left exposed, 

 but are carefully wrapped up in warm jackets and well clothed, to 

 prevent the escape of heat. Even at the present day, it is lament- 

 able to see (in the coal and iron districts) the great and extrava- 

 gant waste that is continually going on, for want of a little con- 

 siderate attention in this respect: the only excuse is the cheapness 

 of the fuel — but that is not an excuse, for if one-half can be saved, 

 and coal could be got at 1*. per ton, it is certainly desirable to 

 save sixpence out of the shilling, when that can be accomplished 

 at a trifling expense. But one of the chief, if not one of the most 

 important reasons for the exercise of economy in fuel, is the re- 

 duction of profits on articles manufactured by power; under these 

 circumstance, a saving in coal becomes a consideration of some 

 importance, and to these reductions alone may be traced the 

 powerful stimulus which of late years has been prevalent in that 

 direction. The low rate of profit in manufacturing operations, 

 and a desire to economise and reduce the cost of production to a 

 minimum, has been of great value in its tendency to improvement 

 in the economy and efficient use of fuel, and also to the use of 

 high-pressure steam and its expansive action when applied to the 

 steam-engine. In France and most other parts of the continent 

 this system has been long in use, and although its effects as well as 

 its economy have been long known in this country, it was only 

 within the last few years that the benefits arising from it were ap- 

 preciated. For a great number of years a strong prejudice existed 

 against the use of high-pressure steam, and it required more than 

 ordinary care in effecting the changes which have been introduced: 

 it had to be done cautiously, almost insidiously, before it could be 

 introduced. The author of this paper believes he was amongst 

 the first in the manufacturing districts who pointed out the ad- 

 vantages of high-pressure steam, when worked expansively,* and 

 for many years he had to contend with the fears and the pi'ejudices 

 of the manufacturers, before the present system of economical 

 working was adopted. 



The first attempt was by improvement in the construction of 

 boiIers,t and subsequently in the valves of the steam-engine, 

 adapted to either low or high pressure steam when worked expan- 

 sively; the latter of which it is the principal object of the present 

 paper to develope. 



The expansive action of steam has been variously estimated by 

 different writers, but all seem to agree in opinion that a consider- 

 able saving is effected by that process. It therefore becomes a 

 question of importance in a connnunity whose very existence 

 almost depends upon the steam-engine, how to work it advan- 

 tageously and at the least possible cost. The great variety of 

 schemes and forms which have been adopted for the attainment of 

 these objects have been exceedingly various, ingenious, and inter- 

 esting; and the investigation of tlie different theories aiul applica- 

 tions that have been submitted for public ajiproval, would form an 

 exceedingly attractive if not a useful history of the various dis- 

 coveries to which we are in a great measure indebted for the 

 present improved construction of the steam-engine. 



The elastic force and expansive action of steam were well known 

 to Mr. Watt, and some of his immediate contemporaries and suc- 

 cessors, such as Smeaton, Cartwright, Woolf, Trevithick, and 



* .^ee Paper rend before the Geuiogiciil Society of Manchester in the year 18-10, on the 

 EL'unomy uf Fuel. 



t See Report on the Prevention of Smolie ani Economy of Fuel. — TraLsactions of the 

 British Association, IH-U. 



others: but the fears entertained of explosion at that early period, 

 and the difficulty of constructing vessels strong enough to contain 

 high-pressure steam, were probably the greatest drawbacks to its 

 introduction. Woolf and Trevithick were probably among the 

 first to grapple with this dangerous element; and the former, in 

 order to economise fuel, introduced the double-cylinder engine, 

 whereby a great saving was effected by increasing the pressure of 

 steam in the boiler, and allowing it to pass from one cylinder to 

 another of three or four times the capacity, by which its volume 

 was expanded, and by these means a saving was effected and an 

 extra duty performed. If, for example, taking a double-cylinder 

 engine, the high-pressure cylinder being one-fourth of the capacity 

 of the cylinder from which the steam is condensed, there will be for 

 one cylinder full of steam an expansion of four times its volume, 

 — this of course with a diminished pressure in the ratio of tlie 

 capacities of the two cylinders. Comparing this with a similar 

 process in a single cylinder equal in capacity to the two cylinders, 

 and fitted with a well-constructed apparatus, regulated so that 

 only one-fifth of the contents of the cylinder (equal in capacity 

 to the small cylinder on Woolf's plan) is filled with steam of equal 

 density, and the remaining four-fifths (equal in capacity to the 

 larger cylinder) is allowed for expansion, it is evident that the 

 communication being thus suddenly cut off from the boiler after 

 the piston has been urged through only one-fifth of the length of 

 the stroke, the expansive force is then used in completing the re- 

 maining four- fifths of the stroke, and the result must be nearly 

 the same as that obtained with the two cylinders on Woolf's plan. 

 The advocates of Woolf's system, however, insist upon its su- 

 periority, not from the actual force given out (which is rather in 

 favour of the single cylinder than the double, in consequence of 

 increased condensation in the steam-passage between the two 

 cylinders), but from the superior action and greater regularity of 

 motion which in the former case is produced. To some extent this 

 is the case, but not to any appreciable amount provided the fly- 

 wheel is well-proportioned to the pressure and power at which the 

 engine is worked. In the double engines which are now in com- 

 mon use, that is, when two single engines are coupled together 

 with the cranks at right angles to one another, there is less 

 occasion for a heavy fly-wheel, as the effect of a large expansion is 

 less felt, if not effectually neutralised. The results, therefore, of 

 the double-cylinder engine and the single engine working at equal 

 rates of expansion, are virtually the same as regards power and 

 economy of fuel, if the comparison be not in favour of the single 

 engine. 



Having come to the conclusion that the same duty can be per- 

 formed by the single as by the compound engine, and considering 

 the important advantage of simplicity in mechanical construction, 

 in opposition to complexity however ingeniously contrived, it 

 becomes a question how to obtain an effective as well as a simple 

 process for the attainment of that object. 



The first attempt was by revolving tappets, which had been long 

 in use; these being formed and regulated in such a manner as to 

 cut oft' the steam at such a point of the stroke, as to give the exact 

 quantity of expansion required. These tappets, to say tlie least, 

 were from various reasons objectionable, as the weight of the 

 vertical rods and slowness of motion prevented them from produc- 

 ing the desired effed^. The steam valves could however be fixed 

 so as to cut off the steaiH at the required point of the piston- 

 passage in the cylinder, but the motion is not effected with the 

 velocity essential to an eflScient process of expansive action. 

 Other processes have been tried for working steam-engines expan- 

 sively besides those already noticed; amongst them may be noticed 

 the equilibrium valve, worked by double cams from the crank- 

 shaft. This method is generally used and adapted to the marine 

 and old engines, but its application is seldom of much value unless 

 the engines and boilers are capable of bearing a pressure of 15 lb. 

 to 20 lb. on the square inch. 



Another fault to which this description of valves is subject is 

 their distance from the steam-ports into the cylinder, and the large 

 quantity of steam which occupies the space between the cut-off 

 valve and tlie working cylinder of the engine. To remedy these 

 defects, and to apfily a better system of expansion to the common 

 coiulensing engines, the following apparatus and mode of working 

 the valves was introduced. 



In giving a description of this effective and simple apparatus, it 

 is but fair to state that the first idea of this invention was sug- 

 gested by Robert Biownhill, — at first imperfectly constructed, but 

 since greatly modified and perfected by the author of the present 

 paper. 



Tlie annexed engraving represents a section of the valves. It 

 will be observed that the cylinder A, the steam-chests C, D, and 



