SOME EXPERIENCES AND RESULTS DERIVED FROM THE USE OF HIGHLY SUPERHEATED STEAM IN ENGINES. - BY NR.R. LENKE,- OF ERITH. In no branch of heat-engine building has such an amount of study been spent as in steam-engines, from Watt’s time up to to-day. The economy of the steam-engine is, in spite of all efforts, not the best, and the steam-engine in its highest perfection attainable at present cannot claim the first place in comparison with other heat-engines. And so the problem of generating and using superheated steam has become a question, from the solution of which a considerable stride in improving economy has been expected and really made. Superheated steam is generated by the addition of heat to saturated steam. The behaviour of superheated steam is similar to that of gases ; it is a very bad conductor of heat, and has the special peculiarity of being able to lose a certain amount of heat without becoming saturated or wet steam. The thermal capacity of steam is only 0-48,therefore very little heat is required to superheat steam ; but as the steam loses the heat as quickly as it acquires it, every passage conveying superheated steam must be well covered with non-conducting material. Although there are some losses when using superheated steam on account of the heat radiation, they are very much smaller, because the loss of heat from superheated steam has lowor calorific value than the latent heat of saturated steam. Superheated steam has a greater volume per unit of weight tliau saturated steam at the game pressure, hence one advantage, and the 3 1%

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higher the temperature, the greater this advantage. At various pressures and temperatures the increase of volume may be taken from the following Table 1:- TABLE 1.

Pressure. 390' F. 570' F. 750' F. ------70 1.1 1.33 1.57 ------115 1.06 1.29 1.52 ----~----~- 170 1.02 1.24 1.46

~~

Table 1 shows that the higher the pressuro is, the smaller the increase of volume; and it is proved from practice that the advantage with lower pressure is indeed greater in proportion than with higher pressures. The question may arise whether the increase of volume does not require more additional heat than the benefit derived from it is worth. To show this clearly Table 2 has been prepared expressing how many B.T.U. less are required to produce 1 cubic foot of superheated steam than of saturated steam at the same pressure. For various pressures and temperatures the total heat per cubic foot is as follows :-

TABLE 2.

Pressure. Saturated. 390' F. 570' F. 750° F. ___-_----______70 233 219 192 173 --- 115 350 337 297 267 -~-~--~--___- __-____ 170 492 485 432 398

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 SEP. 1901. SUPERHEATED STEAM IN ENGINES. 849 that is, to produce, for example, 1 cubic foot of steam at 115 Ibs. pressure and a temperature of 670" F., 350 - 297 - 15 kuAcent., .350 less heat is required than to produce 1 cubic foot of saturated steam at the same pressure. With saturated steam engines, 20 per cent. to 25 per cent. of admitted steam is condensed during the admission period, consequently the practical steam consumption is very much in excess of the theoretical. Superheated steam does not condense during this period if sufficiently superheated, hence another advantage. The economy effected by using superheated steam in engines is very remarkable, and, acknowledging this fact, a great number of steam users all over the world superheat the steam, although in many cases only a few degrees, yet a considerable saving in steam and coal is always the result. To obtain the full benefit, the required temperature of steam is 660" to 700" F., and tcr stand this temperature, the engines must be specially designed. It is not sufficient to use mineral oil with a very high flash point, and anyone who tries to supply an existing engine of any kind with steam at that temperature will have a very unpleasant experience, even when using the abova-mentioned oil. The introduction of superheated steam into engines largely influences the expansion of the heated parts. Engines always gave great trouble when the distribution of metal in the cylinders was not uniform, as parts with more metal expanded most, and forced the cylinder walls towards the inside and made the cylinder out of shape. When using liners in the cylinders, they were squeezed in at the ends, decreasing the diameter, and jamming the piston body if sufficient clearance was not provided. With steam-jackets heated with steam of 500" F., the lubrication ceased as the cylinder walls became too much heated, consequently it was found necessary to do away with jackets, or if jackets were already provided, not to pass steam through them. Pistons constructed on the Ramsbottom type always worked satisfactorily, except in the case of pistons fitted with steel springs, when they mere in contact with highly superheated steam. 3M2

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Any kind of gun-metal gets brittle after a very short time, therefore valves, seats, and all parts in direct contact with superheated steam, must be made of cast-iron or other suitable mixture. Copper also loses about 40 per cent. of its strengtli at that temperature, consequently copper bends in pipes are not practicable. The best material for piping has proved to be wrought iron and steel, each pipe being as long as possible, to have the least number of flange&. For long, straight pipe connections, provision must be made to meet the expansion, which is, at 700" F.,0.0037 of the length, so that, for example, 100 feet of pipe extends 0.37 of a foot, or nearly 44 inches. Glands and stuffing-boxes at first frightened users, so the engines were constructed single-acting to avoid the use of glands, but no serious difficulties have arisen on that account. It is advisable to place the stuffing-box as far as possible from the cylinder- end to keep it well away from the hottest parts, and to allow of as much radiation as possible. Sufficient clearance in the neck bush &odd be made to allow for the expansion of piston-rod, and no metal with a melting temperature below that of the steam should be used. Valves and valve gears are influenced in the same way by superheated steam. Valves containing many ribs or different thicknesses of metal (in section), such as plain slide-valves or Corliss valves of the usual construction, are not suitable for high temperatures. A Corliss valve of medium size will stand 480" to 500" F., but no more, and the latter temperature very seldom. The smaller the plain slide-valves are, the higher temperature they will stand : large slide-valves will hardly stand even slightly superheated stearn, if no provision is made for forced lubrication of the valve face. Piston-valves have proved to be most suitable for the highest temperature, owing to their uniform distribution of metal, but even with this sort of valve certain experience is necessary to get them in good working order. With ground valves, the ribs holding the boss for the valve spindle must not begin within the working surface of the valve, but have to be placed beyond that, because they expand and make the valve polygonal. The valves must be ground in other liners to those in which they are to work in the engine ; the former liners have to be smaller in diameter to secure more clewance to

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 SEI’. 1301. SUPERHEATED STEAM 1N ENGINES. 851 provide for the expansion of the valves. The cylinder expands in length more or less than the steam-chest, causing thereby deformation of the latter, which must be carefully considered in design. It is best to work the valves in liners fixed in the cylinder and with a small clearance, sufficient to allow for the dcformation of the steam-chest. With this construction it is of course necessary to make steam-tight joints between the several ports, and this is best done by stepping the liners and seats and using narrow asbestos rings for each step. The liner is then forced on to the small seats by set screws in the cover, these asbestos rings making a lasting joint. Long valves cast in one piece become scored, whether they are cooled from inside with exhaust steam or not ;consequently all valves should be made as short as possible. Rings and springs in valves cannot be recommended, as the steam comes behind the rings and increases the pressure, causing friction and therefore increased oil consumption. As it iti impossible to rely on tightness of piston valves, they must be made as small in diameter as possible. It may be stated here that superheated steam can travel at 30 to 40 per cent. higher speed through steam ports than saturatcd steam, and this fact has to be considered during construction. Two piston-valves working one in the other, as the Rider or Neyer valves, are impracticable for superheated steam. If engines OP that type are intended to be worked with superheated steam, each valve must work in a separate chamber. Double-beat valves can also be recommended as being safe, but fhey require a special arrangement, which is not always obtainable with every gear. Very often it happens when warming up the engines that the valve spindles get hotter than the gland-boxes, and on starting the engine, the friction between spindle and stuffing-box is greater than the power of the spring, and if the valves are not positively driven, they remain open during the full stroke. An engine constructed in accordance with the principles just explained is as safe with superheated steam as any other engine with saturated steam. From the experience over several years, it is not necessary to be bound to single-acting engines. Besides the economy, the use of highly superheated steam has some other advantages which are also important. It makes the steam

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 852 BUPEBHEATED STEAM IN ENGINES. SKI,. 1901. consumption nearly independent of the size of engine, as a small engine has about the same steam consumption as a large one, as for example : an 80 H.P. compound condensing engine uses 10.45 lbs. of steam at 160 lbs. pressure, and a 1,000 H.P. engine uses 9 lbs. of steam per I.H.P. per hour. The use of highly superheated steam does not require high boiler-pressures, 160 lbs. is the highest to be recommended, as no advantage can be derived by exceeding this. As the amount of heat transmitted from the steam to cylinder walls, and vice versa, is much lower with superheated steam than with saturated steam, the whole range of temperature from boiler pressure to vacuum can take place in one or two cylinders, so that the use of a triple-expansion engine does not make the slightest improvement in economy. It is not intended to be understood that the author proposes to do away with all triple-expansion engines ; for very large plants, their use will be necessary for constructive reasons. With regard to economy obtained from engines working with superheated steam, the gain is derived from the larger volume of the steam and the doing away with initial condensation. Generally the steam consumption of modern engines working under good conditions may be taken as follows :- Single-cylinder condensing engines with saturated steam and a pressure of 90 to 100 lbs. per square inch use 19 to 25 lbs. of steam per I.H.P. per hour, corresponding with 373 to 490 B.T.U. per minute. The great difference in temperature between admission and exhaust steam causes much waste by initial condensation, and consequently this type of engine especially favours the use of superheated steam. With superheated steam the consumption has been lowered to 133to 15 lbs., corresponding with 290 to 335 B.T.U. Non-condensing single-cylinder engines gave consumptions of 15 to 18 lbs. of steam per I.H.P. per hour, which is about the same consumption as an average compound condensing engine with saturated steam. The non-condensing compound engine decrease6 the consumption to 14to 16 lbs. per I.H.P. per hour. The compound condensing engine is the most economical, and the economy obtained can hardly be reached by a quadruple-expansion engine working at a pressure of 300 lbs. The steam consumption of

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 SEP.iDO1. SUPERHEATED STEAM IN ENGINES. 863 such an engine either compound or tandem, at 140 lbs. pressure only, never exceeds 10 lbs. per I.H.P. per hour and usually remains below, many tests having proved 8.5 and 8.8 lbs. consumption per I.H.P. To utiljse bettor these temperatures and to work with various loads with safety and nearly uniform economy, Nr. Schmidt has introduced the receivcr-heater with automatic valve. The idea is to keep a steady mean temperature of cylinder walls not higher than will make the lubrication unreliable for different rates of expansion. A few words may be said with regard to the cost of a superheated plant. Superheated steam engines use on an average 30 to 40 per cent. less steam than saturated steam engines of the same type. Consequently boilers can be made 30 per cent. smaller, and the difference in price will nearly cover the cost of the superheater. For the same steam consumption the superheated steam engine is cheaper, as it may be worked with a lower boiler pressure, and it is simpler, i.e., instead of a compound engine with saturated steam, D single cylinder engine with superheated steam may be used, giving the same or better results than the former. With regard to oil consumption, it was found not to be more than that of an ordinary saturated steam engine. For example: a 120 I.H.P. engine used 4 lbs. of oil in 24 hours, and a 300 I.H.P. Corliss compound cngine 2 2 lbs. in 10 hours for both cylinders. In vicw of the great advantages of steam superheating, and the great number of engines running at present satisfactorily, it is astonishing that a few failures have caused prejudices amongst some ungineers, who make the gencral introduction of the use of superheated fiteam very difficult. It will be worth mentioning that the results of' a great number of trials have always proved a great saving in steam and coal, and even with small plants and simple piston-valve engines, almost the samc g[)od economy is obtainable as with large engines with most exact valve-gears. It is therefore recommended that superheated steam should be used in connection with all engines ; the only question to be settled is the degree of superheat, which largely depends ou local circumstances and the construction of tho engine, and this matter should be left to the judgment of an experienced engincer.

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Discussion. The CHAIRMANthought the use of superheated steam had a very great future before it, and they were indebted to Mr. Lenke for having brought before them in a very interesting Paper a number of practical points to which it would be necessary to attend, if they were to make the use of superheated steam successful. Before commencing the discussion, he would ask them to accord a hearty vote of thanks to Mr. Lenke for his Paper.

Mr. BI~YANDONKIN, Vice-chairman, was rather disappointed to find in this excellent Paper no mention of the name or quality of the oil used for lubrication. That was an important point. One would like to know the best oils to me, and the quantity required. Some oils gave good, others bad results. He presumed that the results of the experiments given were chiefly continental. On page 849 there was rather a startling statement, namely, that with saturated steam 20 to 25 per cent. of the admitted steam was condensed during the admission period. That might be so in single-cylinder non-jacketed engines, but in a thoroughly well jacketed cylinder he doubted whether it would be so much. From many continental tests with the very best triple 1,000 H.P. engines with dry or highly superheated steam, little economy was found due to superheating. He was a strong advocate of superheated steam, and was pleased to see so many good experiments recorded.

Mr. C. C. LEACHsaid the experiments were comparisons of the very best economical engines, but nearly all pit engines were most wasteful and too large for the work they had to do. In nearly all cases they had to slow down and work with varying loads ; minding engines ran 20 seconds and stopped 5 or 6 seconds. Would superheat get a greater gain of economy with a bad engine than with one of these high-class engines ?

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Mr. HENRYLEA said he would like to ask one question. Supposing that one had a really well-made compound engine working with saturated steam, the stuffing-boxes and piston rings being constructed in the usual manner, what superheat temperature would it be safe to employ with such an engine, using the special oil which Mr. Lenke has found necessary? To alter the engine to conform with the conditions laid down in this Paper would seem to be impossible. It would mean throwing the engine away, and putting down a new one built on Mr. Lenke's lines.

Mr. J. HARTLBY\~7~~~s~~~~, Vice-chairman, said that about eight months ago he had introduced a superheater at the works of his firm, Messrs. Joshua Buckton and Co., Leeds. Their Lancashire boiler was 8 feet 6 inches diameter and 30 feet long, the furnace flues were 3 feet 6 inches diameter, and steam was raised up to 100 lbs. pressure. The superheater consisted of long U-shaped tubes, which hung down from a cast-iron box with a division, so that the steam passed down the side of the U furthest from the flame and came up the sides of the U closest to the flame. The gases impinged upon these bent pipes right opposite the furnace flues, and before they went round the sides and bottom of the boiler to escape up the chimncy. They distributed about half their power to distances of 150 feet from the central boiler, and the other half of the power they took as ncar the boiler as possible. The engines were of different types, some of them had ordinary slide-valves, some of them had double-beat trip-valves for letting in the steam, and Corliss valves for the exhaust, and some of them were steam-hammers, with piston-valves of some sort. They had not had thc slightest difficulty, and there had been less trouble with cylinder-covers and pipe-joints. All the engines had run more cheerfully, their shafting made more revolutions per hour, and maintained its speed better with extra loads. The pressure was 100 lbs., and the temperature therefore with saturated steam would be about 340" P.; he thought the temperature they got from the superheater, which was superheating the IThole of the steam that was used out of the boiler, WES about 500" F. The consequence was they were getting only 160" of

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 856 SUPERHEATED STEAM IN ENQINES. SEP. Inol. (Mi-. J. Hartley Wickstced.) superheat. He supposed that was the reason they had had no trouble, but they were satisfied that they had a great deal of benefit.

Mr. MICHAELLONGRIDGE said that the prevention of cylinder condensation considered in the Papcr was not the only and, perhaps for the North of England whero coal mas cheap, not the most promising application of superhcating. Superheated steam could also be used in some cases with great advantage to heat and evaporate water. In this connection the name of McPhail, of Wakefield, should be mentioned, not only because he had shown how the output of a boiler could be largely increased without materially increasing the space occupied or watering the steam, but because he had shown engineers how to make a simple and durable superheater which had served as the prototype of the majority of the superheaters now in use in England. Superheating was also useful as a steam dryer only. In works where there were long steam-pipes leading to scattered engines, a considerable mving could be made by supplying the engines with steam instead of water and steam, and this advantage could be gained by a very moderate degree of superheat. This entire prevention of cylinder condensation required a higher degree of superheat than could be safely used, except in specially constructed engines, but initial condensation might be materially reduced, and possibly in some cases entirely prevented, by Superheating to less than 500" F., a temperature which the Corliss valvcs in general use seemed to be capable of standing. With a superheat of 100' to 120" F., he thought there would be a saving of 10 to 12 per cent. in the case of a good mill engine.

Professor WILLIAMRIPPER thought the point most engineers wanted to hear about was the extent to which they could safely usc superheated steam. He must confess that, if ho were a manufacturer already fitted up with good plant, he would feel great hesitation in introducing superheating, after reading the Paper, which drew attention to the many mechanical difficulties involved in the use of high superheat. But it must be noted that the difficulties applied to high superheat only, and the practical point was to what extent was

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 SEP. 1901. SUPERHEATED STEhH IN ENGINES. 857 it applicable to ordinary plant such as Mr. Wicksteed had been describing. He thought one reason why he bad no difficulty with superheating mas that his apparatus was to some extent similar in its action to the McPhail apparatus, that was to say, the McPhail apparatus was an arrangement by which highly superheated steam before passing to the engines was compelled to pass through water, and the superheater became a kind of steam generator.

Mr. WICKSTEEDsaid his apparatus was not like that.

Professor RIPPER continuing, said Mr. Wicksteed allowed the steam to pass through 3 long series of pipes in the cold air, which had the same cooling effect on the stcam. If the steam were of a very high temperature, the chances were that it was 50" (ir 100" less hot when it reached the engines or steam-hammers ; and the result was that they were dealing with low superheated steam, and were not getting the mechanical difficulties that were suggested in the Paper, whilst they were getting the advantages that arose from evaporating the water in the steam-pipes and prevcnting condensation. There had been quite enough practical experience in this country with low superheating to shorn that, in an ordinary plant with the appliances just as they mere, superheat amounting to 100" to 150" could be quite safely and wisely used, and would work with a considerable economy. If the phenomenal rcsults which were there tabulated had to be expectcd or attained, it would only be possible to attain them by having an engine specially constructed, in order to avoid the mechanical difficulties which arose from high superheating.

Professor JOHNGOODMAN said it would be interesting to know how much Mr. Wicksteed saved on his coal bill by superheating. His own experience showed 10 per cent. saving for 50 per cent. of superheat. He moulcl like to ask Mr. Lenke what mixture of cast-iron he found best .for cylinders working with a high degree of superheat.

Mr. E. HALL-BROWNsaid Mr. Lenke's experience in the use of highly superheated steam made his Paper as valuable as it was

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 858 SUPEBHEATED STEAM IN ENGINEB. SEP. 1901. (Mr. E. Hall-Brown.) interesting. As a marine engineer he was anxious to know how far they would be justified in adapting their engineslfor the we of highly superheated steam. His object in rising therefore was to obtain further information. Mr. Lenke stated (page 847) that “although there are some losses when using superheated steam on acconnt of the heat radiation, they are much smaller because the loss of heat from superheated steam has lower calorific value than the latent heat of saturated steam.” He would like this more fully explained. Again, Mr. Lenke stated (page 849) that to obtain the full benefit, the required temperature of steam was 660” to 700” F. Why stop there ? He presumed it was because the mechanical difficulties then became insuperable. Mr. Lenke referred (page 853) to the cost of a superheated plant, and stated that the reduction allowable in the size of the boilers would cover the cost of the superheater. But what about the engine? He presumed this was also more costly than an engine designed for using saturated steam. It would be interesting to have some figures respecting this point. In regard to internal lubrication, as many marine engines were run without the use of any cylinder oil, it would seem that more oil must alwajs be used with engines using highly superheated steam.

Professor W. H. WATKINSONsaid that Mr. Lenke’s communication was one of great value, and he wished to congratulate him on having compressed so much useful information into so short a Paper. The author, in stating some of the reasons for the great reduction in steam consumption due to superheating, had omitted what was, he believed, one of the principal reasons, namely, the enormous reduction in the leakage past valves and pistons which was effected by the use of superheated steam. As to the use of special lubricating oil, he had, on one occasion, some difficulty with a Corliss engine of 1,250 I.H.P., and oil at 5s. per gallon was tried instead of the oil at 2s. 6d. per gallon which had been used prior to the adoption of superheating. At the same

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 SEP. 1901. SUPERHEATED STEAM IN ENOINES. 859 time slight alterations were made in the engine. When the first barrel of the higher priced oil was finished, the cheaper oil W~S again tried, and it had been used ever since without the slightest trouble.

Mr. LENKE,in reply, said he must thank them for the kind remarks that had beenmade about his Paper. He would do his best to reply to these various questions as far as time permitted. In regard to the quality of oil used for engines of the type referred to, he found one made by the Petroleum Raffinerie, KorE, Bremen, to be very suitable, and lately had procured a sample of a new oil made by Snowden, Sons and Co., Wllwall, which gave very good results. Exhaustive trials with this oil had not yet been made; so that he was unable to give any definite figures. The price was about 28. 6d. a gallon. The tests referred to were made on continental engines, as there were at present only a few small engines running in Great Britain ; but in a few months he would be able to publish similar results from engines made and at work in this country. With regard to his figures of 20 to 25 per cent. loss through initial condensation, he had taken this as an average from a great number of trials, though there were engines losing nearly 40 per cent. of steam by condensation. The question as to whether any benefit might be derived from superheating with highly economical saturated steam-engines was best answered by reference to some trials carried out by Professor Schroter on a triple- expansion engine. The engine used 12 lbs. of saturated steam per I.H.P. per hour, a very low steam consumption indeed, but with steam superheated to 500" F. only the steam and coal consumption was reduced 18 per cent. To what degree steam had to be superheated to suit an existing engine should be left to an experienced engineer. No general rule could be given, but in any case a saving in coal was effected by drying the steam, and the farther the engines were from the boiler the greater the saving. For hauling and winding engines superheated steam hat! also effected a great saving, and for this type of engine the temperature should be a few degrees below the highest temperature so as to allow a

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 860 &UPEREEATED 5TEAM IN ENGINEB. SEP. 1901. (Mr. Lenke.) certain rise whilst the engine was standing. 660" to. 700" F. had proved to be the highest temperatures which were both well undcr control and safe for superheater and engine. Beyond that, superheater coils began to anneal and became permeable. As this Paper was dealing with steam in engines, no names of superheater makers could be mentioned. The metal used for cylinders should be hard, close-grained cast-iron. A question had been raised as to the cost of superheated steam-engines. One essential condition in their construction was simplicity, as would be seen by reference to that part of the Paper dealing with the details of construction. From this it followed that the cost would not be more, but usually less, than for economies1 saturated steam-engines. Concerning the amount of leakage for valves for saturated and superheated steam, he was inclined to believe that under the same condition the leakage of superheated steam wm less than that of saturated steam, but at the present time it was not yet satisfactorily solved. As a matter of fact the same piston-valve leaked less with superheated steam, but this was due to the greater expansion of the valve, as those valves which xere tight with superheated steam leaked with saturated steam. With valves equally tight under both conditions the leakage was, as he had said, not yet determined.

Communications. Mr. D. a. TODDwrote that during the discussion which followed Mr. Lenke's Paper the question of the limit of temperature of superheated steam was raised, and as the writer had had a somewhat unusual experience in this connection, the following notes might be of interest. About two years ago he had to do with several large boiler plants in the neighbourhood of Glasgow, which supplied steam to s number of high-speed engines made by some of the best-known English makers. The boilers were fitted with superheaters. These superheaters were of a type which has been adopted by several manufacturers, namely, a series of small tubes bent in the form 01 a U, and fixed at their ends to collecting boxes, into one of which

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 Stil.. 1901. SUPERHEATED SrEAN IN ENOINEB. 861 the steam from the boilers was passed, and the exit steam taken off the other. The tubes themselves were exposed to the furnace gases, and the trouble experienced in the case in question, where the boiler was of water-tube type, was repeated in other cases with Zancashire and other boilers. Owing to several causes, which it was unnecessary to refer to, the tcmperature of the superheated steam reached, and sometimes even exceeded, 1,000" F. To produce this condition the tubes and boxes were exposed to such @ high tcmpernture that they had apparently become red-hot, and an nlarming state of affairs ensued. Trouble was first of all experienced with the engines, in which the metallic packings of the piston-rod and valve-spindles gave out, and the cylinders showed such signs of over-heating that the engine-makers intimated that unless steps were taken to regulate the amount of superheat so that it should not exceed 50" to 60°, they would decline all further responsibility. The superheaters themselves also gave evidence of being in a dangerous condition ; while they were at work one could hear steam escaping into the flues, and by opening an inspection-door, which had been arranged for the purpose, it was apparent that the tubes had been distorted, and were showing signs of great distress. The writer thereupon instructed the workmen who had charge of the erection to have the boilers laid off at the following week-end, and on the Sunday morning he made a personal examination of the superheaters. The tubes were found to be badly distorted, and in nearly every instance the expanding bad given way ; the tubes were quite loose in their seats, the blade of a penknife could be just passed between the tubes and the connecting-box, and they were apparently only prevented from being blown out of their seats by the excessive amount of belling or beading-over which the tube ends had received after the expanding was completed. The boxes were also slightly distorted, but the most remarkable feature was, that in the tubes, vhich before being fixed in position had been carefully cleaned out, there mere a large number of pellets like small marbles, composed apparently of oxide of iron. It was evident from this that, at the 1,000" F. temperature which the thermometer showed, the steam, or at least a portion of it, had reached the point of dissociation, and the

Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 862 SUPERHEATED STkAY IN ENGINES. SEP. 1901. oxygen had attacked the tubes, probably the heated condition of the latter favouring the process of chemical combination. No other explanation could account for the presence of those pellets. If, then, as this phenomenon seemed to indicate, the point of dissociation of steam commenced somewhere about 1,000" I?., this would fix the limit to which superheating could be carried, unless the superheaters themselves and the walls of the cylinders, valves, &c., with which the steam came in contact, were made of material not subject to oxidization.

Messrs. HICK,HABGREAVES and Co., of Bolton, wrote that their experience did not bear out the statement in Nr. Lenke's Paper as to Corliss valves giving trouble above 450" or, at most, 500" F. They had for more than six years past been supplying superheaters in large and increasing numbers-some hundreds in all-a large proportion being for use in connection with their standard Corliss engines, which were mostly of considerable size; the largest at present working with superheated steam were a set of horizontal cross compounds, giving 2,300 I.H.P., the cylinders being 31 inches and 64 inches, with Corliss valves, stroke 6 feet, revolutions 55, boiler pressure 160" F. The temperature of the superheated steam had reached in one case 750" F. at the superheaters, and in another 700" I?. at the engines, which in this case were of 1,000 I.H.P. of the vertical type, also with Corliss valves ; but 500" to 550" F. was more usual. In no single instance, out of the large number of their Corliss engines in use with superheated steam had trouble of any description been noticed or reported in connection with the Corliss valves ; and in only one instance had trouble been reported with the piston rings, which could fairly be ascribed to superheating, They bad in fact been most agreeably surprised at the entire absence of any serious difficulties in connection with superheating, and they were secommending and supplying superheaters as a matter of routine, and quite beyond the experimental stag, with the majority of the engines and boilers they made. The results had, on the whole, been very gratifying, economies up to 30 per cent. having been reported, with simple engines working at 60 lbs., and over

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23 per cent. with triple expansion engines at 200 lbs., whilst a compound engine with steam at 175 lbs. pressure superheated only 76” F. had given one I.H.P. for 11.1 Ibs. of gross feed-water. Mr. C. H. MOBERLPwrote that the author stated the case of superheated steam very clearly in its present stage of development. It was interesting to follow this development in Germany, where it has been extensively and successfully adopted in mills and factories, as has been shown by numerous articles in the “Zeitschrift des Vereines deutscher Ingenieure,” namely :- In 1894, page 737, a gcneral description of the Schmidt system was given, and on page 828 Mr. Hunger described it more in detail, illustrating the vertical Schmidt boiler. In 1895, page 5, began a detailed investigation of the system by Professor Schroter, followed by results of trials and illustrations of the Schmidt vertical boiler and engine. In 1896, page 249, Professor Schroter gave the results of trials of a 1,500 H.P. triple-expansion engine aud of other engines, showing the progressive improvements due to superheated steam ; and on page 1245 he supplied a treatise on superheated steam- engines, with an illustration of the superheater between the cylinders. On page 1390 Professor Gutermuth gave results of trials of four different typea of engines with superheated steam, with an illustration on page 1420 of a superheater applied to a Lancashirc boiler. In 1897, page 1402, Professor A. Seemann gave a full investigation of the superheated steam question, dealing also fully with the experiments of Professor Ripper of Sheffield. This was continued on pages 1433 and 1464. In 1898, page 141, Professor Gutermuth again went into the question theoretically; and finally in 1899 Professor R. Diirfel summarised the subject, going very fully into the matter, illustrating the double-chamber cylindrical slide-valve referred to in Mr. Lenke’s Paper, and giving an extensive table of results of trials of various types of engines, with and without superheated steam. These articles began on page 601 and were continued at intervals

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Downloaded from pme.sagepub.com at UNIV NEBRASKA LIBRARIES on June 9, 2016 E 64 SUPEBHEATED STEAY IN ENGINES. SEP. 1901. throughout the year; the last was on page 1518, dealing with low- pressure steam. The following is a Memorandum of some of the Illustrations belonging to articles on Superheated Steam in the ‘‘ Zcitschrift des Vereines deutscher Ingenieure ” :- In 1894, page 828, Vertical Schmidt Boiler, with Paper by Mr. Hunger. In 1895, page 6, Vertical Schmidt Boiler, larger scale, with Paper by M. Schroter. In 1895, page 7, Schmidt Engine, Paper by M. Schriiter. In 1896, page 1248, Superheater between Cylinders, Paper by M. Schroter. In 1896, page 1420, Lancashire Boiler with Superheater, Paper by M. Schroter. In 1899, page 604, Double Chamber Cylindrical Valves for Superheated Steam, with Dorfel’s Paper.

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