The Neath Abbey
ÒPerseveranceÓ, 1832
Source: Lewis,
M. J. T. , Steam on the Penydarren
The PERSEVERANCE was a geared 0-6-0, with cast iron wheels 3ft-1in in diameter of a pattern favoured by Neath Abbey. The frame, like that of its successors, was singularly slight, made of flat bar iron 3in by 1in with stayed cross members near the ends for the coupling bars. The boiler plates were ⅜in thick. There was a domed front to the boiler, acting perhaps as a crude smoke-box, on which was mounted a box which held the swivels of the two chimneys. These reached a height of about 16ft above the rails, were held up by diagonal stays, and were raised by winch, though the drawings give no details. The 10½in by 20in cylinders were inclined and set at the back of the boiler, a position inaugurated by Robert Stephenson in 1828, but at variance with Neath Abbey's early preference for vertical cylinders and a bell-crank drive, or horizontal cylinders and a rocking beam drive.
The crankshaft was mounted on bearing frames attached at either end to the horn blocks of the front two axles, so that it was sprung. It carried the driving pinion A, which could be slid sideways along a square section of the shaft by a sheave operated by crank and rod from the footplate. For adhesion drive, pinion A engaged gear B (which was loose on the crankshaft) by means of a clutch, and B drove the front two axles by gears C and D, while the rear axle was driven by coupling rods. For rack drive, B was left idling and A was slid back to mesh with gear E on a short axle which carried the rack wheel F. When not in use, the rack axle was raised to clear pointwork. Its bearings were mounted on a U‑frame, whose opposite end was raised or lowered by lever from the footplate. The U‑frame was carried centrally on two large hoops, one attached to a crankshaft bearing frame, the other to a similar cross frame between the main axles; the latter hoop was wide enough to allow the pinion A to slide through it. Like the earlier design, PERSEVERANCE could not run by adhesion and rack at the same time; by adhesion it travelled 9ft 8in per revolution of the crank, by rack 3ft 11in. The cast iron rack rail, with teeth at 6in pitch, was laid with its centre line 1ft 2in from the outer face of the running rail.
The details of the valve motion are not precisely given, but they seem to have followed contemporary Neath Abbey practice in those days before link motion or even gabs. Pinion G on the crankshaft drove gear H. The axle of gear H was mounted on a bracket attached to the crankshaft bearing frame (and was thus sprung) and had two small-throw cranks at the end, from which rods transmitted the motion to the "Y‑shafts" mounted on top of the boiler backplate. From here rocker arms actuated the slide valves. Gear H was loose on the valve crankshaft, which was hollow. Inside it was a sliding spindle with lugs projecting through slots in the shaft. These lugs, when the spindle was pushed in, engaged in keyways in the boss of H which in turn rotated the shaft. When the spindle was pulled out (via a crank, rod and probably a treadle on the footplate), the lugs coincided with a hollow ring in the boss and H turned freely without driving the shaft. To reverse, the driver put H out of drive, worked the valve cranks through 180 degrees by means of handles on the Y‑shaft, and put H back into drive. To stop, since the engine had no brakes, he put H out of drive, waited for half a revolution of the main crank, and put it back into drive.[2] In both cases the valve sequence was reversed. There was no variable cut‑off.
We do not know the precise arrangement of the controls for operating the drive clutch, rack lowering arm, or reversing gear. The whole design, though compact and ingenious, was made awkward by being sprung; in DOWLAIS, the next rack engine, though a similar set‑up was retained, the gearing was not sprung. PERSEVERANCE'S hollow-shaft reversing clutch was particularly curious, and it is no surprise that it was replaced by a more conventional clutch in 1840.
The safety valve was apparently a weight-loaded one (like that known to have been on DOWLAIS) mounted near the back of the boiler; it discharged into the exhaust pipe. The boiler feed pump was actuated by a small rod off the crosshead. It pushed water drawn from the tender through water heaters surrounding the exhaust pipes. The two exhaust pipes passed into the chimney support box and were bent up in short swiveling blast pipes, each in its own chimney; these pipes were parallel, not nozzled. Since the feed water heaters would cause some condensation of exhaust steam, each exhaust pipe had a downward-pointing pipe at the boiler front through which the condensate could run off. These pipes being much longer than the blast pipes and being finely nozzled, there would be little loss of blast. The engine had a "casing"; this possibly meant ordinary boiler lagging, but more likely a complete overall wooden box, approximately rectangular, such as adorned the ROYAL WILLIAM on the Gloucester & Cheltenham Tramroad, to prevent horses being frightened by the machinery. Of the tender, nothing is known except that it was four wheeled, and on each axle one wheel was fixed and one loose. No doubt it looked much like those on later Dowlais engines.
PERSEVERANCE seems to have been delivered early in June 1832. The following article, originally published in 1833 was found in Notes and Queries, A Medium of Inter-Communication for Literary Men, General Readers, Etc., 4th Series. Vol. 3, January-June 1869, London, 1869
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November 2009