Joseph Bunnett

1858. Concentric steam engine.

Joseph Bunnett (1797-1864). Prolific inventor, steam engineer, and founder of Bunnett and Co.

1839 'NEW PATENT CONCENTRIC STEAM-ENGINE.— Bunnett and Corpe, of Deptford, the patentees and inventors of the improved Iron safety-shutter, now in such high estimation and extensive use, have lately taken out letters patent for a concentric steam-engine. We shall first state the action of the engine, as we saw it at work in the patentees' manufactory, and then proceed to point out its advantages. In appearance it Is similar to a rotatory engine, but its action is of a decidedly different character. The circular case, forms in the lower half the steam-chamber, in which is accurately fitted a square piston, with Barton's patent metallic packing. Through the centre of the piston, and attached to it, is a concentric or ring-like piston rod, which at a point opposite to it (the piston) is firmly embraced and supported above by two connecting arms, having a double bearing upon a fixed shaft in the centre of the engine; on which they oscillate sufficient to allow the piston to reciprocate freely. The piston-rod is made of square steel, and works through two metallic stuffing boxes in the top of the steam-chamber; and from the side of one of the arms above mentioned projects a pin, to which is attached the connecting-rod transferring the power of the engine to the crank of the fly-wheel and gear. On each side of the steam-chamber are two distinct slide-valves, worthy of particular notice: they take their motion from an eccentric on the crank shaft, and have two slide boxes or covers, by which means no steam is lost by exhalation in the passages as in the single slide, the exhaust is also fully open at the commencement of the stroke, and remains so to any subsequent part of it that may be desired. By this arrangement of the valves, the steam can be worked expansively or not without cams, tappet, or gear of any kind, the slides of themselves cutting off the steam at any part of the stroke.
Having thus explained the structure of the engine, we will now proceed to show its mode of operation. The steam-valve being opened, and the exhaust valve closed on one side, and the contrary on the opposite side, the steam is admitted and propels the piston forward to the opposite side, when the steam- valves change their position and the steam is admitted on the opposite side, which again propels the piston back to its original position, and thus, by the backward and forward motion of the piston, it passes through two arcs of a circle, similar to a pendulum, and carries with it the annular piston, rod and the arms attached to it, thereby sets in motion the connecting-rod; the piston being entirely carried or suspended by the arms attached to the fixed centre shaft, is relieved of all tendency to wear irregularly, there being in fact, no pressure upon it beyond that of the springs necessary to keep the segments in their places. By the simple arrangement and working of the engine the connecting-rod has a direct action, without the intervention of guide rods or parallel motion of any kind, and during the time that the greatest force is required upon the crank, it never forms an angle of more than five to ten degrees: its reciprocating motion describing an arc of a circle, which so nearly assimilates to the rotatory action of the crank, the changes of motion are effected with surprising ease and rapidity; and whether it be from the direct application of the force upon the crank alone, or the absence of parallel motion, or the power communicated as it were, upon an inclined plane, direct to the connecting rod, or by a combination of all these, very great power is most certainly gained.
The patentees have made several experiments, some of which we witnessed, proving the advantages of the position of their connecting rod and crank motion over the methods now in use in locomotive and other engines. By these it appears that in some positions of this crank, nearly double the power is obtained, and taking the average of a whole revolution of the crank an advantage of more than one third is gained; the experimental engine was set in motion in our presence, and with a piston of 24 inches superfices and a pressure of 20lbs only on the square inch, it exhibited great power, driving several lathes, drilling machines, &c. while without any load the crank performed upwards of 260 revolutions in a minute. It is the intention of the patentees to carry out these experiments to a practical result in a locomotive engine they are about to build, and they are also now engaged in executing orders for fixed engines, which will afford an opportunity of fully testing their power. We strongly recommend the engine to the notice of engineers, and advise them to avail themselves of the opportunity of forming their own judgement of its merits by examining the engine at work at the premises of the patentees, who will be happy to explain its action.— Civil Engineer and Architect's Journal.'

1840 Advert: 'Thames Bank, near Vauxhall-bridge, Middlesex Side.—To Engineers, Ironfounders, and Others. MR. FULHAM will SELL by AUCTION, on THURSDAY, Feb. 13, at Twelve, on the Premises, known as the late Beet-root Work, Thames Bank, a nearly new SIX-HORSE HIGH PRESSURE STEAM-ENGINE. by Bunnett and Corpe ; an eight-horse cylindrical boiler, six D gas retorts, a 36 in fan blowing machine, a wrought iron cupola furnace seven feet high, a Fairburn's patent machine to weigh half a ton, the brick fixing, shafting, iron rigger wheels, and other items.— May be viewed until the sale.' Catalogues of Mr. Fulham, 41, Threadneedle-street.'

1858 'These improvements have reference to a peculiar form of steam engine, for which Mr. Joseph Bunnett (one of the present patentees), obtained her Majesty's royal letters patent, bearing date the 14th June, 1838, and to which he gave the name of a concentric steam engine. The present improvements, by Joseph and Joseph George Bunnett, of Deptford, Kent, consist in the employment of a solid annular piston rod working round a circular guide instead of on a central axis as heretofore ; also in placing the steam-ways in the central part of the engine, and working the same by a single slide, which renders the two slide valves with their connecting gear formerly employed unnecessary, and also enables the whole of the internal working parts to be got at by taking off one side covering plate without disturbing any other parts of the engine. ....'

1864 Death notice: 'On the 14th inst, at New Cross-road, J. Bunnett, Esq., in the sixty-seventh year of his age.'

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