STEAM-CARRIAGE. A name usual ly applied to locomotive engines adapted to work on common roads.
The principle of the construction of these is in the general conditions, similar to that of the locomotive engine used on railways (855 LOCOMOTIVE ENGINE) ; but the engine adapted to common roads must have the same power, with a much less weight • or in other words, the ratio of the weight of the engine to the eva porating power of the boiler is much less than in the case of railway locomotives.
The first carriage was that of Messrs. Trethevick and Vivian, in 1802, 20 years after Mr. Griffith's improvement. Mr. Gordon, followed with various others, down to that of Sir J. Anderson, which appeared only a few years back.
The engine in steam-carriages general ly acts either directly on the wheels, and causes them to revolve, and thereby pro pels the carriage ; or it acts on cranks formed on the axle of the wheels, and the wheels being keyed upon the axle are compelled to revolve with it. In either case, the revolution, whether of the wheels or the axle, is produced by a connecting rod jointed on the end of the piston rod, and receiving motion from the piston rod. The wheels are generally driven by two pistons working in two cylinders, so that one is at its dead point when the other is in the position most favorable for its action. The arrange ment of this part of the machinery being similar to that of the railway locomotive, need not be here more fully described. The steam-carriages of different pro jectors differ one from another, chiefly in the boilers, and in the apparatus for generating the steam and admitting it to the cylinder. Mr. Gurney's boiler con sisted of a series of strong iron tubes placed side by side, so as to Ibnn the bars of the grate of the furnace. These were connected with another system nearly at right angles to them, forming the back of the furnace, and these again with a third system, forming the roof of the furnace. The tubes forming the grate bars had their ends inserted in a strong iron cylinder, having its axis horizontal, and its length extended across the front of the rurnace under the fire door • and the tubes forming the roof of the furnace were inserted in a similar cylindrical vessel, extending in like man ner across the front of the extending above the fire-door. These two cylinders were
likewise connected by upright cylinders of less diameter placed at each side of the fire-door. These systems of tubes and cylinders being filled with water, the heat of the furnace acting on the tubes surrounding the fireplace, and the heated air and flame being afterwards conducted above the tubes forming the roof of the fireplace, before it escaped into the chimney, steam was produced in the tubes, which by its lightness pass ed from them to the cylindrical vessel ex tending over the fire-door. From that vessel the steam passed into a larger cy lindrical vessel above it, called a separa tor, its purpose being to disengage the pure steam from the spray of water with which it is generally mixed when it first escapes from the boiling water in a state of violent agitation.
Every part of this boittr being cylin drical, has the form whien is most favor able to strength, and which, within given dimensions, contains the greatest quan tity of water. The tubes surrounding the furnace can freely expand in the direc tion of their length, without being loos ened at the joints, and without straining any part of the apparatus. Proper means of opening the tubes at their ends are provided, by which they may be scraped on the inside, and cleansed from any de posit which may be left in them by the water evaporated in them.
The boiler must have the power of generating steam rapidly, strength to secure it from explosion, lightness and compactness. A strong draft on the fire is produced either by an air chamber, or air fans. The operation of steering is usually performed by a hand-wheel at the forepart, giving motion by means of a rack and pinion, or chain and pulley to the fore axle. The brake by which the motion of the steam-engine is arrested usually consists of metal bands capable of be ing pressed either against the nave or the periphery of the one or both the after wheels.