1845.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



283 



12 TrftiDS per day each way ; 



Coal (as before) usefully burnt, 76 lb. per train, add for wa 



cenl., or X7 lb. . - - - 



112 X 6 engine s ~ 33 _!j^ ji,. coal at 10s. per ton. 



20 mites 

 Knglnemen'i wages (as before) : 

 98. lid. X 8 sets . . - - 



J4 trains X JO nillei 

 Repnh 



LMKl/ 



s (as before) : 



'J4 iruliis X 20 miles x 36!) days 

 PlstoD leathers - - - 



Chareool - - - 



Wear and tear of travelling piston gear 

 Train comluttors, 4 men at 6s. each : 



104 

 . n-25 

 .012 

 .010 



I'Us 

 24 trains x 20 miles 



Maintenance 

 Of groove, I 



per mile - - '"* 



24tri 

 Composition, 15/. per year per mile lOd. - 



24 

 Of continuous valve, &c. 501. 2s. 9d. per day 

 24 



34 Trains per day each way ; 

 Coal (as before) usefully burnt, 75 lb. per train, 

 add for waste, 40 per cent. 30 ,, 



Per 7' rain per Mile 



1051b. 

 = 31-5 lb. at IDs. per ton 



48 trains x 21 

 Repairs. &c. to 



j*20o X : 



ngines (as before) : 



4» iriiins X 20 miles 

 Piston leathers - " ' 



Charcoal - - 



Wear and tear of travelling piston gear 

 Train conductors, 8 men. at 53. each : 



48 trains x 20 miles 



Per train pe 



48 trains 

 Composition, 15/. per mile per year = lOd. per day 



Continuous valve, &c. 50/. per ye 



= 20 

 ■0-63 



■ 0-63 



Intemipiion of Traffic. — Worked with a stationary power, a single line 

 will on the whole he liable to less interuptions than a double line worked 

 with locomotives — (Brunei.) 



Leakage. — I. Generally. — II. Loss of Power on the Atmos]>heTic System 

 from Leakaye. — III. Principle Causes of Leakage ; how far, in the progress 

 of Improvement, it is likely to be prevented. 



If the tube be properly cast, there will be no leakage whatever through 

 the iron — (Field.J The increasing pressure of the atmosphfre at a high 

 vacuum closes the valve more firmly and prevents additional leakage — Ro- 

 binson. The leakage increases with the vacuum. Calculations as to the 

 amount of leakage on the atmospheric system ; experiments made by witness 

 at Dalkey — [Stejthenson.) 



" We may state that there are three kinds of power available for railway 

 purposes ; the first is that of stationary engines with robes, which may be 

 applied either to hilly countries or flat countries, as it is done in the north ; 

 the second is the locomotive system ; the third is the atmospheric. I be- 

 lieve in point of power, the cost nf producing a certain amount of availalile 

 power, I mean power practically available, is very much the same. In the 

 case of a stationary engine, you have the whole of the power communicated 

 to the train except that which is absorbed by the engine itself, or by the 

 friction of llie rope, which of coarse is power created for the purpose of mov- 

 ing the machine, and bringing the available power into action. In the case 

 of the locomotive system you have an objection, arising from the engine it- 

 self, which is a ponderous machine ; whenever you move from a level, the 

 weight of the engine acts against you. You have also a disadvantage in the 

 locomotive system, viz. that you caunot employ a condensing engine ; that 

 is, you cannot emploj a vacuum, therefore you are obliged to employ an en- 

 gine which has the resistance of the air to contend with, and in the other 

 case you have a vacuum. That is a drawback which must inevitably be ap- 

 plied to the locomotive engine. The proportion of the gross power developed 

 bjr the engine bears very nearly the same proportion to the gross power that 

 the friction of the rope does to the engine ; it is very approximate; in some 

 case it will be more and in some less; for example, it is clear that the fric- 

 tion of the rope in the case of a stationary engine will depend upon (he length 

 of the plane worked by the engine or the rope ; for instance, if you have an 

 engine working a plane of one mile in length you have the friction of the 



rope lost, which is due to one mile ; if you work it two miles you have twice 

 the pcr-centage of loss in the gross quantity of power developed by the en- 

 gines. Then with respect to the atmospheric, I have gone very carefully into 

 that question ; you have the leakage, you have no friction of the engine it- 

 self, which of course is just the same as in the case of common stationary 

 engine ; therefore the comparison between the atinospberice and the sta- 

 tionary engine is simply a comparison of the friction of the rope and the 

 leakage. Now the leakage it is difficult to compare exactly with the friction 

 of the rope, because the effect of the rope is constant, the quantity of the 

 power lost being constant. 



"The effect of the leakage is varying at every pressure. Suppose you 

 worked the atmospheric engine constantly at 2 or.'! inches, the leakage would 

 be very immaterial. In my experiments at Dalkey, it amounted to 250 feet 

 per minute ; the horse power necessary to pump those 250 feet per minute 

 was the loss; then, as you go on, if you increase the load, requiring therefore 

 a higher vacuum, that is, increase the height of barometer from 2 inches, 

 say, to 10, that is in the proportion of 1 to 5, that loss of 250 feet is changed, 

 because the punip itself can only pump its own contents out at each stroke ; 

 the vacuum existing in the pipe at the density of the atmosphere is expended 

 so many times inversely in proportion to the height of the barometer, or 

 rather, in proportion to the cold remaining, not in the proportiiyn of 2 to 10, 

 but in the proportion of 28 to 30. What I mean to say is shortly this : 

 that, as you increase the load in the atmospheric, or as you increase the ne- 

 cessity of working with a higher vacuum, you make the atmospheric worse 

 than the rope; but as you decrease the vacuum at which you work, you 

 make it better than the rope. Ihere is an intermediate point, and that ap- 

 pears to have been by pure accident, at the Euston station, where the fric- 

 tion of the rope, and the loss by that friction, is as nearly as possible equal 

 to the loss by leakage at Dalkoy, according to my experiments. It appears 

 that B mile of double rope is equal to about a mile and a half of atmospheric 

 pipe; there they appear to be as nearly as possible equal. I think it is an 

 error to attribute the whole of the leakage to the intermediate pipe. The 

 question was raised when I was in Dublin by the late Mr. Samuda, and I 

 then considered the matter. Ibe intermediate pipe between the valve pipe 

 and the pump had been prepared carefully; he told me that it had been 

 pitched and covered with tar. I am perfectly aware, from experience, that 

 a ver)' slight covering of that kind is capable of rendering a cast-iron pipe of 

 that description perfectly air tight ; and the comparison of the leakage be- 

 tween the valve pipe and the pump was rather in favour of the close pipe 

 and pump; the valve pipe was almost the better of the two, involving this 

 necessity, that the pipe witliout the valve was little better than the pipe with 

 the valve. But the real fact was this, and it was an oversight in the print- 

 ing of that part of my report where I distinguish between the leakage of the 

 one and the leakage of the other. I say, ' the leakage of the valve-pipe and 

 the leakage by the connecting pipe ;' it ought to have been, ' the leakage in 

 the pump;' for a very large proportion of the leakage, in my opinion, takes 

 place, not in the connecting pipe, but in the pump itself. It is the place 

 where it is most likely to arise ; it is a place where there is a good deal of 

 nice workmanship, and where a good deal of derangement or wear and tear 

 goes on ; it is therefore much more natural to attribute the leakage to that 

 which is continually exposed to wear and tear than to that which is not so 

 exposed. Therefore, to attribute the whole or any of the leakage to the con- 

 necting pipe is not, in my opinion, a correct representiou of the fact." 



The leakage diminishes as the train passes along, as a less surface is ex- 

 posed ; the velocity becomes more irregular as the train approaches the end 

 of the pipe — {Stephenson.) 



"When the train was coming close to the end of the pipe, the quantity of 

 air remaining in the pipe bore so small a relation to the contents of the pump 

 itself, that the velocity came to be irregular, and it gave the train, just as it 

 was going from the pipe, a sort of kick, an acceleration ; but so long as the 

 quantity of air in the pipe bore a considerable proportion to the quantity of 

 air which the pump was capable of extracting at one stroke, the velocity re- 

 mained exceedingly uniform, and the barometer extremely steady. I made 

 experiments at 23 and 24 inches, and tliere was a constant loss of power; as 

 the vacuum was increased and tlie load increased to correspond , there was a 

 diminution of velocity. It was very strikingly illustrated by those experi- 

 ments. It has been broadly stated by some persons that the velocity has no 

 relation to the load, or in other words, has no relation to the gradient. Now 

 ' load' and * gradient' are, as I stated before equivalent terms. A load of 24 

 tons obtained a maximum veloiity of 36 miles an hour ; and as we went on 

 increasing, when we came to a load of 50 tons the maximum velocity was 21 

 miles, and the barometer stood at 22 inches ; in the other case the mercury 

 in the barometer stood at 13 inches. Leaving the 50 tons, and going on to 

 CO tons, the maximum velocity then was 18 miles an hour ; when we got on 

 to 64 tons it sunk to about 17 miles an hour, so that as you go on increasing 

 the load you get a corresponding and constant diminution in the velocity ; 

 in fact, as the engine power was uniformly exerted, as might be expected, 

 with a larger load you have a less velocity." 



A slight leakage would produce a vacuum between the valve and the piston 

 before the starting of the train, but this would be a very sHght imperfection 

 in practice — {Field.) 



ibe power of the stationary engines has been calculated at a speed of 

 eighty miles an hour, or sixty miles allowing for leakage — [Brunei) 



The leakage is found to be in proportion to the length of the tube, and 

 not to vary with the power at which it is worked — {Robinson.) 



The real loss of pov.er is the leakage. This increases in elTect as the va- 



