*?13 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



LJutY, 



The suliject next considered is the engine itself, in which 

 •everal improvements are proposed. According to our autlior's 

 principle of confining himself to one exclusive model for every 

 jwirt of the steam-engine, he here selects the oscilhiting-cylinder 

 for universal adoption. The history of these cylinders as given 

 by the translator is curious, and affords interesting testimony that 

 a discovery, after being abandoned by the original inventor as 

 useless, maj' be taken up by others with complete success. In 1802, 

 Tkkvethick took out a patent for an engine, in which cylinder, 

 boiler, and furnace all muting together; and adds, that if it be 

 desirable, nil the other part.i may be fij:ed e.rcept the cylinder, which 

 may he suapended on trunnions or pimts perforated/or the admission of 

 xteam. Other patents were also taken out for moveable cylinders; 

 but the first oscillating-engines actually made, were those of Mr. 

 Aaron M.4nbv, and his son, the present able secretary of the 

 Institution of Civil Engineers. The important addition of the 

 hlide-valve was patented liy Joseph Maudslay, in 1827 ; who, by 

 combining the D valve with eccentric gearing, made an important 

 step in perfecting these engines. 



Dr. Alban proceeds to discuss the several objections usually 

 urged against the the oscillating-cylinder, and to explain its ad- 

 vantages. To the objection, that injurious lateral strains are pro- 

 duced every time the motion is reversed and the momentum 

 arrested, he replies, that in steam-engines of ordinary construction, 

 the ])arts subjected to reciprocating motion (the beam or side- 

 levers) are usually heavier than the cylinder, and vibrate through 

 a much greater arc. Though this be true, we must remark that 

 the arrangement of the oscillating-engine renders it mechanically, 

 or rather geometrically, impossible that its motion can be so even 

 and regular as that of the beam-engine. By the arrangement of 

 the ordinary crank, the motion of the beam is slowest at the two 

 limits of its motion : it comes gradually to rest at the extremity 

 of the arc of vibration, so that every thing like concussion is 

 avoided : and that this advantage is attainable in tlie most perfect 

 degree, is proved by the fact that in properly constructed 

 engines, the most ponderous beams move without producing a jar 

 or concussion. In the oscillating-engine, however, there is a pecu- 

 liarity in the arrangement which precludes uniformity of motion. 

 The arc through which the crank revolves wliile the cylinder 

 oscillates in one direction, is less than a semicircle — and greater 

 than a semicircle while the cylinder oscillates in the contrary 

 direction. Hence, if the motion of the crank be uniform, the 

 cylinder oscillates from riglit to left, and from left to right, in 

 unequal times. If, on the contrary, the oscillations of the cylinder 

 be regular, the crank moves faster when it is near the cylinder 

 than when at its greatest distance from it. In practice, these two 

 variations are compounded — or, if the phrase be allowable, the 

 irregularity of motion is shared between tlie crank and the cylinder. 

 Of course, the motion of the piston and other parts is affected by it. 

 The actual amount of it depends on the relation between the length 

 of the crank and connecting-rod, and the distance of tlie trunnions 

 of the cylinder from the centre of the crank ; and, cceteris paribus, 

 tlie uniformity is increased by increasing the distance of the swing 

 centre from the crank-shaft : but perfect regularity is unattain- 

 able. 



To the objection, that the cylinders are unequally worn by the 

 piston pressing first on one side and then on the other, the author 

 replies, that this objection can only apply with much force where 

 the pistons are large and heavy, and that the hemp packing (which 

 he always prefers to metallic packing) almost entirely remedies 

 the evil. 



The disadvantage arising from the friction of the trunnions on 

 which tlie cylinders swing, and which are usually perforated for 

 the admission and eduction of the steam, is remedied by the author 

 by suspending tlie cylinders — not on tlie gudgeons through which 

 the steam passes — but on a separate frame, having no communica- 

 tion with them. After enlarging on tlie great increase of friction 

 resulting from the heat of the metal, he shows that by keeping the 

 actual bearings on which the weight of the cylinder is supported, 

 separate from the steam passages, the heat of the rubbing parts is 

 comparatively trifling, and that a great amount of friction is conse- 

 quently avoided. 



The fourth olijection considered is, that " when the distance of 

 tlie trunnion-axis from the crank-shaft is too small, the vibrations 

 are unequal, as is also the force transmitted to tlie engine." To 

 this remark the translator briefly ro]dies, in a note, that " the 

 objection has no weiglit at all." With great deference to Mr. 

 Pole's authority, there is considerable weight in the objection. He 

 iias not appended to his dictum any reasons in defence of it, and 

 tliere is therefore hardly any other way of meeting him tlian by 

 counter-assertion. Does he mean to assert that the vibrations are 



performed in equal times? If so, it is quite clear, fiom the geome- 

 try of tlie case, that the crank moves at variable rates ; and this it> 

 suflScient proof that the force is not uniformly transmitted to the 

 %vorking parts. If, on the other hand, the motion of the crank and 

 the transmission of force be uniform, the oscillations of the cylinder 

 take place in unequal times. There is no escaping from one or 

 other of the horns of the dilemma. We do not insist on the disad- 

 vantage as necessarily serious ; but that it exists, and is unavoidable, 

 is obvious from mere inspection of a diagram showing the relative 

 positions of the cylinder and crank. 



The advantages of the oscillating-cylinder on which our author 

 earnestly enlarges, are — 1st, its simplicity, arising from the omission 

 of the beam, parallel motion, and other parts ; 2nd, the facility ol 

 construction, the fitting being in a great measure effected by the 

 lathe ; 3rd, compactness, and consequently suitability for steam- 

 vessels ; 4th, comparative lightuess ; Stli, the consequent porta- 

 bility ; 6th, diminution of prime cost ; 7th, the simplicity of work- 

 ing management ; 8th, the diminution of friction ; 9th, the saving 

 of grease for lubrication; 10th, the little repair required ; 11th, 

 the facility of discovering and rectifying any error of adjustment ; 

 12th, the omission of guides for the piston-rods; and lastly, the 

 direct and advantageous transmission of force. 



There is one remark to be made on this enumeration of the 

 advantages of the oscillating-engine, which, though simple, deducts 

 greatly from its claims to pre-eminence. — The greater part of the 

 merits claimed for it do not belong to it exclusively, but are com- 

 mon to all kinds of direct-action engines. 



Among the prominent features of Dr. Alban's views, is the pre- 

 ference which he tells us that long experience has induced him to 

 assign to hemp packing for the piston. Contrary to the opinion of 

 many practical men, who believe the metallic packing absolutely 

 indispensable for high-pressure engines, he considers that method 

 fraught with inconvenience. It may however be observed, that 

 many of the disadvantages (those arising from imperfect workman- 

 ship) are more likely to arise in Germany than in England, where 

 we may justly pride ourselves on the marvellous perfection which 

 has been obtained in the manufacture of the details of the steam- 

 engine. 



Other objections to metallic packing are not to be thus disposed 

 of. The cylinder and the piston are frequently of different metals, 

 and therefore liable to difl'ei-ent rates of expansion ; consequently, 

 the adjustment of the packing, though perfectly accurate when 

 the met.'ls are cold, becomes untrue after they are heated. Dr. 

 Alban denies that the packing gi-inds itself steam-tight by working ; 

 on the contrary, he believes that if any imperfection exist originally, 

 it is aggravated by use. We are however inclined to believe that 

 he speaks on this point from limited experience, for while the elas- 

 ticity remains unimpaired, it presses against the cylinder any 

 irregular protuberances which may exist, and the adjacent parts 

 are protected from attrition till these be worn down to an even 

 surface. Of course, if the elasticity of the packing be unequally 

 distributed, those parts most forcibly pressed against the cylinder 

 will wear thin and be destroyed before the portions of the packing 

 subjected to less pressure. 



The liability of the packing to lose its expansive power, either by 

 the component parts cohering and losing their mobility, or by the 

 heat destroying the elasticity of the springs, is strongly insisted 

 upon. It is also asserted that the complexity and number of the 

 parts render them liable to get out of repair, and that they can 

 never fit so closely as to be perfectly steam-tight. Hemp packing 

 is preferred on account of its simplicity ; and the author states, as 

 the result of his experience, that a packing of rope, of loose unspun 

 fibres, thoroughly lubricated, works well and remains steam tight 

 under high pressures. We will not absolutely assert that there 

 are not any circumstances under which this kind of packing may 

 be used with advantage, but many of Dr. Alban's prejudices must 

 have arisen from observing the working of metallic packing of 

 inferior construction; and probably, if he were acquainted with the 

 great improvements wliich have been effected in England in this 

 part of the steam-engine, he might be induced to modify his 

 opinions. 



There are many other topics of the treatise before us deserving 

 attention, but we must content ourselves with remarking, generally, 

 that the very original views taken by the author are not those of an 

 ingenious schemer merely, but of one who combines originality of 

 invention with practical knowledge, and enhances both by the 

 power of logical induction exhibited in the methodic arrangement 

 of his arguments, and the distinct statement of the results of his 

 experience. 



