Beam Engine. - Lever Engine.-Napier's Direct Action Engine. - Seaward's Gorgon Engine. - Penn's Direct Action Engine.-Steeple Engine. - Galloway's Inverted Cylinder Engine. - Humphrey's Trunk Engine. - Parkyn's Sliding-cover Engine. - Maudslay's Concentric Cylinder Engine. - Maudslay and Field's Double Cylinder Engine. - Hick's Inverted Double Cylinder Engine. - Maudslay and Field's Direct Action Screw Propeller Engine. - Brunei's Inclined Cylinder Engine. - Penn's Oscillating Engine. - Borric's Rotatory Engine. - Condensation of Steam. - Seaward's Salt-water Gauge. - Maudslay and Field's Pumps. - Brunei's Condenser. - Napier's Condenser in the "Kilmun." - Howard's Condenser. - Dr. Church's Condenser. - S. Hall's Condenser in the " Wilberforce." - S. Hall's Salt-water Still. - Parallel Motion. - Reversing Motion. - Seaward's Slide Valves. - Morgan's Balance Valves. - Piston-slide Valves. - Expansion Valves. - Snodgrass's Expansion Valves. - Bourne's Slide Expansion Valves. - Ordinary Steam-boat Boiler. - Separate Elliptical Boilers. - Boilers of the " Syrius." - " United Kingdom" Boilers. - D. Napier's Tubular Marine Boilers. - Safety Valves.
Marine engines, In general, differ in their construction from those used on land in several points. As the weight of the machinery of steam-vessels, and the space which it occupies, necessarily excludes a portion of the cargo, it becomes an object of the greatest importance to diminish that weight and space to the utmost degree compatible with the requisite stability and means of working. These essential qualifications should be sought for by the adoption of the most judicious forms for obtaining the greatest strength and solidity with the least quantity of material. Marine engines should also be as simple as possible, consistently with their efficient performance: as they are exposed to Beverer trials than any other class of engines, they are consequently more liable to derangement; and the delays and expense attending repairs become serious evils, as the profitable employment of the vessel is thereby suspended.
An important consideration is, the position of the centre of gravity, which should be placed as low as possible, in order to obtain the greatest degree of stability for the vessel; as a very slight heel or lateral inclination of the vessel materially increases the load upon the engines, and detracts from the speed.
From these and other considerations, the arrangements and proportions commonly observed in land engines require to be modified for marine purposes. The length of the stroke is much shorter in proportion to the diameter of the cylinder than is usual in land engines; the length of the stroke seldom exceeding the diameter of the cylinder by more than a sixth, and frequently being even less than the diameter. The beam likewise is shorter, being generally rather less than three times the length of the stroke; and instead of having only a single beam, the centre of which is placed considerably higher than the centre of the shaft, there are two beams working outside the side frames, and the centres are placed as low down as the vibration of the beam will admit, the connecting rod working upwards instead of downwards. This arrangement originated in Scotland, and, we believe, with Mr. David Napier, of Glasgow.
The shaft is considerably higher than the top of the cylinder, and the frame which carries it is braced to the cylinder by a strong diagonal truss. As an unlimited supply of injection-water can be obtained without the use of a pump, the cold-water pump is dispensed with, and also the cold-water cistern, which, in land engines, usually surrounds the condenser. The motion of the vessel precludes the ordinary mode of feeding the boiler by means of a feed-head and a regulating float; the water is therefore conveyed direct from the feedpump to the boiler, and the supply is regulated by hand, by means of regulating valves or cocks.
Owing to the rapidly corrosive action of sea-water upon iron, whether malleable or cast, it is found necessary to construct all the moving parts of the engine which are exposed to it of copper or gun-metal; the air-pumps are therefore lined, and the air pump rods sheathed, with copper or gun-metal, and all the valves and cocks, and the plungers of the feed and bilge pumps, are made of brass or gun-metal.
Marine engines are generally of the class known as Beam Engines, in which the action of the piston is transmitted to the crank by a beam, whose fulcrum is in the centre of its length; we shall therefore commence our description with one of this class.