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On the Boilers of Steam Engines, and the Construction of Engine Chimneys

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On the Boilers of Steam Engines, and the Construction of Engine Chimneys Downloaded from http://pygs.lyellcollection.org/ by guest on October 1, 2021 ]3 mighty agents the volcano and the earthquake, upheaved the riven rocks, and brought their treasures to the light of day."—(Loud applause.) The CHAIRMAN eulogised this excellent Paper, and invited discussion, but none took place. MR. HARTOP ON STEAM BOILEBS AND HIGH CHIMNEYS. Mr. HARTOP next made a communication " On the boilers of steam engines and the construction of engine chimneys." He said: Onpresenting myself before a meeting at Leeds, (where the steam-engine is so well understood,) to make observa­ tions on steam en^ne boilers, I feel some apology to be due from me, bat i trust that, however trifling the advants^e panted ooi owjr be, its app)ic»<!i<Hi in so wide a field as is here presented will amply repay any attention given to it. I need not go further back than the introduction of the waggon boiler by the late Mr. Watt, which, from its excel­ lent arrangement, was the standard boiler for so many years* during which time a vety general opinion prevailed amongst practical men that, whenever the length of the boiler exceeded four times that of its grate (say 25 feet), such additional length was useless, as to the quantity of steam produced, although a considerable degree ot heat always passed away up the chimney. The cause of this I conceive to be that the heated air in these flues passes last, and therefore when at its coolest, through the side flues, by which it is brought in contact with the water near the surface in the boiler, and therefore at that point where it was the hottest; in consequence of which ttie boiler, if made very long, might re-impart a portion of its heat to the air in the flues before it passed to the chiomey. This point will, however, be better defined on our consi­ dering the boiler now in general use in Cornwall. Beiore doing BO, I may, however, be excused, for making a few observations on a boiler, which, from its simplicity and strength, is at present becoming a very fashionable one, if I may be allowed tlie expression—I mean the cylindrical boiler with semi-spherical ends. This, there can be no doubt, te a boiler of great strength, and I believe it was introduced St a time when engines were in use with steam at 2001bs. or S60 lbs. pressure per square inch. This dangerous pressure, I am happy to inform the public, is in modem engines not required, the highest now in use being that for locomotive engines at about 60 lbs.per square inch; the boilers for which are so constructed as to render danger to the public very improbable. In the expensive engines of Cornwall, the steam used rarely exceeds SOlbs. per square inch, and in the high pressure enginps of the best makers the steam in use 19 Downloaded from http://pygs.lyellcollection.org/ by guest on October 1, 2021 14 little more than 301bs. per square inch, from which it will be seen that great strength in a boiler is not now so requisite as formerly, and particularly when it is considered that the same accidents will happen to the strongest as well as to the weakest boilers, from similar causes, and that when they happen to a strong one, the explosion is the more terrific in the direct proportion as the boiler is the stronger. We should therefore avoid the cause of these dreadful aoeidenta rather than strengthen the boilers. Now, there is one very great disadvantage in the cyUndrical boilers, viz., that the incrustation will all collect in that portion of the boiler whch is nearest the fire, and being a non-conductor of heat, will expose that portion of the boiler wliich lies between the fire and such incrustation to be burnt away. The argument in favour of this boiler, derived from " the ease with which it may be repaired," is therefore more than done away with by its so often standing in need of that repair which in well constructed boilers will not be required for the first 12 or 14 years. The next and last boiler I shall at present occupy your time in considering, is that of the Cornish boiler. It consists of an outer cylin­ drical case, having an inner tube passing through its whole length, in one end of which the fire bars or grate is placed, by which arrangement the heated air and flame is made to pass nearest the surface of the water in the boiler, where both air and water are the hottest j the former then returns through the side flues, and, descending under the grate, passes under the boiler last, where both the heated air and water are at their coolest, so that in a boiler of sufficient length the whole heat given out by the fuel may, under this arrangement of the flues, be imparted to the water in the boiler, and it is consequently found in Cornwall that they may be used to advantage to the extent oififty feet in length. I am induced to appear before you on this subject in conse­ quence of my not having found these points hinted at either in the very excellent practical work on steam-engine boilers by Mr. Armstrong of Manchester, or elsewhere. I may here also mention the very great importance it is to the owners of steam-engines that the iron selected for these boilers should be of a proper quality for that purpose, for I have known many instances of the bottom of boilers being entirely worn out in 18 months, instead of lasting nearly as many years, the land of boilers in both instances being in every respect the same, firom which circum­ stance there can be no doubt that it is on the real stamina of the iron from which the boilers are made that their goodness or goodfomothingness depends. Con­ nected with this subject is that of the chimney, which is very often carried to the height of 160 and 200 feet, and consequently made so small in the internal flue at the top Downloaded from http://pygs.lyellcollection.org/ by guest on October 1, 2021 16 as to cause the smoke to pass off with some difficulty. Having about 18 years ago built one 110 feet high with its internal flue wider at the top than at the bottom, it was found in practice to answer so well that on applying 14 puddling and other furnaces to it; the draft up to that point seemed rather to be improved with each additional furnace than impeded. I now find the practice becoming a general one in Scotland and Lancashire, which I attribute to my having mentioned the circumstance from time to time to my friends; and I do not hesitate to say that in good situations 80 feet will be found an ample height for the largest engines, and 100 feet in situations less favourable. The CHAIKMAN having invited discussion— Mr. J. G. MABSHALL said the meeting was much indebted to Mr. Hartop for his observations respecting steam boilers. One part of the subject which he had explained he thought exceedingly satisfactory; he alluded to his description of the superiority of the Cornish boiler, over those com­ monly used called the waggon boiler. He himself thought them much superior, and chiefly for the reasons that Mr. Hartop had stated—their greater adaptation to the applica­ tion of heat. He had been so far convinced of that that he had caused to be erected boilers of that shape ; but there was one point which Mr. Hartop had reckoned amongst the advantages of the Cornish boiler that he should be rather disposed to doubt, and that was its greater safety. The external shape of that boiler was undoubtedly stronger, but he thought that the internal surface, which had to resist the fire, was weaker, by reason of its form, than the ordinary boiler; and he believed that several steam-boat accidents had been attributed to the internal shape of the boiler. Its con­ struction was such that if the internal tube in any degree got out of its correct shape it immediately collapsed. Several acci­ dents had oecurted to the Cornish boiler,and he thought it was most probably to be attributed to that source. He thought it would be desirable as a means of guarding against acci­ dents, that the makers of those engines should state the force they would bear externally and internally ; and it might atso be of advantage if means were devised for " staying" them. With respect to what Mr. Hartop had said about the inutility of extending the length of the boiler, he should be disposed to differ from him, inasmuch as the parts which received the application of the fire were extended, as well as those that did not receive it. With respect to the per­ formances of the Cornish boilers he also thought that there was still a great deal of doubt. The results of experiments upon different boilers varied materially, and he thought it very possible that they might have been incorrectly taken. Downloaded from http://pygs.lyellcollection.org/ by guest on October 1, 2021 16 They were all high pressure engines, and some portion of the variance might have arisen from leakages, &c. He did not think that the saving in the Cornish engine was wholly to be attributed to the construction of the boiler. Upon the whole, he thought that the sugges­ tion to adopt the Cornish boiler was a very valuable one, for it was equally adapted to high and low pressure engines, care being taken as to the relative strength of the internal and external surfaces.
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