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1839.] THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL BUNNETT AND COUPE'S CONCENTRIC STEAM-ENGINE. Fig 1. Elevation of a High-pressure Engine 199 Fig. 2. A Longitudinal Section talced through tire centre of the Engine. The letters of reference are the same in both sections. A—Is the fixed shaft in the centre of the engine, on which the connecting arms supporting the piston rod, and carrying a cross head nr pin for the connecting rod to oscillate freely upon. B—Steam chamber in which the piston reciprocates. C—Piston. D— Circular piston rod, which is made of square steel, admitting of metallic packing to the stuffing boxes. E—Blockings against which the outside covers of the cylinder are bolted, and also carrying the metallic stuffing boxes. FF—Tbe slide valves shewn at one-third of the stroke. G—Tire Exhaust. HH—The pipes conveying the steam to the slide valves. II—The connecting arms oscillating on the fixed centre shaft, and carrying the weight of the piston, piston rod, &e. KK—Are the steam ports. BUNNETT AND CORPE’S NEW PATENT CONCENTRIC STEAM-ENGINE. Messrs. 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, drawings of which we have given above. We shall first state the action ol the engine, as we saw it at work in the paten i tees' manufactory, and then proceed to point out its advantages. It will he seen, that in appearance it is similar to a rotatory engine, but its action is of a decidedly different character. The circular case, as shown in figures 1 and 2, forms in the lower part 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 con necting arms, having a double hearing 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 ofone 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- chamberare 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 exhaustion in the passages, as in the single slide, the exhaust is also fully open at the No. 21 Vol. II.—JudE, 1839.' Fig. 3. Transverse Section taken through the centre of the Engine. 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 he 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 tile 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 at tached 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 from 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 connect ing 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 i five to ten degrees ; its reciprocating motion describing an are 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 from the power being com municated as it were, upon an inclined plane, direct to the connecting- rod, or by a combination of all these, very great power is most cer tainly 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, we have annexed a table of these experiments. By these it will be seen that in some positions of the crank, it having just passed its centre, 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 201bs. 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