NON-CONDENSING ENGINES.—LEUPOLD'S ENGINE.-TREVETHICK AND VIVIAN.—EFFECTS OF RAILWAY TRANSPORT.—HISTORY OF THE LOCOMOTIVE ENGINE.—BLENKINSOP.—MESSRS. CHAPMAN.—WALKING ENGINE.—MR. STEPHENSON'S ENGINES AT KILLINGWORTH.—LIVERPOOL AND MANCHESTER RAILWAY.—EXPERIMENTAL TRIAL.—THE ROCKET.—THE SANSPAREIL.—THE NOVELTY.—SUBSEQUENT IMPROVEMENTS IN THE LOCOMOTIVE ENGINE.—LARDNER'S EXPERIMENTS IN 1832.—ADOPTION OF BRASS TUBES.—MR. BOOTH'S REPORT.—DETAILED DESCRIPTION OF THE MOST IMPROVED LOCOMOTIVE ENGINES.—POWER OF LOCOMOTIVE ENGINES.—EVAPORATION OF BOILERS.—LARDNER'S EXPERIMENTS IN 1838.—RESISTANCE TO RAILWAY TRAINS.—RESTRICTIONS ON GRADIENTS.—COMPENSATING EFFECT OF GRADIENTS.—EXPERIMENT WITH THE HECLA.—METHODS OF SURMOUNTING STEEP INCLINATIONS.
(180.)
We are not, however, to understand that every engine, in which steam is used of a pressure exceeding that of the atmosphere, is what is meant by an high-pressure engine; for in the ordinary engines in common use, constructed on Watt's principle, the safety-valve is loaded with from 3 to 5 lbs. on the square inch; and in Woolf's engines, the steam is produced under a pressure of 40 lbs. on the square inch. These would therefore be more properly called condensing engines than low-pressure engines; a term quite inapplicable to those of Woolf. In fact, by high-pressure engines is meant engines in which no vacuum is produced, and, therefore, in which the piston works against a pressure equal to that of the atmosphere.
In these engines the whole of the condensing apparatus, viz. the cold-water cistern, condenser, air-pump, cold-water pump, &c., are dispensed with, and nothing is retained except the boiler, cylinder, piston, and valves. Consequently, such an engine is small, light, and cheap. It is portable also, and may be moved, if necessary, along with its load, and is therefore well adapted to locomotive purposes.
(181.)
Fig. 82.
A ([fig. 82.]) is the boiler, with the furnace beneath it; C C are two cylinders with solid pistons P P′, connected with the working-beams B B′, to which are attached the pump-rods R R′, of two forcing pumps F F′, which communicate with a great force-pipe S; G is a four-way cock ([66].) already described. In the position in which it stands in the figure, the steam issues from below the piston P into the atmosphere, and the piston is descending by its own weight; steam from the boiler is at the same time pressing up the piston P′, with a force equal to the difference between the pressure of the steam and that of the atmosphere. Thus the piston R of the forcing-pump is being drawn up, and the piston P′ is forcing the piston R′ down, and thereby driving water into the force-pipe [Pg324] S. On the arrival of the piston P at the bottom of the cylinder C, and P′ at the top of the cylinder C′, the position of the cock is changed as represented in [fig. 83.] The steam, which has just pressed up the piston P′, is allowed to escape into the atmosphere, while the steam, passing from the boiler below the piston P, presses it up, and thus P ascends by the steam pressure, and P′ descends by its own weight. By these means the piston R is forced down, driving before it the water in the pump-cylinder into the force-pipe S, and the piston R′ is drawn up to allow the other pump-cylinder to be re-filled; and so the process is continued.