376 DESCRIPTION OF PLATES.
CHAPTER X.description of plates.
Plates 1 and 2. —These plates are described by thefirm as follows:—
The engines are of 300 horse-power, nominal power,manufactured by Messrs. Maudslay, Sons, and Field,having three horizontal cylinders, 55 inches in diameter,with a stroke of 2 feet 6 inches, giving motion to a three-throw crank shaft, with the cranks set at an angle of120° with each other. The cylinders are entirely casedwith steam, having steam jackets around their circum-ferences and at their ends, and are intended to workwith a pressure of 25 lbs. per square inch. The steamis cut off by the slide valve at from ^ to £ of the stroke,without the use of any separate expansion valves. Theslides are double ported as far as the eduction passagesare concerned, but they have three steam openings inorder to give the requisite area to the admission of thesteam. The slides are worked by a crank shaft runningacross the whole length of the engines, and driven by atrain of spur wheels from the main crank shaft of theengines. The two intermediate wheels of this train aremounted in a movable frame, which may be raised orlowered at pleasure, the effect of which is to vary theposition of the cranks that work the slides, so as tomake them cut off sooner or later, as may be required:by the same means the slide cranks are shifted into theproper position for going astern. There are two surfacecondensers, fitted with inclined tubes, with the steaminside the tubes, and the condensing water outside, asoriginally adopted by Samuel Hall. The steam passesinto the condenser at the upper end of the tubes, andthe condensed water is delivered at the lower end, fromwhence it passes to the air-pumps. Each condenser isfitted with 2,436 copper tubes, 6 feet 3 inches long,r;-inch diameter inside, with a thickness of No. 18 wire-gauge. The tubes are packed at each end with smallscrewed stuffing boxes with tape packings. The con-densers, with their corresponding air-pumps, are placedopposite the two outer cylinders, the air-pumps beingworked by brackets secured to the piston rods. Thespace between the two condensers over the cylinder
cross-heads and piston rods is occupied by the engineplatform; by this arrangement all the working partsare kept well within the reach of the person in charge.Motion is imparted to the circulating pumps by rods,connected with the steam pistons; these pumps are10J inches diameter, and 2 feet 6 inches stroke, and arefitted with lignum-vit® packing to the plungers, andindia-rubber foot and discharge valves. The condensedwater is delivered from the air-pumps into a feed-watertank, from which it is forced into the boiler by theordinary feed pumps. This description of engine offersthe advantage of great economy of fuel, with a compara-tively simple arrangement, while at the same time itgives an equable power, and the centre of gravity ofthe different moving parts being always the same inrelation to the vessel, it does away with all the un-pleasant vibration so frequently felt with quick-workingengines.
The steam is generated in two boilers, of the ordinarytubular construction with return tubes over the furnaces,placed one on either side of the vessel, with the stoker’sroom between them. Each boiler has four furnaces,3 feet 2 inches wide, and 6 feet 7 inches long, and isfitted with 440 brass tubes, 2-J inches diameter outside,and 6 feet long; the chimney is 5 feet 6 inches diameter,and it is made to lower on the telescope principle.
Each of the boilers is fitted with a superheating appa-ratus, consisting of a series of flattened tubes, placed inrows in the up-take : the tubes are placed so as to offeras little obstruction as possible to the heated air in itspassage to the chimney; each superheater has 81 tubes,6 feet 6 inches long, and inches diameter before theyare flattened.
The screw-propeller is four-bladed, with an increasingpitch on Mr. Woodcroft’s principle; it is 12 feet dia-meter, and has a mean pitch of 13 feet. The blades arebolted on to a spherical boss, and they are made so thatthe pitch can be altered and set at any pitch, from 11 f ee *6 inches to -14 feet 6 inches.
The vessel is an iron-plated battery ship, with a ram
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