1842.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



10 



have here described the sort of attention bestowed by the critics of 



the periodical press upon exhibited designs. Opinions as to their 

 merit they do not put forth, since they are unable either to form or to 

 express any ; but it is considered quite sufficient if tlie " infantile 

 paragraph " be tacked on to the rest, by way of postoript in some 

 such terms as " there are several beautiful architectural drawings, 

 on which our space will not permit to bestow more particular notice." 

 Or else "particular notice" goes to the extent of copying titles 

 and names from the catalogue, ticketed, perhaps, by some luminous 

 epithet, which leaves us just as mu;h in the dark as ever with regard 

 to the things so mentioned. For this neglect, architects have, in a great 

 measure, to thank themselves; first, for presenting their designs 

 before the public at the fag end of an exhibition of pictures, thrust 

 into a little poking room where not above one third of the drawings 

 hung up can be seen, much less examined. Secondly, because they 

 do nothing whatever towards promoting a popular relish for the study 

 of architecture, and vimlicating the pretensions assumed for it as one 

 of tiie fine arts. They at least have not much right to complain of 

 their designs being passed over without notice at exhibitions, when, 

 by the kind of notice they themselves generally bestow upon them 

 in their own publications, they convince us that they are unable 

 to explain their own ideas, or point out the etTect and character 

 at which they aimed. Ill does it become architects as a body to 

 regret that there should be so much apathy on the part of the public 

 towards their art, when they themselves display a degree of apathy 

 still more unaccountable if not very much more discreditable. 



MESSRS. MAUDSLAYS AND FIELD'S MARINE ENGINES. 



It must be unnecessary to offer a single observation upon the value 

 of the annexed table. Its value will, we are confident, be fully appre- 

 ciated by our readers. 



It is proper to remark, that several of the sizes not given directly 

 io the table are involved in other sizes which are given, and may be 

 deduced from them by a very simple process. Thus the length of the 

 stroke of the air pump, as well as of the hot water or feed pump, are 

 not given directly, but may at once be ascertained as follows : 



Given — Length of stroke of cylinder. 

 " Distance from centre of beam gudgeon to centre of cylinder. 

 " Distance from centre of beam gudgeon to centre of air pump. 

 From these data the length of the stroke of the air pump may easily 

 be obtained ; we have only to work this simple rule of three question; 

 — Distance from centre of beam gudgeon to centre of cylinder is to 

 distance from centre of beam gudgeon to centre of air pump, as length 

 of stroke of cylinder is to length of stroke of air pump: whence we 

 obtain the answer sought for at once. It is manifest that the answer 

 may also be obtained by construction. The feed pumps are, in Messrs. 

 Maudslays' engines, as well as in most other engines, worked off the 

 air pump cross head ; the length of the stroke of the air pump, there- 

 fore, determines the length of the stroke of the feed pump. 



The sizes given in the table have manifestly reference only to side 

 lever engines. The size of the steam pipe is not given in the table, 

 but the »ize of the steam port is, and the steam pipe should be, about 

 the same area. The quantity of lap or cover proper to be put upon 

 the valve, is a question determinable altogether by the quantity of 

 expansion required, and varies in different engines of the same power. 

 But the upper and under faces of the valve are, in Messrs. Maudslays' 

 engine, in no case of the same brcadtli : the cause for this inequality 

 is that if the valve be at half stroke, that is, with both ports closed, 

 and if the engine be moved round, the travel of the valve from half 

 stroke to the extremity of the stroke doicnwarda will be found to be 

 not the same as the travel of the valve from half stroke to the ex- 

 tremity of the stroke upwardn. In other words, the space described 

 by the valve whilst the piiton descends, and the space described by 

 the valve whilst the piston ascends, arc not iijual ; whereby it becomes 

 necessary to make the superior and inferior faces of the valves of 

 dilTurcnl depths, to compeosate for tl' is inequality. 



The accuracy of the preceding statement every engineer has it in 

 his power to verify, either by a model, or by a drawing of the valve 

 and piston in their several relative positions. The cause of the 

 irregularity may be traced to the oblique action of the coanecting and 

 eccentric rods. If the piston be placed at half stroke, that is, midway 

 between the top and the bottom of the cylinder, the crank will not be 

 level. This is manifest from the ordinary method of ascertaining tb« 

 length of the connecting rod, which is to level the beams, and take the 

 vertical distance from the extremity of the beams to the centre of the 

 crank shaft. When the beams are level the engine is at half stroke, 

 but if we wish to attach the connecting rod to the crank pin — its 

 length being ascertained as above — it will be necessary to bring the 

 crank down a little, to compensate for the depression of the head of 

 the connecting rod due to the deviation from the vertical line. If, 

 then, the crank be not level at half stroke, the descent of the piston 

 from half stroke, and its ascent to half stroke again will accomplish 

 more than half a revolution of the paddle wheels ; and the ascent of 

 the piston from half stroke, and its descent to half stroke again, will 

 accomplish less than half a revolution of the paddle wheels. The ratio 

 of the disparity will vary with the length of the connecting rod, the 

 circumstance of there being overhang or no overhang of the beam, the 

 length of the beam, and other circumstances; but in all ordinary en- 

 gines, the difference between the upper segment of the circle of the 

 crank's revolution and the under segment of that circle will interfere 

 with the valves' motion, and the proportionment of the valve faces 

 ought to have reference to the extent of that interference. 



It is Messrs. Maudslays' practice, in some of their very recent en- 

 gines, to make the stroke of the valve considerably more than twice 

 the depth of the port. All the valve levers are equal, and the stroke 

 of the valves is in all cases equal to the throw of the eccentric It is 

 also their invariable practice, in all engines of considerable magnitude, 

 to construct the valve casing with a faucet joint, to permit the ex- 

 pansion of the casing when heated with steam, without distorting the 

 cylinder. In some large engines which have been without this pro- 

 vision, we have known the cylinder ports to be rent asunder by the 

 expansion of the casing ; and however frequently and however well 

 the rust joints of the casing might have been made, they invariably 

 became very soon leaky, from the effect of unequal expansion. The 

 cylinder when hot will expand as much as the valve casing ; and if the 

 two were always equally heated, no detriment could ensue from the 

 absence of an expansion joint. But as the throttle valve is never per- 

 fectly tight, and iis the slide valve generally is so, the steam before 

 the engines are started enters the casing and induces its expansion; 

 whilst being excluded by the slide valve from the cylinder, the cylinder 

 is not heated, and therefore does not expand. Injury of some sort or 

 other, if the engine be large, is sure to be the result of these conflict- 

 ing forces. Our provincial engineers are sadly deficient in their 

 acquaintance with or their attention to details such as those to which 

 we have adverted ; yet it is upon an attention to such details that the 

 superiority of an engine principidly depends. 



In the double cylinder engines of the Messrs. Maudslays, cylindrical 

 slide valves are employed, and have been found to operate extremely 

 well. The packing of these valves is metalli.:. The packing of the 

 pistons made by the same firm are invariably nict;Ulic, and generally 

 consist of a single ring turned eccentric, cut in one place, and the cut 

 part fitted with a tongue piece to prevent the steam /ron. p issing 

 through the cut. A piece the same breadth as the ring is httcd over 

 the back of the cut, ground tight, and then rivetted to one part of the 

 ring. The elasticity of the ring is in most cases found sulhc.ent to 

 keep the ring in intimate contact with the interior of the cylinder, an.1 

 the force with which this contact is maintained may be either aug- 

 mented or diminished bv a bridle-a truly ingenious contriv.ince, and 

 one which we regret the limits of this notice prevent us from referrinR 

 to more specifically. 



In a future paper we shall probably enter with considerable minute- 

 ness into the merits of Messrs. Maudslays' machinery, or rather into 

 those details which constitute the excellence of the machinery of that 

 eminent firm. 



T i. 



