1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



109 



DOUBLE CYLINDER STEAM ENGINE. 



Deacriplion of a Double Cylinder Rolalivt Steam Engine, erected by 

 Messrs. G. and J. Rennie, at Mr. Thomas Ciibilt's Factory, near 

 f^'aiixhall Bridge. 



This engine is entitled to the attention of all who are interested in 

 the economical production of steam power. For a rotatory engine its 

 consumption of fuel is believed to be unpreeedentedly small ; and we 

 are convinced we shall render an acceptable service to our readers by 

 informing them of the peculiarities of its structure, and the nature of 

 its performance. 



The arrangement of the parts of the engine is identical with that of 

 the beam rotative engines in common use, with the exception that the 

 motion is derived from two cylinders instead of from one. The em- 

 plorment of two cylinders, the pistons of which are worked by the 

 same steam, was first practised by Hornblower, and extemled and 

 improved upon bv Woolfe ; but the plan has never come into general 

 use. In this engine the smaller cylinder is one-fifth of the capacity of 

 the larger cylinder, and the expansion takes place in the larger cylin- 

 der exclusively. The steam enters the smaller cylinder direct from 

 the boiler during the whole of the stroke; and having pressed down 

 the piston, escapes, not into the atmosphere or into the condenser, but 

 into the larger cylinder, where it becomes instrumental in forcing the 

 piston of the larger cylinder upwards. The same steam, therefore, is 

 rendered available in the production of power in both of the cylinders, 

 and it is only after having accomplished this end that it escapes into 

 the condenser. 



The piston rods proceeding from the cylinders are attached to the 

 same end of the beam, the rod of the larger cylinder at the extremity 

 of the beam, and the rod of the smaller cylinder at a point nearer the 

 main axis. The pistons, therefore, act in concert ; and by a proper 

 arrangement of the valves, a communication is maintained between the 

 space beneath the piston of the smaller cylinder and the space above 

 the piston of the larger cylinder, so that the pistons descend simul- 

 taneously. 



The engine is supplied with steam by one boiler, which is cylin- 

 drical, and is, in its details, of the most approved Cornish construction. 

 The exterior diameter of the boiler is 6 ft. 3 in., the extreme length 

 34 ft., and the pressure of the steam 28 lb. upon the square inch. 

 The fire grate is situated in an internal flue tube, 3 ft. S in. in diameter, 

 which extends through the boiler, from end to end. The length of the 

 fire-place isl ft. (j in., its breadth 3 ft. S in., and its mean height Is in. 

 The coal burned is Graigola, an excellent and economical species 

 of Welsh coal, which produces no smoke. The depth of coals upon 

 the fire bars is never permitted to exceed 3 inches, so that there is 

 little or no carbonic oxide generated. The combustion is slow, a con- 

 dition favourable to its perfection, and as the intensity of the fire 

 scarcely exceeds that of a common household grate, there is no clinker 

 formed. The fire bridge is composed of brick, and instead of being 

 flat upon the upper surface, as is the case in many boilers, is formed 

 to a circle nearly concentric with the circle of the flue tube, and 

 leaving only a few inches of opening between the convex surface of 

 the bridge and the concave surface of the flue tube. By this expedient 

 the flame and hot air proceeding from the fire are spread in a thin 

 sheet over the interior surface of the flue, by which means their heat 

 is more rapidly and perfectly communicated to the water in the 

 boiler. 



Between the fire bridge and the farther extremity of the boiler a 

 tube extends longitudinally through the flue. This tube contains 

 water; it is alout 25 inches in diameter, ami communicates in two 

 places with the water in the boiler. f)ne of these communications is 

 through a vertical pipe, exlemling from the under side of the flue tube 

 to the under side of the horizontal pipe containing water, and situated 

 immediately behind the bri'lge. The other communication is through 

 a copper pipe at the after extremity of the boiler. This pipe is 31 in. 

 in diameter; it springs from the upper side of the horizontal pipe, 



and, passing to the outside of the boiler, ascends until it reaches the 

 level of the boiler top, when, bending over, it penetrates the shell of 

 the boiler, and descends internally until it reaches to the depth of a 

 few inches below the water level. Through this arrangement of pipe* 

 a continual current of steam and water is maintained. 



The hot air, upon leaving the furnace, travels through the internal 

 flue, communicating iU heat both to the water io the boiler and to the 

 water contained in the horizontal pipe situated in the flue which we 

 have just described. Upon arriving at the extremity of the internal 

 flue, the current of hot air is separated into two streams, on<" of which 

 traverses the one side of the boiler, and the other the other side of the 

 boiler. These streams, upon arriving at the front of the boiler, again 

 unite; they then descend, and pass longitudinally beneath the bottom 

 of the boiler, after which they enter the chimney. In the passage 

 which unites the flue beneath the bottom of the boiler witli the chim- 

 ney, a long pipe is placed about lo inches in diameter, and into this 

 pipe the water em;iloyed for feeding the Ixjiler is first introduced. By 

 this arrangement the air proceeding to the chimney is robbed of its 

 superfluous heat, and escapes into the atmosphere at a comparatively 

 low temperature. 



The pressure of the steam in the boiler is indicated by a syphon 

 mercurial gauge, graduated to feet, inches, and quarters of an inch. 

 The level of the water in the boiler is regulated by a feed cock, 

 adjusted from time to time by the engineer. The usual ajiparatiis for 

 feeding by a head of water, with a valve operated upon by a float, 

 would require to be of inconvenient dimensions if applied to this 

 boiler, on account of the superior pressure of the steam to that of 

 ordinary land boilers. There is a glass gauge tube and the usual 

 gauge cocks for the indication of the water level. 



The boiler is furnished with two steelyard safety valves, and one 

 safety valve situated within the boiler and inaccessible to the engineer. 

 Four brick walls enclose the boiler, and a 9-inch brick arch extends 

 over its top. Between this arch and the external surface of the 

 boiler a space of an inch or two is left, to leave room for the expansiou 

 of the boiler. Above the brickwork there is a layer of charcoal 

 about a foot in depth, for the purpose of preventing the escape of heat 

 from the boiler; and the precautions adopted have the etTect of ren- 

 dering the escape of heal so trifling that it is nearly imperceptible. 



The interior diameter of the Jteam pipe is only 3 in. Upon stopping 

 the engine, the eccentric rod is not thrown out of gear, as is the usual 

 practice, but a cock in the steam pipe is shut, whereby the admissioa 

 of steam to the engine is totally prevented, and the quiescence of the 

 engine is the result. The cock by which this is accomplished is a 

 four-way cock, one of the channels through it being for the purpose of 

 maintaining the communication between the boiler and the slide valve, 

 and the other for accomplishing the operation of bloretng through. 

 The slide valves are of the common three-ported description, and are 

 situated at the upper extremities of the cylinders. The covers of 

 both cylinders are upon the same level, but the larger cylinder being 

 the longer projects downward further than the smaller one. This 

 peculiarity, however, is not observable to a spectator: the symmetry 

 of the work has been carefully and successfully preserved. The valve* 

 move simultaneously, and are put in motion by arms extending from 

 stout iron rods, which ascend through the floor of the engine-room, 

 and areguiiled in sockets attached to the respective cylinders to which 

 the valves belong. These rods derive their motion from i cross heaJ 

 which forms the upper side of a square frame, in which a heart-shaped 

 cam revolves, by which means the frame is moved alternately upwards 

 and downwards, the sides of the frame being so far apart that the cam 

 passes them in its revolution, without communicating any laler.J 

 motion. This arrangement has been long known under the name of 

 the hc'irt motion, but its extended eiuploymcnt has \\een prevented by 

 the impression that it produced a jarring and irregular motion, un- 

 favourable to the smooth working of machinery. This impression is, 

 in the present case, proved to be unfounded : the valves are movcil 

 without noise, tremor, or harshness of any kind. The advantage to 

 be derived from the use of the heart motion is a rapid opening and 

 closing of the port; but we believe the eccentric to accomplish this 



