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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Ogt. 



qiiainted, by experience, with llie fact that lliere is no heat given out by 

 high-pressure steam when escaping into tlie air, having often held our 

 hand in a jet of steam issuing from a pressure of 100 lb. to tlie square inch. 

 It is only when surh steam regurgitates, if we may so express it, that it 

 gives out heat and scalds. When, for example, a jet of steam strikes 

 a''ainst a solid body, and its issuing force is arrested, then it scalds ; hut 

 when it has tree room to expand, the sensation produced is that of cold, 

 and not of burning. It may be rcnienibered that when by the separation 

 of the pipe of the boiler in an engine constructed by Messrs. Samuda, at 

 Blackwall, several persons were killed, they all lost their lives by the 

 scalding of the low-pressure steam. The high-pressure steam of the 

 Cricket's boiler, on the contrary, did not seriously injure a single individual. 

 This extraordinary property of high-pressure steam should form an im- 

 portant consideration in determining the comparative safety of the two 

 kinds of engines, yet it has hitherto been disregarded. 



Since the foregoing remarks were written, the evidence of Mr. Lloyd, 

 chief engineer and inspector of machinery of the Royal Navy, has been 

 given at the adjourned inquest, held on the 22iid September, and we sub- 

 join the greater portion of it, divested of the repetitions consequent on 

 examination by dilferent counsel. Some parts of his statements relative to 

 the construction of liis boiler and the pressure borne on diil'ereut pans are 

 not very clear or comprehensible, but his evidence proves that the boiler, 

 however defective, was capable of bearing a pressure twice as great as 

 that which would have lifted the weighted valves, if they had not stuck or 

 been tied down. The corresponding boiler of the Cricket gave way under 

 a pressure of 1361b. to the square inch, but it had previously sulTered a 

 Teat strain by the pressure which caused the explosion, and therefore its 

 strength at the time must have been much greater. Mr. Lloyd is of 

 opinion that the other boiler must have had a pressure of at least 136 lb. to 

 the square inch before it exploded. 



Clark, the engineer, was examined after Mr. Lloyd, and he declared that 

 the statements of the other witnesses against him were false, and that he 

 never gave directions to Edwards nor to any one to tie down the valves. He 

 seems to make a nice distinction between tying them down and twisting 

 the end of the siring fastened to the lever round a nail. He denied, how- 

 ever, that the string was ever tight, and he said that the object of twisting 

 the ends round the nail was to prevent them from dangling and being in 

 the way. 



Mr. Lloyd's evidence was to the following effect :— 



The Engines. — " With regard to the engines themselves, I do not think 

 many observations necessary. They are high pressure engines, on the 

 principle well known as Wolfe's. Each engine has two cylinders ; in one 

 the steam is used at a high-pressure, and, instead of passing into the open 

 air, as in an ordinary high-pressure engine, it passes into the second and 

 larger cylinder, whence it passes into the condenser, and is there condensed 

 in tlie ordinary way. The object of this arrangement is of course the sav- 

 ing of fuel, by effecting a saving of steam, and, therefore, of fuel. So far 

 as I saw, the materials and workmanship of the engines were good. As 

 compared with high-pressure engines, there is nothing objectionable in 

 these engines, in point of danger — nothing but the ordinary construction. 

 There were attached to the engines two pumps for feeding the boilers ; 

 another pump was worked by an auxiliary engine, which was commonly 

 called the ' donkey ;' and there was a fourth pump, to be worked by the 

 hand, for feeding the boilers. These appeared to be all that was neces- 

 sary. 



The Boilers.* — There were two boilers, consisting of an external cylinder, 



* [The annexed diagram, from the " Mining Journal," is a section of tlie boiler show- 



Ove feet in diameter, having a hemispherical end at the back, and the front 

 being composed of a flat plate. To this flat plate are lixtd a c) liuder, 

 forming the furnace, and all the small tubes through which the products of 

 combustion pass. The internal part of the boiler, con.sisting of the furnace, 

 the fire-box, and the small tubes, were secured to the shell by tlie rivettiug 

 ronnd the circumference of the front plate, and by two slays, one lixed be- 

 tween the end of the fire-box and the end of the boiler, and the other fixed 

 obliquely between the top of the front and the upper part of tiie shell. A 

 steel dome was also rivetled to the top of each boiler, on each of which 

 were two safety-valves, pressed down by levers, one lever having a weight 

 at its end, and the other a Sjiring-balance— Salter's balance. The thickness 

 of the tube plates vias J inch ; of the front-plates, those on the top and bottom 

 of the tube-plates, 1 inch ; the shell finch. 'I he front of the boiler con- 

 sisted of three plates, one of these being the tube-plate, and the others the 

 plates above described. The steam-dome is ■,% inch ; the angle-irou round 

 ihe front of the boiler is 3 inches by J inch. All the other angle iron is 2J 

 by f inch. The rivet* in the boiler are j inch diameter, and ihe rivets iu 

 the steam-dome rather smaller. That includes the rivets in the shell ; all 

 the rivets of any importance are | inch. Assuming each boiler to be of 

 the power of 16 horses, the total heating surface in the boiler is 14'8 square 

 feet per horse power. The area of the fire-graie is 5o-100tbs of a foot per 

 horse power. There is nothing objectionable in these proportion.*, either 

 in the amount of area of firegrate or of heating surf.ice. The quantify of 

 water in the boiler up to the middle gauge-cock is about 3B'l cubic feet 

 per horse power ; and the steam-room about IJ foot per horse power ; that 

 is including the dome and the other part of the boil«r. 



The Valves and Pressure.- -\ have calculated the pressure upon the 

 safety-valves, supposing ihe weight to be at the extremity of the lever, at 

 very nearly 66 lb. per square inch. Taking the spring-balance as it was 

 when I saw it, the pressure per square inch when the valve was just about 

 to open, would be 40 lb. per square inch ; but if the valve were as wide 

 open as it could be, this spring-balance would produce a pressure of about 

 170 lb. per square inch. Both valves are lever valves ; one is pulled down 

 at the end by the spring-balance, the steel-yard, the other is operated on by 

 a weight. As the lever of the spring balance rises, by the valve opening, 

 the pressure on the valve increases, and rises to 170 lb. at the liighest. 

 One pound on the spring-balance produces a pressure on the valve of nearly 

 two pounds. These valves operate jointly on the boiler, both serving to 

 empty it of steam ; but they operate separately from each other. I think 

 if they had all been properly in operation, the steam could not have accu- 

 mulated in the boiler to any dangerous extent— that is, supposing them not 

 to have been overloaded. I do not approve, certainly, of the arrangement 

 of this spring-balance valve ; it is objectionable because, when the valve 

 has been raised to such a height as to relieve the boiler considerably, the 

 pressure brought upon it is very greatly increased, the power of the lever 

 being nearly as lu to 1. This is not the usual way in which spring- 

 balances are used, so far as I know. 1 think Ihe principle wrong, on ac- 

 count of the pressure being increased when the valve opens. I think it 

 wrong in principle to put a spring-balance at the end of a long lever. I 

 altogether object to valves being in the power of Ihe engineer to load at bis 

 pleasure, especially the high-pressure ones ; but it is only fair to say that 

 Ibis is too commonly the case. It can scarcely be a matter of opinion that 

 this is wrong in principle. Nothing in the weighted valves called for ot)- 

 servation, except that if it had not been intended to work these boilers at a 

 pressure of 06 lb. to the square inch, such a weight as that ought never to 

 have been put upon the lever. The same remark applies to the spring- 

 balance valve, because it can be screwed down or up to au) extent. The 

 weight being upon the lever was objectionable, as it would be an indica- 

 tion to the engineer that he might use it in any way he thought fit, so as to 

 obtain that pressure, namely, 66 lb. 



Opinion on the Strength oj' the Boiler. — As to the construction of the 

 boiler, 1 may say that, in my opinion, it is dangerous to be used as a high- 

 pressure boiler. The whole of the pressure of the steam nilliin tlie boiler 

 is brought, either directly or indirectly, upon this flat plaic in ihe front. I 

 find, when the pressure of steam is 661b. on the square inch, the direct 

 pressure on this plate is 83 tons, which is withstood entirely by the stillness 

 of the plate itself, with the small addition of the two stays before mentioned. 

 I do not believe that 601b. ou the inch would have burst the lioilcr at pre- 

 sent, though it might have done so when the boiler was somewhat older. 

 The objections which naturally lie against a flat plate of this kind are 

 these : In the first place, you cannot calculate what it ought to bear; the 

 pressure on the inside of it tends to produce three different effects. First, 

 there is a strain brought upon it at right angles to the surface, and, if the 

 plate were perfectly rigid, there would be no other effect ; Ihis not being 

 the case, an enormous pressure is brought upon it in its own plane, which 

 may be illustrated by considering the etfect produced on a musical string 

 when pressed sideways, the force brought to bear upon it lengthways being 

 far greater thau when stretched in that direction. A third actiou is pro- 

 duced by the bending of the plate, the outer circumference remaining nearly 



ing the position of the two stays, tlie only ones in the boiler. A I, is the stay at the 

 front, leading froo] the front plate, in a ditigaiial direction, towards the bteuni dome -, tt)i« 

 stay being formed out of l^ inch square bar-iron, dattened out at the end with an initi 

 linle, and supported by a pin passing tiirough two L'Jinch antde irons. A 2. represems 

 the other stay, leading from the back of the boiler to tiie end ot the flue, which communi- 

 cates with the tubes. A, the lurnace, about 3 feet iu diameter. U, the steam domu, la 

 wtikh two safety-valves weie aitixed. C, steam-pipe, leading from the box of thu salety 

 vaive to the funoel O. E, represents the spun-yaru, with which It is supposed tllevalYcA 

 were made fast.] — Ed. 



