1850.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



273 



ON CONDENSING STEAM ENGINES. 



( Jnth Enyravings, Plate X.) 



On the Condensation of Steam in the Engines of the South Stafford- 

 shire Iron District, and the Improvements to lie effected in than'. By 

 William Smith, of Dudley. — (Read at tlie Institution of Me- 

 chanical Eiigineors.) 



The object of the present paper with the accompanying' series 

 of Indicator Diagrams, which liave been taken from tlie several 

 engines by the autlior of the ])aper, is to show the present worl\iiig 

 condition of forty-eight of the largest class of mill, forge, and 

 blast engines in South Staffordshire, with some remarks as to the 

 practicability of improving them. 



The general character of the Indicator Diagrams of the majority 

 of these engines, shows a considerable pressure of steam, con- 

 tinued nearly uriifiirm througliout the whole stroke of the piston, 

 and averaging about I'J lb. per square inch above the atmosphere 

 in the forge and millengines, and about 7 lb. jier square inch in the 

 blast engines; with a very defective vacuum, conmiencing about 

 the atmospheric line, and reaching only from 7 lb. to 11 lb. |)er 

 square inch below the atmosphere at the end of the stroke, the 

 average vacuum being about 6;^ lb. per scpiare inch below tlie 

 atmosphere throughout the stroke. Some of the Indicator Dia- 

 grams from blast engines show a considerable expansive action, 

 but not a good vacuum. 



Fig. 3, Plate X. shows the Indicator Diagram from a mill 

 engine of la-inch cylinder and 7 feet stroke, making 17 strokes 

 per minute, which was working very imperfectly in the condensa- 

 tion of the steam, and has been improved to a remarkable e.\tent, 

 by an altenitiim made for tlie imqiose of improving the vacuum, 

 which has effected a very considerable saving in the consunijition 

 of fuel. This engine was working with I'i^ lb. pressure of steam 

 at the beginning of the stroke, continuod to l/.i, lb. pressure at 

 the middle, and reduced to 6 lb. per inch at the end of the stroke, 

 by wire-drawing the steam without any cut-off expansion-valve; 

 the average pressure being l(i-37 lb. per sipiare inch throughout 

 the stroke; the average vacuum was only 2'72 lb. per square inch 

 below the atmosphere, beginning a little above tiie atmospheric 

 line, and reaching only 5 lb. below the atmosphere at the end of 

 tlie stroke. This performance being so bad it was considered ne- 

 cessary to examine the engine, and the cause was found to be from 

 the valves, thoroughfares, and condenser, being much too small 

 for the ])roper proportion, the steam and educti(ui valves being 

 only 7 inches diameter, and the thoroughfares of the same size; 

 these were therefore removed anil replaced by others, the steam 

 valves being 10 inches diameter, and the eduction valves and 

 thoroughfares 12 inches diameter, or three times the area of the 

 original ones. The condenser was also nearly doubled in capacity 

 by attaching a large vessel on the top of it, which made it rather 

 larger than the regular proportion; the air-pump was only 2i 

 inches diameter, with half the stroke of the steam jiiston, or 

 about one-fifth less contents than tlie regular proportion for the 

 size of the cylinder; this was not altered, but there was an abund- 

 ant sujiply of C(dd water for injection. 



The result of the above alteration is shown by the dotted lines 

 12 A, fig. 3, the steam pressure being 8 lb. at the beginning, and 

 reduced to about the atmosphere at the end of the stroke, the 

 average being 5- 10 lb. instead of lC-37 lb. per square inch pressure 

 throughiuit the stroke; the vacuum commenced at 10,1 lb. and 

 ended at II lb., the average being 10-15 lli. instead of 2-72 lb. per 

 square inch below the atmosphere throughout the stroke. Tlie 

 improvement in the vacuum amounts therefore to a constant 

 average pressure of 7-43 lb. per square inch throughout the stroke; 

 the total power of the engine as shown by the first diagram, was 

 19-09 lb. per inch on the piston throughout the stroke, being 190 

 horse-power, consequently this improvement of the vacuum 

 amounted to 39 per cent, of the total power of the engine or 74 

 horse-power. 



The mode of effecting the above alterations (No. 12 Engine) is 

 shown in ligs. 1 and 2, I'late X. Fig. 1 shows the engine before 

 the alteratiim, the steam valves S, the eduction valves E, and the 

 thoroughfares T being only 7 inches diameter. Fig. 2 shows the 

 engine after the alteration, the steam valves S are increased to 

 10 inches diameter, and the eduction valves E and thorough- 

 fares T are 12 inches diameter; the new valves being so much 

 larger than the old ones, a different arrangement was required to 

 make room for them, the spindle of the lower steam valve being 

 carried up the side pipe, as shown in fig. 2, and the upjier educ- 

 tion valve placed over the other side, pipe, so that three of the 



No. 156. — Vol. XIII. — September, 1850. 



valve spindles are worked at the upper steam chest, and one only 

 at the lower. The addition made to the condenser is shown at C, 

 fig. 2, which was a circular vessel constructed of boiler plate, 3 

 feet 6 inches diameter, and 15 inches high, fixed on the top of the 

 condenser. A further improvement was also made in the con- 

 denser, by cleaning out the deposit of lime, and adding an internal 

 injection pipe and rose P; there was no internal injection pipe pre- 

 viously, but simply a hole in the side of the condenser, where the 

 injection-cock A was fixed on, as shown in fig. 1, and consequently 

 the injection water was much less efficient in condensing the 

 steam, being ])oured into the condenser in a single stream instead 

 of being scattered in a number of small jets from the rose end of 

 the pipe. 



The majority of engines in this district are similar in this 

 respect, and the reason that has been given is, that the rose is 

 apt to get the holes choked up by deposit from the water, which 

 is very much impregnated with lime. This is a matter requiring 

 particular attention in this district, and cases have come under 

 the writer's observation, where condensers were filled up by the 

 deposit in the course of two or three years' time, to such an extent, 

 that the capacity was reduced fully one half, as well as the passage 

 through the foot valve; it is a very hard calcareous deposit 

 which adheres firmly to the cast-iron, and requires considerable 

 labour to cut it out, involving a serious stoppage of the engines, 

 and they were consequently worked as long as possible before 

 taking off the condenser cover to cut out the deposit, which 

 increased to 7 inches thickness, and as much as half a ton weight 

 in one engine. Besides the very important saving effected by the 

 greater povver obtained from the steam, in consequence of the im- 

 provement of 39 per cent, in the vacuum, as described above, the 

 engine has been found to do the work more regularly and satis- 

 factorily since '^the alteration, than before; it was liable to be 

 pulled up by any extra strain of the rolls, &c., whenever the pis- 

 ton was getting in want of repacking, the leakage of steam 

 injuring the vacuum on account of the very deficient condensing 

 power; but that has not occurred since the alteration was made. 

 The engine drives a merchant mill of 3 pair of rolls, a guide 

 mill of 3 pair, 2 pair of forge rolls, a forge hammer, 2 shears, 

 and a pump for draining the foundations. It was not stopped 

 longer than three days to make the whole of the alterations 

 described above. 



Another similar engine of the same size as the preceding, 

 was also examined, in consequence of the imperfection in its 

 condensing, and the valves and thoroughfares were found to be 

 10 inches diameter, but the valves had not sufficient lift, the 

 eduction pipe to the condenser was 9 inches diameter, and the 

 condenser was 2 feet 4 inches diameter, and 4 feet 6 inches high; 

 the eduction pipe was then removed and replaced with one 12 

 inches diameter, also a large vessel was fixed on the top of the 

 condenser, which increased its capacity about one-third. The 

 lift of the valves was then increased from l| inch to 2f inches, 

 and the result of the alteration was an improvement in the vacuum 

 of from r50lb. to 7-97lb. per square inch below the atmosphere, 

 or 6-47 lb. per square inch increase of average pressure through- 

 out the stroke. 



The saving of fuel from these alterations has not been well 

 ascertained, as the engines in both cases are worked from a 

 series of boilers which also supply steam to other engines upon 

 which the load is very unequil, but the saving is admitted to be 

 very considerable, and in the case of No. 17, the proprietors have 

 been enabled to use an inferior description of slack, and also to 

 throw off one boiler, with a fire grate about 7 feet square, and 45 

 square yards of heated surface, without any diminution in the 

 power employed. 



The aggregate power of the 45 mill, forge, and blast engines 

 from which the Indicator Diagrams are taken, is nominally 3240 

 horse-power, according to Boulton and Watt's proportions of the 

 cylinders, but by the calculation of the Indicator Diagrams, the 

 total is 7819-horse povver; the average vacuum obtained in the 

 present working of all the engines is about Gib. per inch below 

 the atmosphere throughout the stroke, omitting from the average 

 four, which are exceptions to the general run of these engines; 

 and the average vacuum obtained in the six expansive engines, of 

 which Indicator Diagrams are also given, is lo^lb, per inch be- 

 low the atmosphere throughout the sti'oke. The loss of power 

 from the imperfect vacuum in the former engines may therefore 

 be taken at the difference between these pressures, or 43lb. per 

 square inch pressure throughout the stroke, which amounts to 

 1930 indicated horse-power u|ion these engines; or in other 

 words, an additional power of 1930 horse-power, or 25 per cent, 



3? 



