emery, so as to make them a perfectly tight fit (Fig. 37). They were opened when necessary by means of weighted levers, and when shut were kept close by the pressure of the steam.1 FIG. 36.-WATT'S DIAGRAM, SHOWING EXPANSION OF STEAM, 1782. The boilers employed by Savery and Newcomen were of a circular form, the hot air being carried round in the form of a spiral, on its way from the 1 Farey on the Steam Engine, p. 373-4. xv.] RIVAL ENGINES. 181 furnace to the chimney. Watt elongated his boilers into the form known as the waggon boiler, the hot air being carried round its sides as before. By this alteration a larger proportionate surface was exposed to the action of the heat, and a greater economy of fuel was obtained, together with increased evaporative power. Watt appears at no time to have followed Newcomen's plan of placing the cylinder immediately over FIG. 37.-FORM OF VALVES EMPLOYED BY WATT. the boiler, but always upon a separate foundation alongside of it. The great success attending the introduction of Watt's engines led to several attempts to construct engines of different forms, with a view to the evasion of his patent. Conspicuous among these were the compound, or double-cylinder engine, of Jonathan Hornblower, and the direct-acting, or inverted cylinder engine, of William Bull.' Both Hornblower and Bull were Cornish engineers. They were well acquainted with the construction of Watt's engine; the latter had been employed as a stoker, and afterwards as an engineman, by Boulton and Watt.2 The form of Hornblower's engine is shown in Fig. 38. It was designed to utilize the expansion of the steam from the smaller into the larger cylinder. Being a single-acting engine, when it was at rest the pistons remained at the top of their respective cylinders. The action of the engine was as follows: all the valves having been opened, steam was blown through to expel the air from the cylinders, pipes, and condenser, and fill them with steam. The equilibrium-valves of both cylinders having been closed, and the steam-valves and exhaust-valve being open, on the injection water 1 A curious and little-known form of two-cylinder engine was invented by Adam Heslop, and patented in 1790. The cylinders were at opposite ends of the beam, and were known as the hot and cold cylinders respectively. A number of Heslop's engines were erected at collieries in Cumberland, both for winding and pumping purposes, but they appear to have been unknown beyond the limits of this county. For descriptions of these engines see Transactions of the Cumberland and Westmorland Antiquarian and Archæological Society, Part II. Vol. III., for 1877-8, p. 292.-The Heslop Engine, &c., by H. G. Fletcher, read at the meeting of the Institution of Mechanical Engineers in London, 17th Jan., 1879.-Engineering for Jan. 31st, 1879. 2 Muirhead's Life of Watt, 2nd ed., p. 391. being thrown into the condenser a vacuum was produced under the piston of the large cylinder, which, in consequence, was pressed down by the steam flowing into the top of the large cylinder through the pipe communicating with the bottom of the small cylinder, the steam from the boiler meanwhile following the little piston downwards, and pressing upon it with increasing effect as the expansion of the steam reduced the pressure beneath it. On the pistons arriving at the bottom of their strokes, the steam and exhaust valves were closed, and the equilibrium-valves of both cylinders were opened, whereupon the weight of the pump-rods carried the pistons back to the top of the cylinders, the steam which had previously been above each piston flowing through the communicating pipe and filling the cylinders below the pistons. The engine was then ready for another stroke, which followed immediately upon the equilibrium-valves being closed, and the steam and exhaust valves being again opened. Hornblower obtained a patent for his engine, in July, 1781. He became associated with a Mr. Winwood, of Bristol.2 His first engine was erected at Radstock, near Bristol, in 1782.3 The cylinders were nineteen 1 No. 1298. He is described as "of Penryn, in the county of Cornwall, plumber and brazier." 2 Pole on the Cornish Engine, p. 38, note. An Address to the Mining Interest of Cornwall, by Thomas Wilson, 1793, p. 4. 3 Muirhead's Life of Watt, 2nd ed., p. 388. Mechanical Inventions of James Watt, Vol. II., pp. 152, 161. |